CA2033679A1 - Method and system for optimizing audio imaging in an automotive listening environment - Google Patents
Method and system for optimizing audio imaging in an automotive listening environmentInfo
- Publication number
- CA2033679A1 CA2033679A1 CA002033679A CA2033679A CA2033679A1 CA 2033679 A1 CA2033679 A1 CA 2033679A1 CA 002033679 A CA002033679 A CA 002033679A CA 2033679 A CA2033679 A CA 2033679A CA 2033679 A1 CA2033679 A1 CA 2033679A1
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- 238000000034 method Methods 0.000 title claims abstract description 10
- 238000003384 imaging method Methods 0.000 title abstract description 6
- 230000005236 sound signal Effects 0.000 claims abstract description 46
- 230000035945 sensitivity Effects 0.000 claims description 9
- 239000003990 capacitor Substances 0.000 description 33
- 238000010586 diagram Methods 0.000 description 12
- 239000002131 composite material Substances 0.000 description 7
- 230000004044 response Effects 0.000 description 7
- 230000000087 stabilizing effect Effects 0.000 description 7
- 230000008878 coupling Effects 0.000 description 6
- 238000010168 coupling process Methods 0.000 description 6
- 238000005859 coupling reaction Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 4
- 238000007599 discharging Methods 0.000 description 3
- 238000009434 installation Methods 0.000 description 3
- 238000000926 separation method Methods 0.000 description 3
- 230000003466 anti-cipated effect Effects 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 241000370685 Arge Species 0.000 description 1
- 230000003321 amplification Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S5/00—Pseudo-stereo systems, e.g. in which additional channel signals are derived from monophonic signals by means of phase shifting, time delay or reverberation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
- H04R2499/10—General applications
- H04R2499/13—Acoustic transducers and sound field adaptation in vehicles
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S2400/00—Details of stereophonic systems covered by H04S but not provided for in its groups
- H04S2400/05—Generation or adaptation of centre channel in multi-channel audio systems
Abstract
METHOD AND SYSTEM FOR OPTIMIZING AUDIO
IMAGING IN AN AUTOMOTIVE LISTENING ENVIRONMENT
An improved audio system comprising input means for inputting first and second audio signals; first summing means for generating a sum signal comprising the sum of said first and second audio signals and for generating a first output signal;
inverting means coupled to said first summing means for generat-ing a phase inverted sum signal; second summing means coupled to said first audio signal and said phase inverted sum signal for generating a second output signal corresponding to the difference between said first audio signal and said sum signal; and third summing means coupled to said second audio and said phase inverted sum signal for generating a third output signal corresponding to the difference between said second audio signal and said sum signal.
IMAGING IN AN AUTOMOTIVE LISTENING ENVIRONMENT
An improved audio system comprising input means for inputting first and second audio signals; first summing means for generating a sum signal comprising the sum of said first and second audio signals and for generating a first output signal;
inverting means coupled to said first summing means for generat-ing a phase inverted sum signal; second summing means coupled to said first audio signal and said phase inverted sum signal for generating a second output signal corresponding to the difference between said first audio signal and said sum signal; and third summing means coupled to said second audio and said phase inverted sum signal for generating a third output signal corresponding to the difference between said second audio signal and said sum signal.
Description
ME~HOD AN~ SYSTEM FOR OPTIMIZING AUDIO
IMAGING IN AN AUTOMOTIVE LISTENING ENVIRONMENT
Field of the Invention S T~is invention relates to the ~ield of audio signal processing and more specifically to a method and system for optimizing the audio image perceived by a driver and passengers in an automotive listening environment.
~ackaround of the Invention . . , Audio systems have become increasingly popular in recent years, and much development effort has been directed toward improving the guality and integrity of their audio imaging. One important aspect of audio imaging is the creation of a sound field in which a listener perceives depth and directional qualities in the sound field created by a plurality of sources.
One example o~ a multi-channel audio system which provides an enhanced sound field is described in United States Patent Nos. 3,632,886, 3,746,792, and 3,959,590, all invented by Scheiber~ In Scheiber's system, as many as ~our audio channels may be encoded to two channels for recording or transmission and decoded at playback to produce multiple channels ~typically four) of audio information. In this type of system, speakers or transducers are placed peripherally around a listener to produce a sound fiQld in which sound may be perceived as originating from substantially any direction.
Another example of a multi-channel audio system which provides an enhanced sound field is the well known ~surround sound~ audio system designed by Dolby La~oratories. In this system, multiple channels of audio information are also encoded to two channels for recording and decoded at playback to produce a multi-dimensional sound f ield. In this system, the primary sound sources are located in front of a listener and secondary sound .
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sources are disposed peripherally around a listener to create the desired directional effects. This system is particularly popular for use with the audio portions of motion pictures.
Still another multi-channel sound system i5 described in United States Patent No. 4,478,167, invented by Borkin. Borkin teaches a three channel sound system in which speakers are located in a triangular pattern around a listener. In Borkin's system, a center channel signal is derived by summing a portion of left side channel signal and a portion of the right side channel signal. In addition, a portion of the right side signal is cancelled from the left side channel and a portion of the left side signal is cancelled from the right side channel.
lS According to Borkin, the proportions of the amount of side channel cancellation range from approximately 2/3-3/4 to achieve the desired results. In Borkin's system, the gain of each of the audio channels is identical and fixed, thus requiring transducers of equal size wherein the placement of the transducers relative to the listener is critical.
While each of the above systems provides an enhanced sound field in a spacious environment such as a home living room or movie theater, they are not particularly useful for use in an automotive environment.
As exemplified by the systems noted above, much development effort has been directed toward bolstering the directional information present in a sound field and the above systems function quite well in installations where sound sources and listeners can be positioned in optimal locations. However, in an automotive environment, the ~, .
location of listeners relative to sound sources cannot be readily adjusted. For example, sound sources in automobiles are typically placed in doors, side panels or rear decks, and once installed, cannot be moved. The position of the listeners, in this case a driver and one or more passengers, is necessarily fixed by the location of seats within the automobile. If the sound system is .
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adjusted to produce a balanced sound field proximateeither the driver or passengers, the sound field will be unbalanced near the other occupants of the automobile. No system is known which allows a sound field to be optimized for one occupant of an automobile while also providing an optimally balanced sound field for the other occupants of an automobile. Furthermore, no system is known which generates a balanced sound field in a center channel sound system wherein the components used in the center channel may be smaller than the side channel components and further wherein the placement of the center channel transducer is not critical.
SummarY and Ob;ects of the Invention Briefly described, the present invention contemplates an audio system for optimizing a sound field for a plurality of listeners positioned in diverse locations in a listening environment. In operation, first and second audio signals, typically comprising left and right audio signals, are input from an audio source. The first and second audio channels are summed to generate a composite audio signal. A portion of the composite audio signal is cancelled from the left and right audio signals to generate left and right output signals, respectively, wherein the composite audio signal comprises a center channel output signal. In one aspect of the present invention, the gain of the side channel cancellation signal is limited to .S to preserve substantially all of the perceptible directional information in the left and right side channels. In yet another aspect of the present invention, the center channel output signal is high-pass filtered to remove low frequency information from the center channel thus allowing a relatively smaller transducer to be used in the center channel. In yet another aspect of the present invention, the overall gain of the center channel is adjustable to allow the sensitivity of the center channel to be adjusted to match : . , : :: , . . :
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the center channel components to the other components used in the system.
In an alternate embodiment of the present invention, means are provided for deriving left and right S channel ambience signals wherein the ambience signals comprise the respective difference signals for each channel. Means are provided for injecting variable amounts of the left and right ambience signals into the left and right output signals, respectively, to provide a center channel stereophonic system having complete control over the level of difference signal information present in the respective side channels.
Accordingly, it is an object of the present invention to provide a method and system for providing an optimally balanced sound field for a plurality of listeners in diverse listening locations.
It is another ob;ect of the present invention to provide a method and system for evenly re-distributing the monophonic portion of a stereophonic sound field while leaving a substantial portion of the directional information intact.
It is yet another object of the present invention to provide a center channel in stereophonic sound system wherein the placement of the center channel 2S transducer is not critical.
It is still another object of the present invention to provide a multi-channel sound system for optimizing the sound field for a plurality of listeners in an automotive listening environment.
It is yet another object of the present invention to provide a method and system for evenly re-distributing the monophonic portion of a stereophonic sound field while also providing means for controlling the level of directional information present in the respective side channel signals.
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IMAGING IN AN AUTOMOTIVE LISTENING ENVIRONMENT
Field of the Invention S T~is invention relates to the ~ield of audio signal processing and more specifically to a method and system for optimizing the audio image perceived by a driver and passengers in an automotive listening environment.
~ackaround of the Invention . . , Audio systems have become increasingly popular in recent years, and much development effort has been directed toward improving the guality and integrity of their audio imaging. One important aspect of audio imaging is the creation of a sound field in which a listener perceives depth and directional qualities in the sound field created by a plurality of sources.
One example o~ a multi-channel audio system which provides an enhanced sound field is described in United States Patent Nos. 3,632,886, 3,746,792, and 3,959,590, all invented by Scheiber~ In Scheiber's system, as many as ~our audio channels may be encoded to two channels for recording or transmission and decoded at playback to produce multiple channels ~typically four) of audio information. In this type of system, speakers or transducers are placed peripherally around a listener to produce a sound fiQld in which sound may be perceived as originating from substantially any direction.
Another example of a multi-channel audio system which provides an enhanced sound field is the well known ~surround sound~ audio system designed by Dolby La~oratories. In this system, multiple channels of audio information are also encoded to two channels for recording and decoded at playback to produce a multi-dimensional sound f ield. In this system, the primary sound sources are located in front of a listener and secondary sound .
. ...~., ~, .. ~ ....
sources are disposed peripherally around a listener to create the desired directional effects. This system is particularly popular for use with the audio portions of motion pictures.
Still another multi-channel sound system i5 described in United States Patent No. 4,478,167, invented by Borkin. Borkin teaches a three channel sound system in which speakers are located in a triangular pattern around a listener. In Borkin's system, a center channel signal is derived by summing a portion of left side channel signal and a portion of the right side channel signal. In addition, a portion of the right side signal is cancelled from the left side channel and a portion of the left side signal is cancelled from the right side channel.
lS According to Borkin, the proportions of the amount of side channel cancellation range from approximately 2/3-3/4 to achieve the desired results. In Borkin's system, the gain of each of the audio channels is identical and fixed, thus requiring transducers of equal size wherein the placement of the transducers relative to the listener is critical.
While each of the above systems provides an enhanced sound field in a spacious environment such as a home living room or movie theater, they are not particularly useful for use in an automotive environment.
As exemplified by the systems noted above, much development effort has been directed toward bolstering the directional information present in a sound field and the above systems function quite well in installations where sound sources and listeners can be positioned in optimal locations. However, in an automotive environment, the ~, .
location of listeners relative to sound sources cannot be readily adjusted. For example, sound sources in automobiles are typically placed in doors, side panels or rear decks, and once installed, cannot be moved. The position of the listeners, in this case a driver and one or more passengers, is necessarily fixed by the location of seats within the automobile. If the sound system is .
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:-: :~
:, .
adjusted to produce a balanced sound field proximateeither the driver or passengers, the sound field will be unbalanced near the other occupants of the automobile. No system is known which allows a sound field to be optimized for one occupant of an automobile while also providing an optimally balanced sound field for the other occupants of an automobile. Furthermore, no system is known which generates a balanced sound field in a center channel sound system wherein the components used in the center channel may be smaller than the side channel components and further wherein the placement of the center channel transducer is not critical.
SummarY and Ob;ects of the Invention Briefly described, the present invention contemplates an audio system for optimizing a sound field for a plurality of listeners positioned in diverse locations in a listening environment. In operation, first and second audio signals, typically comprising left and right audio signals, are input from an audio source. The first and second audio channels are summed to generate a composite audio signal. A portion of the composite audio signal is cancelled from the left and right audio signals to generate left and right output signals, respectively, wherein the composite audio signal comprises a center channel output signal. In one aspect of the present invention, the gain of the side channel cancellation signal is limited to .S to preserve substantially all of the perceptible directional information in the left and right side channels. In yet another aspect of the present invention, the center channel output signal is high-pass filtered to remove low frequency information from the center channel thus allowing a relatively smaller transducer to be used in the center channel. In yet another aspect of the present invention, the overall gain of the center channel is adjustable to allow the sensitivity of the center channel to be adjusted to match : . , : :: , . . :
-, . :
the center channel components to the other components used in the system.
In an alternate embodiment of the present invention, means are provided for deriving left and right S channel ambience signals wherein the ambience signals comprise the respective difference signals for each channel. Means are provided for injecting variable amounts of the left and right ambience signals into the left and right output signals, respectively, to provide a center channel stereophonic system having complete control over the level of difference signal information present in the respective side channels.
Accordingly, it is an object of the present invention to provide a method and system for providing an optimally balanced sound field for a plurality of listeners in diverse listening locations.
It is another ob;ect of the present invention to provide a method and system for evenly re-distributing the monophonic portion of a stereophonic sound field while leaving a substantial portion of the directional information intact.
It is yet another object of the present invention to provide a center channel in stereophonic sound system wherein the placement of the center channel 2S transducer is not critical.
It is still another object of the present invention to provide a multi-channel sound system for optimizing the sound field for a plurality of listeners in an automotive listening environment.
It is yet another object of the present invention to provide a method and system for evenly re-distributing the monophonic portion of a stereophonic sound field while also providing means for controlling the level of directional information present in the respective side channel signals.
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2~3367~
Br ef Description of the Drawinas These and objects will be readily apparent to persons of ordinary skill through the detailed description of the invention below and the accompanying drawings in which:
Figure lA is a block diagram of the improved audio system of the present invention.
Figure lB is a block diagram of an alternate embodiment of the present invention.
Figure 2 is a diagram of one possible transducer arrangement in an automotive listening environment in accordance with the principles of the present invention.
Figure 3A is a schematic diagram of a portion of the system of Figure lA.
Figure 3B is a schematic diagram of another portion of the system of Figure lA.
Figure 3C is a schematic diagram of ~ circuit for remotely controlling the system of Figure lA.
20Figure 4A is a schematic diagram of a portion of the system of Figure lB.
Figure 4B is a schematic diagram of another portion of the system of Figure lB.
Figure 4C is a schematic diagram of yet another portion of the system of Figure lB.
Figure 4D is a schematic diagram of a circuit for remotely controlling the system of Figure lB.
Detailed Descri~tion of the Invention 30Figure 1 is a block diagram of the preferred embodiment of the present invention. In the system 100, first and second channels of audio information, typically referred to as left and right side channels, are coupled to a summing means 102 which generates a co~bined left plus right (L+R) audio signal. In the preferred practice of the present invention the summing means 102 limits the gain of the combined L+R audio signal to .5. The output , . ' `~' ;
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of summing means 102 is coupled to high pass filter 104 which blocks low frequency information in the combined L+R
audio signal. The high pass filter 104 is preferably a conventional highly damped Bessel slope filter having a S slope of approximately -18dB/oct. The output of high pass ; filter 104 is coupled to level control 106 which adjusts the gain of the combined L+R audio signal to limit the level of monophonic information in the center channel to a desired amount. The output of level control 106 is coupled to a level matching network 108 which allows the overall gain of the combined L+R audio signal to be ad~usted to match the sensitivity of the output components used in the left and right side channels.
The output of level control 106 is further coupled to phase inverter 110 which shifts the phase of the combined L+R audio signal by 180 degrees. The output of phase inverter 110 is further coupled to summing means 112, 114 which sums the inverted, gain limited, high pass filtered L+R audio signal with the respective left and right side channel signals to remove a portion of the monophonic center channel information from the left and right side channels, thus providing and maintaining a constant level of monophonic information in the overall sound field. While the system 100 is shown as 2S incorporating an inverter 110, those skilled in the art will appreciate that the inverter 110 may be incorporated in summing means 112, 114 by providing summing means with inverting and non-inverting inputs.
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The relationship of the respective center and side channels of the system 100 is defined by the following equations:
' L s L - K(L+R) R - R - K(L+R) C = 2K(L+R) .
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2~33679 where:
L = left side signal R = right side signal K = monophonic cancellation gain (limited to K=.5) 2K = center channel output gain In practice, the variable gain center channel provides the following output relationships:
CENTER K LEFT RIGHT CENTER SEPARATION
SETTING CHANNEL CHANNEL CHANNEL LIMIT
0% O L R O MAX
50~ .25.875L .875R .25(L+R) 17dB
-.125R -.125L
100% .5.72L .75R .5 (L+R) s.5dB
-.25R -.25L
200% 1.5L-.5R .5R-.5L L+R OdB
(limit) Referring now to Figure lB, in another embodiment of the present invention, the system 150 includes means for controlling the "ambience" of a sound field. For the sake of clarity in the description below, ; 30 items which perform identical functions bear identical designations. An ambience signal may be thought of as a side channel difference signal wherein the frequency response of the difference signal may be modified. After processing, the ambience signal is injected into the left and right side channels in a variable amount to achieve a desired effect. In practice, the ambience signal for the left side channel comprises a (L-R) difference signal and ambience signal for the right side channel comprises a (R-L) difference signal. In the system 150, a left minus right (R-L) signal is derived by difference signal generator 152. In the preferred practice of the present 203367~
invention, the gain of the difference signal generator 152 is limited to .5 to prevent clipping distortion of maximum amplitude input signals at the difference amplifier output. The output of difference signal generator 152 is coupled to tone control 154 which alters the frequency response of the difference signal. The output of tone control 154 is coupled to level control 156 which controls the amount of ambience signal added to the respective left and right side channel signals. The output of level control 156 is coupled to an inverter circuit 158 which generates the right minus left (R-L) ambience signal. The system 150 incorporates three input summing circuits 112', 114' which are essentially identical to summing circuits 112, 114 with the addition of an additional input. In the system 150, the center channel signal is derived in an identical manner as the system 100. The processed left and right side channel signals are generated in a similar manner as the system 100 wherein summing circuit 112' sums the output of inverter 110 (which comprises the inverted or phase shifted center channel signal), the left side channel signal, and the L-R ambience signal.
Similarly, the summing circuit 114 sums the output signals of inverter 110, inverter 158 (which comprises the R-L
ambience signal) and the right side channel signal. The following equations define the relationships between the ~nput and output signals in the system 150.
; C = K(.5L+.SRI
L = (.SJL - .5JR) - K(.5L~.5R) = L - K(.5L + .5R) R s (.5JR - .5JL) - K(.5L+.5R) = R - K(.5R - .5L) ~' where:
C = center signal L = left side signal R = right side signal X = monophonic cancellation gain (limited to K =
.5(K= 0 - 5)) ,. ~ ,' ... ,. ~ -. - ~
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i J = ambience injection gain (J= (0-3)) A typical installation for the improved audio system of the present invention is shown in Figure 2. In S the installation 200, the system 100 typically receives audio left and right input signals from an audio source (not shown) such as the output of a cassette deck, compact disk player, tuner, etc. Depending on the specific application, other components such as an equalizer or a 10 preamplifier may be inserted in series between the audio source and the system 100. The system 100 processes the left and right input signals to generate left side channel, right side channel and center channel signals which are amplified by power amplifiers 162-166, 15 respectively. Transducers 168, 170, coupled to the respective outputs of power amplifiers 162, 170 are typically of the same size and sensitivity and would typically be mounted in the doors, side panels, or rear deck of automobile 172. However, in an automobile, 20 options for locating a center channel transducer are quite limited. Therefore, the present invention contemplates the use oS a frequency limited center channel to allow a reduced size transducer 174 which may be mounted in a variety of locations such as an automobile dashboard where 25 space is limited. The present invention further provides a variable gain center channel so that the sensitivity of transducer 174 can be compensated to match the sensitivity of transducers 168, 170.
As can be seen in Figure 2, without the center 30 channel transducer 174, each of the passengers in automobile 172 is located in a position proximate a single side channel transducer. Thus, stereophonic imaging is minimized since each listener primarily hears the side channel closest to the listener. With the addition of the 35 side channel transducer 174, a portion of the signal from each of the side channels is relocated to the center of .
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the automobile 172 thus improving the image perceived by both passengers.
Referring now to Fiqure 3A, the system 100 receives left and right audio signals at terminals 202, 204, respectively. Input filters 206, 208, coupled to terminals 202, 206, respectively, provide noise filtering and input isolation. Input filter 206 comprises operational amplifier 218 which is disposed with an inverting input coupled to input terminal 202 through a broad bandpass filter formed by resistors 203, 207, and 214, and capacitors 205 and 210. Gain control feedback resistor 209 and filter capacitor 211 are connected in parallel between the output and the inverting input of operational amplifier 218. Input filter 208 is identical to input filter 206 and it includes resistors 213, 216, 217, 221, capacitors 212, 215, 223 and amplifier 220. The respective components of input filters 206, 208 are selected to provide a bandpass filter response of approximately lHz-200KHz.
The outputs of input filters 206, 208 comprise inverted left and right (-L,-R) input signals which are coupled to inverting summing network 102. Summing network 102 generates a composite (L~R) sum signal of the inverted left and right input signals. Summing network 102 includes resistors 222, 224, resistor 226, capacitor 230 and operational amplifier 228 wherein summing network 102 is configured to provide a gain of approximately .5.
Summing network 102 provides a relatively low impedance to the input sources to minimize distortion and to scale the input voltage to preserve the dynamic range in the system.
The output of summing network 102 is coupled to a voltage follower 103 which comprises operational amplifier 232 and resistors 234, 235. Voltage follower 103 reduces the gain of the composite L+R signal to compensate for the gain in following stages. The output of voltage follower 103 is coupled to the input of high pass filter 104 through coupling and filter capacitor 242.
2033~7~
High pass filter 104 blocks any low frequency information in the composite L+R signal.
The high pass filter 104 is preferably configured as a 3rd order steep slope bessel type filter having a slope of approximately 18 dB/oct. High pass filter 104 comprises operational amplifier 240, resistor 244, and capacitors 242, 246; and operational amplifier 250, resistors 252, 254, 256, capacitor 258 and stabilizing capacitor 260. In the preferred practice of the present invention, resistors 244, 248, 256 may be of the switc~able dip resistor network type to adapt the frequency response of the system loo for use with virtually any type of transducer and amplifier system. In the preferred practice of the present invention, the components are preferably selected to provide a cutoff frequency which may range from 20-350 Hz depending on the values of resistors 244, 248 and 256 with the frequency being chosen based on the low frequency characteristics of the center channel transducer.
Referring now to Figure 3B, the output of high pass filter 104 is coupled to the input of level control 106 through voltage-to-current converting resistor 262 and AC coupling capacitor 264 which is selected to pass any AC
signal above lOHz without any significant attenuation.
Level control 106 preferably comprises a 2150A voltage controlled amplifier (VCA) 266, manufactured by That Corporation, 15 Strathmore Rd., Natick, MA 01760. VCA
266 receives the current signal generated by resistor 262 and amplifies the current signal under the control of the voltage produced across resistors 268, 2io which form a 1:50 voltage divider. The voltage produced across resistors 268, 270 is controlled by NPN transistor 272 which is disposed with its emitter coupled to one terminal of resistor 270 and its collector coupled to the V+
positive voltage source. The base of transistor 272 is coupled to control terminal 274 through resistor 276 wherein the voltage on control terminal 274 controls the 203~7~
voltage generated across resistors 268, 270, and thus the gain of VCA 266. The control signal on terminal 274 is filtered by capacitors 278, 280 and resistor 282. VCA 266 preferably provides a gain sensitivity of 6mv/dB.
Therefore, the signal present on control terminal preferably varies from 0-6 volts, thus providing a variable voltage of approximately 0-60mv across resistor 268. This voltage scaling provides a relatively low impedance at control terminal 274 and minimizes the effect of any noise present at control terminal 274. It should be noted that as the voltage across resistor 268 increases, the gain of VCA 266 decreases The present invention contemplates the use of a +/-15 volt power supply to provide ample dynamic range capabilities in the system 100. The -15v voltage source is coupled to VCA 266 through resistor 285 and is adjusted to set the quiescent operating current of VCA 266. In addition, the adjustable voltage divider formed by resistors 284, 286, and variable resistor 288 is adjusted to compensate for symmetry irregularities in the output signal of VCA 266.
The control voltage coupled to control terminal 274 may be generated by virtually any type of voltage source. In the preferred practice it is anticipated that system lOO may be located remotely from a listener. For example, in an automobile, sound systems are frequently located in the trunk of the automobile. Since the present invention anticipates the use of a variable gain center channel, it is anticipated that the control terminal 274 may be coupled to a remote voltage source 275 which may be installed in the passenger compartment of an automobile. One remote voltage source adapted for use with the present invention is shown in Figure 3C. The remote voltage source 275 comprises a switch 386 having terminals 390, 392 and 394, diodes 388, 400, light emitting diode 402, resistors 404, 406, poteniometer 408 and filter capacitor 410. Resistor 406 and poteniometer 408 are coupled in series between the V+ power supply and :
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2~3367~
form a variable voltage divider 412 with the output of voltage divider 412 coupled to control terminal 274 through protection diode 400.
Terminal 390 of switch 386 is also coupled to the V+ power supply. When terminals 390 and 392 of switch 386 are coupled together, the V+ power supply is coupled to terminal 274 through protection diode 388. This forces transistor 272 to conduct fully, thus forcing VCA 266 into a minimum gain state, effectively disabling the system 100. When terminals 392 and 394 of switch 386 are coupled together, the V+ power supply is coupled to ground through light emitting diode 402 and resistor 206. This illuminates light emitting diode 402 and allows the voltage on terminal 274 to depend on the position of the wiper of potentiometer 408, thereby providing adjustable gain in VCA 266.
Referring again to Figure 3B, the oùtput of VCA
266 is coupled to current-to-voltage converter 290 which comprises operational amplifier 292, feedback resistor 294 and stabilizing capacitor 296. Current-to-voltage converter 290 converts the current signal output by VCA
266 into a voltage signal processed by the remainder of the system 100. The output of current-to-voltage converter 290 is coupled to the non-inverting input of center level match circuit 108, and the inverting inputs o~ summing amplifiers 112, 114 through resistors 332, 352, respectively.
Center level match 108 provides a nominal gain of 2 and may be adjusted +/- 15 db to match the system lO0 ~D ~V Y~ ~p~ n~ ~p~x~ ~y~e~s ~ic~ ~y ~e ~se~
with t~e system ~D0, F~r examp~e~ in many syste~s, ~arge speakers and amplifiers may be utilized for t~e left and right side channels. However, since the center c~annel is high pass filtered, a smaller transducer may be used in the center cbannel. ~he nominal gain of the center channel match 108 is set at 2 so that the overall gain of the center channel composite signal is unity with the side ~.
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channel signal cancellation limited to a gain of .5. The center channel match 108 may be adjusted to compensate for difference in the sensitivity in the components used in the center and side channels thus providing a balanced sound field in the listening environment. The center channel match 108 includes operational amplifier 300 wherein the non-inverting input of operational amplifier 300 is coupled to the output current-to-voltage converter 290 through resistor 298. Gain setting resistors 312, 314, 316 are selected to set the nominal gain of operational amplifier 300 at 2. Capacitor 310 provides high frequency filtering of the output of operational amplifier 300 to stabilize the amplifier 300. A
potentiometer 304 is coupled between the respective input 15 terminals of operational amplifier 300 and its wiper i5 commected to ground through resistor 306 and AC coupling capacitor 308. Potentiometer 304 causes either the input signal or the feedback signal to be partially shunted to ground thereby providing a plus or minus 15dB gain 20 ad~ustment of the signal at the output of the amplifier 300. The potentiometer 304 has a center detent to set the gain to 2 (i.e. 6dB). The output of operational amplifier 300 is coupled to the center channel output terminal 318 through resistor 320 and AC coupling capacitor 322.
25 Capacitor 324 filters noise on center channel output terminal 318. Load resistor 326 provides a discharging path for capacitor 322.
The summing amplifiers 112, 114 are configured as inverting amplifiers which sum the combined L+R center 30 channel signal with the respective inverted left and right side channel signals to eliminate any additional monaural information from being added to the overall sound field.
As noted above, the amount of L+~ center channel signal ;cancelled from the side channels is user selectable and is 35 controlled by level control 106. In the preferred practice of the present invention, the maximum side channel cancellation is limited to .5, thus providing a r `' ' ` ~ : '~ ' 203367~
minimum center channel separation of 9.5 DB. center channel separation improves at lesser levels of cancellation.
The inverted output signal of summing amplifiers 112, 114 comprise the left and right side channel signals defined by the equations set forth above. The summin~
amplifier 112 comprises operational amplifier 330 wherein the inverting input of operational amplifier 330 is coupled to the output of current-to-voltage converter 290 through resistor 332 and to the output of input filter 102 through resistor 333. The non-inverting input of operational amplifier 330 is coupled to system grounds.
Gain setting resistor 334 and stabilizing filter capacitor 336 are connected in parallel between the inverting input and output of operational amplifier 330. The output of operational amplifier 330 is coupled to the left side channel output terminal 338 through series resistor 340 and AC coupling capacitor 342. Capacitor 344 filters out noise on channel output terminal 338. Load resistor 346 provides a discharging path for capacitor 344. Similarly, The summing amplifier 112 comprises operational amplifier 350 wherein the inverting input of operational amplifier 350 is coupled to the output of current-to-voltage converter 290 through resistor 352 and to the output of input filter 208 through resistor 353. The non-inverting input of summing amplifier 114 is coupled to system ground. Gain setting resistor 354 and stabilizing filter capacitor 356 are connected in parallel between the inverting input and output of operational amplifier 350.
~he output of operational amplifier 350 is coupled to the right side channel output terminal 358 through series resistor 360 and AC coupling capacitor 362. Capacitor 364 filters noise on right channel output terminal 358. Load resistor 366 provides a discharging path for capacitor 364.
Referring now to Figure 4A, a portion of the ~ system 150 is shown in schematic form. For the sake of :
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clarity, components which perform identical functions in the system 100 bear identical designations and are not further discussed below. In addition to the circuitry of system 100, the system 150 includes difference signal S generator 152 for deriving the difference between the left and right input signals. Difference signal ~enerator 152 includes operational amplifier 502 which is disposed with its inverting input coupled to the output of input filter 206 (which comprises the -L input signal) through resistors 504, 506, and its non-inverting input coupled to the output of input filter 20~ (which comprises the -R
input signal) through resistors 508, 510. Filter capacitor 514 and load resistor 512 are coupled in parallel between the non-inverting input of operational amplifier 502 and system ground. Feed~ack resistor 516 and stabilizing filter capacitor 518 are coupled in parallel between the inverting input and output of operational amplifier 502. While the difference signal generator 152 is coupled to -R and -L input signals, in practice, by virtue of the input phasing, the output of difference signal circuit 152 comprises a L-R difference signal. While various signal inversions may oacur during the detailed operation of the circuitry of Figures 4A-4D, the circuit remains functionally equivalent to the circuit shown in Figure lB.
The output of difference signal generator 152 is coupled to tone control 154 shown in Figure 4B. The tone control 154 comprises a three stage circuit having high, mid, and low range stages 502, 504, and 506, respectively, disposed in a standard tone control topology wherein the low-range portion S06 is configured as a low-pass equalizer, the high frequency stage 502 is configured as a high-pass equalizer and the mid-range stage 504 is configured as a simple band-pass equalizer. The high frequency stage 502 comprises resistor 510, potentiometer 514, resistors 516 and S18 and capacitors 512, 520 which are selected to provide a variable band pass frequency ;
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203~79 response ranging from approximately 5KHz-20KHz, based on the position of variable resistor 514, with an approximate center fre~uency of approximately lOKHz and a boost of approximately l/-13dB. Mid-range stage 504 includes resistor 522, potentiometer 524, resistors 526 and 524 and capacitors 528, 532 which are selected to provide a variable bandpass frequency response ranging from approximately 300Hz-5KHz, based on the position of variable resistor 524, with a center frequency of approximately 2KHz and a boost of approximately +/-13db.
The low-frequency stage 506 comprises resistors 534, 538, and 544, potentiometer 536 and capacitors 540, 541 which are selected to provide a a variable frequency response ranging from approximately 20Hz-300Hz, based on the position of variable resistor 536, with a center frequency of approximately 40Hz and a boost of approximately +/-21dB. The output stage of tone control 154 is formed by operational amplifier 508 which is disposed with its non-inverting input coupled to system ground. A stabilizing filter capacitor 509 is coupled between the output and inverting input of operational amplifier 508. The outputs of the respective stages 502, 504, and 506 are coupled to the inverting input of operational 508 which outputs a selectively filtered, .5(R-L) difference signal to the level control 156 shown in Figure 4B.
Referring now to Figure 4C, the output of tone control 154 is coupled to the input of l-evel control 156.
The level control 156 is essentially identical to the level control 106, with the exception that the values of 30 resistors 262' and 294' are modified to vary the gain of VCA 266' from 0-3. As in level control 106, a current to voltage converter 290' converts the current output of VCA
266' to a voltage signal processed by the remainder of the ~,i system 150. The output of current-to-voltage converter - 35 290' is coupled to inverting buffer amplifier 158 which inverts the phase of output of level control 156 to generate the right channel (L-R) ambience signal.
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Inverting buffer amplifier 158 is a simple amplification stage including operational amplifier 560, gain control resistors 562, 564 and stabilizing capacitor 566.
Summing amplifiers 112', 114' are essentially identical to the summing means 112, 114, with the addition of input resistors 568, 570 which couple the left and right channel ambience signals to the summing nodes of the respective summing amplifiers. Specifically, the input of summing amplifier 114' is coupled to the output of buffer amplifier 158 (which comprises the right channel ambience signal) through resistor 570, and the input of summing amplifier 112' is coupled to the output of current-to-voltage converter 290' (which comprises the ; right channel ambience signal) through resistor 568.
15 Therefore, the signals present on terminals 338', 358' comprise the left and right side channel signal with a variable amount respective left and right ambience signals summed therewith, and a portion of the L+R center channel signal cancelled therefrom.
Figure 4D is a schematic diagram of a remote control voltage source used for controlling the gain of VCA's 266, 266' through terminals 274, 274', respectively.
The operation of remote control voltage source 277 is identical to remote control voltage source 275 with the exception that an identical switching network comprising potentiometer 408', resistor 406' diodes 388' and 400' and capacitor 410' is coupled in parallel the corresponding components in remote control 275 to generate the control voltage on terminal 274'.
In summary, an improved audio system for use in ` an automotive environment has been described. The present invention provides means for deriving a center channel of audio information in a stereophonic audio system wherein the center channel is used as a monophonic signal re-- 35 locator to provide an optimized sound field over a wide area. In addition, a variable portion of the monophonic information output in the center channel is cancelled from , .
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the respective side channels to maintain the overall monophonic information in the sound field at a constant level. In yet another embodiment of the present invention, a side channel difference signal is derived to generate left and right ambience signals wherein a variable amount of ambience signal may be injected in the side channels and used in conjunction with the center channel to achieve a desired effect. While the present invention is disclosed as being primarily designed for use in an automobile, those skilled in the art will appreciate that the principles disclosed herein may be applied to virtually any audio system regardless of the available listening environment. Accordingly, other uses and modifications of the present invention will be apparent to lS persons of ordinary skill in the art without departing from the spirit and scope of the present invention and all of such uses and modifications are intended to fall within the scope of the appended claims.
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Br ef Description of the Drawinas These and objects will be readily apparent to persons of ordinary skill through the detailed description of the invention below and the accompanying drawings in which:
Figure lA is a block diagram of the improved audio system of the present invention.
Figure lB is a block diagram of an alternate embodiment of the present invention.
Figure 2 is a diagram of one possible transducer arrangement in an automotive listening environment in accordance with the principles of the present invention.
Figure 3A is a schematic diagram of a portion of the system of Figure lA.
Figure 3B is a schematic diagram of another portion of the system of Figure lA.
Figure 3C is a schematic diagram of ~ circuit for remotely controlling the system of Figure lA.
20Figure 4A is a schematic diagram of a portion of the system of Figure lB.
Figure 4B is a schematic diagram of another portion of the system of Figure lB.
Figure 4C is a schematic diagram of yet another portion of the system of Figure lB.
Figure 4D is a schematic diagram of a circuit for remotely controlling the system of Figure lB.
Detailed Descri~tion of the Invention 30Figure 1 is a block diagram of the preferred embodiment of the present invention. In the system 100, first and second channels of audio information, typically referred to as left and right side channels, are coupled to a summing means 102 which generates a co~bined left plus right (L+R) audio signal. In the preferred practice of the present invention the summing means 102 limits the gain of the combined L+R audio signal to .5. The output , . ' `~' ;
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of summing means 102 is coupled to high pass filter 104 which blocks low frequency information in the combined L+R
audio signal. The high pass filter 104 is preferably a conventional highly damped Bessel slope filter having a S slope of approximately -18dB/oct. The output of high pass ; filter 104 is coupled to level control 106 which adjusts the gain of the combined L+R audio signal to limit the level of monophonic information in the center channel to a desired amount. The output of level control 106 is coupled to a level matching network 108 which allows the overall gain of the combined L+R audio signal to be ad~usted to match the sensitivity of the output components used in the left and right side channels.
The output of level control 106 is further coupled to phase inverter 110 which shifts the phase of the combined L+R audio signal by 180 degrees. The output of phase inverter 110 is further coupled to summing means 112, 114 which sums the inverted, gain limited, high pass filtered L+R audio signal with the respective left and right side channel signals to remove a portion of the monophonic center channel information from the left and right side channels, thus providing and maintaining a constant level of monophonic information in the overall sound field. While the system 100 is shown as 2S incorporating an inverter 110, those skilled in the art will appreciate that the inverter 110 may be incorporated in summing means 112, 114 by providing summing means with inverting and non-inverting inputs.
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The relationship of the respective center and side channels of the system 100 is defined by the following equations:
' L s L - K(L+R) R - R - K(L+R) C = 2K(L+R) .
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2~33679 where:
L = left side signal R = right side signal K = monophonic cancellation gain (limited to K=.5) 2K = center channel output gain In practice, the variable gain center channel provides the following output relationships:
CENTER K LEFT RIGHT CENTER SEPARATION
SETTING CHANNEL CHANNEL CHANNEL LIMIT
0% O L R O MAX
50~ .25.875L .875R .25(L+R) 17dB
-.125R -.125L
100% .5.72L .75R .5 (L+R) s.5dB
-.25R -.25L
200% 1.5L-.5R .5R-.5L L+R OdB
(limit) Referring now to Figure lB, in another embodiment of the present invention, the system 150 includes means for controlling the "ambience" of a sound field. For the sake of clarity in the description below, ; 30 items which perform identical functions bear identical designations. An ambience signal may be thought of as a side channel difference signal wherein the frequency response of the difference signal may be modified. After processing, the ambience signal is injected into the left and right side channels in a variable amount to achieve a desired effect. In practice, the ambience signal for the left side channel comprises a (L-R) difference signal and ambience signal for the right side channel comprises a (R-L) difference signal. In the system 150, a left minus right (R-L) signal is derived by difference signal generator 152. In the preferred practice of the present 203367~
invention, the gain of the difference signal generator 152 is limited to .5 to prevent clipping distortion of maximum amplitude input signals at the difference amplifier output. The output of difference signal generator 152 is coupled to tone control 154 which alters the frequency response of the difference signal. The output of tone control 154 is coupled to level control 156 which controls the amount of ambience signal added to the respective left and right side channel signals. The output of level control 156 is coupled to an inverter circuit 158 which generates the right minus left (R-L) ambience signal. The system 150 incorporates three input summing circuits 112', 114' which are essentially identical to summing circuits 112, 114 with the addition of an additional input. In the system 150, the center channel signal is derived in an identical manner as the system 100. The processed left and right side channel signals are generated in a similar manner as the system 100 wherein summing circuit 112' sums the output of inverter 110 (which comprises the inverted or phase shifted center channel signal), the left side channel signal, and the L-R ambience signal.
Similarly, the summing circuit 114 sums the output signals of inverter 110, inverter 158 (which comprises the R-L
ambience signal) and the right side channel signal. The following equations define the relationships between the ~nput and output signals in the system 150.
; C = K(.5L+.SRI
L = (.SJL - .5JR) - K(.5L~.5R) = L - K(.5L + .5R) R s (.5JR - .5JL) - K(.5L+.5R) = R - K(.5R - .5L) ~' where:
C = center signal L = left side signal R = right side signal X = monophonic cancellation gain (limited to K =
.5(K= 0 - 5)) ,. ~ ,' ... ,. ~ -. - ~
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i J = ambience injection gain (J= (0-3)) A typical installation for the improved audio system of the present invention is shown in Figure 2. In S the installation 200, the system 100 typically receives audio left and right input signals from an audio source (not shown) such as the output of a cassette deck, compact disk player, tuner, etc. Depending on the specific application, other components such as an equalizer or a 10 preamplifier may be inserted in series between the audio source and the system 100. The system 100 processes the left and right input signals to generate left side channel, right side channel and center channel signals which are amplified by power amplifiers 162-166, 15 respectively. Transducers 168, 170, coupled to the respective outputs of power amplifiers 162, 170 are typically of the same size and sensitivity and would typically be mounted in the doors, side panels, or rear deck of automobile 172. However, in an automobile, 20 options for locating a center channel transducer are quite limited. Therefore, the present invention contemplates the use oS a frequency limited center channel to allow a reduced size transducer 174 which may be mounted in a variety of locations such as an automobile dashboard where 25 space is limited. The present invention further provides a variable gain center channel so that the sensitivity of transducer 174 can be compensated to match the sensitivity of transducers 168, 170.
As can be seen in Figure 2, without the center 30 channel transducer 174, each of the passengers in automobile 172 is located in a position proximate a single side channel transducer. Thus, stereophonic imaging is minimized since each listener primarily hears the side channel closest to the listener. With the addition of the 35 side channel transducer 174, a portion of the signal from each of the side channels is relocated to the center of .
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the automobile 172 thus improving the image perceived by both passengers.
Referring now to Fiqure 3A, the system 100 receives left and right audio signals at terminals 202, 204, respectively. Input filters 206, 208, coupled to terminals 202, 206, respectively, provide noise filtering and input isolation. Input filter 206 comprises operational amplifier 218 which is disposed with an inverting input coupled to input terminal 202 through a broad bandpass filter formed by resistors 203, 207, and 214, and capacitors 205 and 210. Gain control feedback resistor 209 and filter capacitor 211 are connected in parallel between the output and the inverting input of operational amplifier 218. Input filter 208 is identical to input filter 206 and it includes resistors 213, 216, 217, 221, capacitors 212, 215, 223 and amplifier 220. The respective components of input filters 206, 208 are selected to provide a bandpass filter response of approximately lHz-200KHz.
The outputs of input filters 206, 208 comprise inverted left and right (-L,-R) input signals which are coupled to inverting summing network 102. Summing network 102 generates a composite (L~R) sum signal of the inverted left and right input signals. Summing network 102 includes resistors 222, 224, resistor 226, capacitor 230 and operational amplifier 228 wherein summing network 102 is configured to provide a gain of approximately .5.
Summing network 102 provides a relatively low impedance to the input sources to minimize distortion and to scale the input voltage to preserve the dynamic range in the system.
The output of summing network 102 is coupled to a voltage follower 103 which comprises operational amplifier 232 and resistors 234, 235. Voltage follower 103 reduces the gain of the composite L+R signal to compensate for the gain in following stages. The output of voltage follower 103 is coupled to the input of high pass filter 104 through coupling and filter capacitor 242.
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High pass filter 104 blocks any low frequency information in the composite L+R signal.
The high pass filter 104 is preferably configured as a 3rd order steep slope bessel type filter having a slope of approximately 18 dB/oct. High pass filter 104 comprises operational amplifier 240, resistor 244, and capacitors 242, 246; and operational amplifier 250, resistors 252, 254, 256, capacitor 258 and stabilizing capacitor 260. In the preferred practice of the present invention, resistors 244, 248, 256 may be of the switc~able dip resistor network type to adapt the frequency response of the system loo for use with virtually any type of transducer and amplifier system. In the preferred practice of the present invention, the components are preferably selected to provide a cutoff frequency which may range from 20-350 Hz depending on the values of resistors 244, 248 and 256 with the frequency being chosen based on the low frequency characteristics of the center channel transducer.
Referring now to Figure 3B, the output of high pass filter 104 is coupled to the input of level control 106 through voltage-to-current converting resistor 262 and AC coupling capacitor 264 which is selected to pass any AC
signal above lOHz without any significant attenuation.
Level control 106 preferably comprises a 2150A voltage controlled amplifier (VCA) 266, manufactured by That Corporation, 15 Strathmore Rd., Natick, MA 01760. VCA
266 receives the current signal generated by resistor 262 and amplifies the current signal under the control of the voltage produced across resistors 268, 2io which form a 1:50 voltage divider. The voltage produced across resistors 268, 270 is controlled by NPN transistor 272 which is disposed with its emitter coupled to one terminal of resistor 270 and its collector coupled to the V+
positive voltage source. The base of transistor 272 is coupled to control terminal 274 through resistor 276 wherein the voltage on control terminal 274 controls the 203~7~
voltage generated across resistors 268, 270, and thus the gain of VCA 266. The control signal on terminal 274 is filtered by capacitors 278, 280 and resistor 282. VCA 266 preferably provides a gain sensitivity of 6mv/dB.
Therefore, the signal present on control terminal preferably varies from 0-6 volts, thus providing a variable voltage of approximately 0-60mv across resistor 268. This voltage scaling provides a relatively low impedance at control terminal 274 and minimizes the effect of any noise present at control terminal 274. It should be noted that as the voltage across resistor 268 increases, the gain of VCA 266 decreases The present invention contemplates the use of a +/-15 volt power supply to provide ample dynamic range capabilities in the system 100. The -15v voltage source is coupled to VCA 266 through resistor 285 and is adjusted to set the quiescent operating current of VCA 266. In addition, the adjustable voltage divider formed by resistors 284, 286, and variable resistor 288 is adjusted to compensate for symmetry irregularities in the output signal of VCA 266.
The control voltage coupled to control terminal 274 may be generated by virtually any type of voltage source. In the preferred practice it is anticipated that system lOO may be located remotely from a listener. For example, in an automobile, sound systems are frequently located in the trunk of the automobile. Since the present invention anticipates the use of a variable gain center channel, it is anticipated that the control terminal 274 may be coupled to a remote voltage source 275 which may be installed in the passenger compartment of an automobile. One remote voltage source adapted for use with the present invention is shown in Figure 3C. The remote voltage source 275 comprises a switch 386 having terminals 390, 392 and 394, diodes 388, 400, light emitting diode 402, resistors 404, 406, poteniometer 408 and filter capacitor 410. Resistor 406 and poteniometer 408 are coupled in series between the V+ power supply and :
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form a variable voltage divider 412 with the output of voltage divider 412 coupled to control terminal 274 through protection diode 400.
Terminal 390 of switch 386 is also coupled to the V+ power supply. When terminals 390 and 392 of switch 386 are coupled together, the V+ power supply is coupled to terminal 274 through protection diode 388. This forces transistor 272 to conduct fully, thus forcing VCA 266 into a minimum gain state, effectively disabling the system 100. When terminals 392 and 394 of switch 386 are coupled together, the V+ power supply is coupled to ground through light emitting diode 402 and resistor 206. This illuminates light emitting diode 402 and allows the voltage on terminal 274 to depend on the position of the wiper of potentiometer 408, thereby providing adjustable gain in VCA 266.
Referring again to Figure 3B, the oùtput of VCA
266 is coupled to current-to-voltage converter 290 which comprises operational amplifier 292, feedback resistor 294 and stabilizing capacitor 296. Current-to-voltage converter 290 converts the current signal output by VCA
266 into a voltage signal processed by the remainder of the system 100. The output of current-to-voltage converter 290 is coupled to the non-inverting input of center level match circuit 108, and the inverting inputs o~ summing amplifiers 112, 114 through resistors 332, 352, respectively.
Center level match 108 provides a nominal gain of 2 and may be adjusted +/- 15 db to match the system lO0 ~D ~V Y~ ~p~ n~ ~p~x~ ~y~e~s ~ic~ ~y ~e ~se~
with t~e system ~D0, F~r examp~e~ in many syste~s, ~arge speakers and amplifiers may be utilized for t~e left and right side channels. However, since the center c~annel is high pass filtered, a smaller transducer may be used in the center cbannel. ~he nominal gain of the center channel match 108 is set at 2 so that the overall gain of the center channel composite signal is unity with the side ~.
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channel signal cancellation limited to a gain of .5. The center channel match 108 may be adjusted to compensate for difference in the sensitivity in the components used in the center and side channels thus providing a balanced sound field in the listening environment. The center channel match 108 includes operational amplifier 300 wherein the non-inverting input of operational amplifier 300 is coupled to the output current-to-voltage converter 290 through resistor 298. Gain setting resistors 312, 314, 316 are selected to set the nominal gain of operational amplifier 300 at 2. Capacitor 310 provides high frequency filtering of the output of operational amplifier 300 to stabilize the amplifier 300. A
potentiometer 304 is coupled between the respective input 15 terminals of operational amplifier 300 and its wiper i5 commected to ground through resistor 306 and AC coupling capacitor 308. Potentiometer 304 causes either the input signal or the feedback signal to be partially shunted to ground thereby providing a plus or minus 15dB gain 20 ad~ustment of the signal at the output of the amplifier 300. The potentiometer 304 has a center detent to set the gain to 2 (i.e. 6dB). The output of operational amplifier 300 is coupled to the center channel output terminal 318 through resistor 320 and AC coupling capacitor 322.
25 Capacitor 324 filters noise on center channel output terminal 318. Load resistor 326 provides a discharging path for capacitor 322.
The summing amplifiers 112, 114 are configured as inverting amplifiers which sum the combined L+R center 30 channel signal with the respective inverted left and right side channel signals to eliminate any additional monaural information from being added to the overall sound field.
As noted above, the amount of L+~ center channel signal ;cancelled from the side channels is user selectable and is 35 controlled by level control 106. In the preferred practice of the present invention, the maximum side channel cancellation is limited to .5, thus providing a r `' ' ` ~ : '~ ' 203367~
minimum center channel separation of 9.5 DB. center channel separation improves at lesser levels of cancellation.
The inverted output signal of summing amplifiers 112, 114 comprise the left and right side channel signals defined by the equations set forth above. The summin~
amplifier 112 comprises operational amplifier 330 wherein the inverting input of operational amplifier 330 is coupled to the output of current-to-voltage converter 290 through resistor 332 and to the output of input filter 102 through resistor 333. The non-inverting input of operational amplifier 330 is coupled to system grounds.
Gain setting resistor 334 and stabilizing filter capacitor 336 are connected in parallel between the inverting input and output of operational amplifier 330. The output of operational amplifier 330 is coupled to the left side channel output terminal 338 through series resistor 340 and AC coupling capacitor 342. Capacitor 344 filters out noise on channel output terminal 338. Load resistor 346 provides a discharging path for capacitor 344. Similarly, The summing amplifier 112 comprises operational amplifier 350 wherein the inverting input of operational amplifier 350 is coupled to the output of current-to-voltage converter 290 through resistor 352 and to the output of input filter 208 through resistor 353. The non-inverting input of summing amplifier 114 is coupled to system ground. Gain setting resistor 354 and stabilizing filter capacitor 356 are connected in parallel between the inverting input and output of operational amplifier 350.
~he output of operational amplifier 350 is coupled to the right side channel output terminal 358 through series resistor 360 and AC coupling capacitor 362. Capacitor 364 filters noise on right channel output terminal 358. Load resistor 366 provides a discharging path for capacitor 364.
Referring now to Figure 4A, a portion of the ~ system 150 is shown in schematic form. For the sake of :
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clarity, components which perform identical functions in the system 100 bear identical designations and are not further discussed below. In addition to the circuitry of system 100, the system 150 includes difference signal S generator 152 for deriving the difference between the left and right input signals. Difference signal ~enerator 152 includes operational amplifier 502 which is disposed with its inverting input coupled to the output of input filter 206 (which comprises the -L input signal) through resistors 504, 506, and its non-inverting input coupled to the output of input filter 20~ (which comprises the -R
input signal) through resistors 508, 510. Filter capacitor 514 and load resistor 512 are coupled in parallel between the non-inverting input of operational amplifier 502 and system ground. Feed~ack resistor 516 and stabilizing filter capacitor 518 are coupled in parallel between the inverting input and output of operational amplifier 502. While the difference signal generator 152 is coupled to -R and -L input signals, in practice, by virtue of the input phasing, the output of difference signal circuit 152 comprises a L-R difference signal. While various signal inversions may oacur during the detailed operation of the circuitry of Figures 4A-4D, the circuit remains functionally equivalent to the circuit shown in Figure lB.
The output of difference signal generator 152 is coupled to tone control 154 shown in Figure 4B. The tone control 154 comprises a three stage circuit having high, mid, and low range stages 502, 504, and 506, respectively, disposed in a standard tone control topology wherein the low-range portion S06 is configured as a low-pass equalizer, the high frequency stage 502 is configured as a high-pass equalizer and the mid-range stage 504 is configured as a simple band-pass equalizer. The high frequency stage 502 comprises resistor 510, potentiometer 514, resistors 516 and S18 and capacitors 512, 520 which are selected to provide a variable band pass frequency ;
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203~79 response ranging from approximately 5KHz-20KHz, based on the position of variable resistor 514, with an approximate center fre~uency of approximately lOKHz and a boost of approximately l/-13dB. Mid-range stage 504 includes resistor 522, potentiometer 524, resistors 526 and 524 and capacitors 528, 532 which are selected to provide a variable bandpass frequency response ranging from approximately 300Hz-5KHz, based on the position of variable resistor 524, with a center frequency of approximately 2KHz and a boost of approximately +/-13db.
The low-frequency stage 506 comprises resistors 534, 538, and 544, potentiometer 536 and capacitors 540, 541 which are selected to provide a a variable frequency response ranging from approximately 20Hz-300Hz, based on the position of variable resistor 536, with a center frequency of approximately 40Hz and a boost of approximately +/-21dB. The output stage of tone control 154 is formed by operational amplifier 508 which is disposed with its non-inverting input coupled to system ground. A stabilizing filter capacitor 509 is coupled between the output and inverting input of operational amplifier 508. The outputs of the respective stages 502, 504, and 506 are coupled to the inverting input of operational 508 which outputs a selectively filtered, .5(R-L) difference signal to the level control 156 shown in Figure 4B.
Referring now to Figure 4C, the output of tone control 154 is coupled to the input of l-evel control 156.
The level control 156 is essentially identical to the level control 106, with the exception that the values of 30 resistors 262' and 294' are modified to vary the gain of VCA 266' from 0-3. As in level control 106, a current to voltage converter 290' converts the current output of VCA
266' to a voltage signal processed by the remainder of the ~,i system 150. The output of current-to-voltage converter - 35 290' is coupled to inverting buffer amplifier 158 which inverts the phase of output of level control 156 to generate the right channel (L-R) ambience signal.
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Inverting buffer amplifier 158 is a simple amplification stage including operational amplifier 560, gain control resistors 562, 564 and stabilizing capacitor 566.
Summing amplifiers 112', 114' are essentially identical to the summing means 112, 114, with the addition of input resistors 568, 570 which couple the left and right channel ambience signals to the summing nodes of the respective summing amplifiers. Specifically, the input of summing amplifier 114' is coupled to the output of buffer amplifier 158 (which comprises the right channel ambience signal) through resistor 570, and the input of summing amplifier 112' is coupled to the output of current-to-voltage converter 290' (which comprises the ; right channel ambience signal) through resistor 568.
15 Therefore, the signals present on terminals 338', 358' comprise the left and right side channel signal with a variable amount respective left and right ambience signals summed therewith, and a portion of the L+R center channel signal cancelled therefrom.
Figure 4D is a schematic diagram of a remote control voltage source used for controlling the gain of VCA's 266, 266' through terminals 274, 274', respectively.
The operation of remote control voltage source 277 is identical to remote control voltage source 275 with the exception that an identical switching network comprising potentiometer 408', resistor 406' diodes 388' and 400' and capacitor 410' is coupled in parallel the corresponding components in remote control 275 to generate the control voltage on terminal 274'.
In summary, an improved audio system for use in ` an automotive environment has been described. The present invention provides means for deriving a center channel of audio information in a stereophonic audio system wherein the center channel is used as a monophonic signal re-- 35 locator to provide an optimized sound field over a wide area. In addition, a variable portion of the monophonic information output in the center channel is cancelled from , .
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2~3367~
the respective side channels to maintain the overall monophonic information in the sound field at a constant level. In yet another embodiment of the present invention, a side channel difference signal is derived to generate left and right ambience signals wherein a variable amount of ambience signal may be injected in the side channels and used in conjunction with the center channel to achieve a desired effect. While the present invention is disclosed as being primarily designed for use in an automobile, those skilled in the art will appreciate that the principles disclosed herein may be applied to virtually any audio system regardless of the available listening environment. Accordingly, other uses and modifications of the present invention will be apparent to lS persons of ordinary skill in the art without departing from the spirit and scope of the present invention and all of such uses and modifications are intended to fall within the scope of the appended claims.
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Claims (17)
1. An improved audio system comprising:
input means for inputting first and second audio signals;
first summing means for generating a sum signal comprising the sum of said first and second audio signals and for generating a first output signal;
inverting means coupled to said first summing means for generating a phase inverted sum signal;
second summing means coupled to said first audio signal and said phase inverted sum signal for generating a second output signal corresponding to the difference between said first audio signal and said sum signal; and third summing means coupled to said second audio and said phase inverted sum signal for generating a third output signal corresponding to the difference between said second audio signal and said sum signal.
input means for inputting first and second audio signals;
first summing means for generating a sum signal comprising the sum of said first and second audio signals and for generating a first output signal;
inverting means coupled to said first summing means for generating a phase inverted sum signal;
second summing means coupled to said first audio signal and said phase inverted sum signal for generating a second output signal corresponding to the difference between said first audio signal and said sum signal; and third summing means coupled to said second audio and said phase inverted sum signal for generating a third output signal corresponding to the difference between said second audio signal and said sum signal.
2. The improved audio system of claim 1 further including means for limiting the gain of said sum signal to .5 to preserve substantially all perceptible directional information in said second and third output signals.
3. The improved audio system of claim 1 further including variable gain means for controlling the gain of said first output signal.
4. The apparatus of claim 1 wherein said first output signal comprises a center channel of audio information.
5. The apparatus of claim 1 wherein said second output signal comprises a right side channel of audio information.
6. The apparatus of claim 1 wherein said second output signal comprises a left side channel of audio information.
7. The improved audio signal of claim 1 further including high pass filter means for limiting the frequency range of said first output signal.
8. The improved audio system of claim 1 further including means for adjusting the gain of said first summing means to match the sensitivity of the center and side channel output components.
9. An improved audio system comprising:
input means for inputting first and second audio signals;
first summing means for generating a sum signal comprising the sum of said first and second audio signals and for generating a first output signal;
second summing means having inverting and non-inverting inputs wherein said non-inverting input is coupled to said first audio signal and said inverting input is coupled to said sum signal said second summing means for generating a second output signal; and third summing means having inverting and non-inverting inputs wherein said non-inverting input is coupled to said second audio signal and said inverting input is coupled to said sum signal said third summing means for generating a third output signal.
input means for inputting first and second audio signals;
first summing means for generating a sum signal comprising the sum of said first and second audio signals and for generating a first output signal;
second summing means having inverting and non-inverting inputs wherein said non-inverting input is coupled to said first audio signal and said inverting input is coupled to said sum signal said second summing means for generating a second output signal; and third summing means having inverting and non-inverting inputs wherein said non-inverting input is coupled to said second audio signal and said inverting input is coupled to said sum signal said third summing means for generating a third output signal.
10. An improved audio system comprising:
inverting input means for inputting first and second audio signals and outputting inverted first and second audio signals;
first summing means for generating a sum signal comprising the sum of said inverted first and second audio signals;
inverting means for inverting the phase of said sum signal;
second summing means coupled to said inverted first audio signal and said phase inverted sum signal for generating a second output signal; and third summing means coupled to said inverted second audio and said phase inverted sum signal for generating a third output signal.
inverting input means for inputting first and second audio signals and outputting inverted first and second audio signals;
first summing means for generating a sum signal comprising the sum of said inverted first and second audio signals;
inverting means for inverting the phase of said sum signal;
second summing means coupled to said inverted first audio signal and said phase inverted sum signal for generating a second output signal; and third summing means coupled to said inverted second audio and said phase inverted sum signal for generating a third output signal.
11. An improved audio system comprising;
input means for inputting first and second channels of audio information;
first summing means for generating a sum signal comprising the sum of said first and second channels of audio information and for generating a first output signal;
inverter means coupled to said first summing means for inverting the phase of said sum signal;
second summing means coupled to said first channel of audio information and the output of said inverter means for generating a second output signal;
third summing means coupled to said second channel of audio information and the output of said first summing means for generating a third output signal;
first, second and third output amplifiers coupled to said first, second, and third output signals, respectively; and first, second, and third transducers coupled to said first second and third output amplifiers, said first, second, and third transducers comprising left, center and right channel output transducers, respectively.
input means for inputting first and second channels of audio information;
first summing means for generating a sum signal comprising the sum of said first and second channels of audio information and for generating a first output signal;
inverter means coupled to said first summing means for inverting the phase of said sum signal;
second summing means coupled to said first channel of audio information and the output of said inverter means for generating a second output signal;
third summing means coupled to said second channel of audio information and the output of said first summing means for generating a third output signal;
first, second and third output amplifiers coupled to said first, second, and third output signals, respectively; and first, second, and third transducers coupled to said first second and third output amplifiers, said first, second, and third transducers comprising left, center and right channel output transducers, respectively.
12. The apparatus of claim 11 wherein said center channel output transducer may be smaller than said left and right output transducers.
13. The apparatus of claim 11 further including means for matching the sensitivity of said center channel transducer to said left and right channel transducers.
14. An improved audio system comprising:
input means for inputting first and second audio signals;
first summing means for generating a sum signal comprising the sum of said first and second audio signals and for generating a first output signal;
difference signal means for generating a difference signal comprising the difference of said first and second audio signals;
first inverting means coupled to said first summing means for generating a phase inverted sum signal;
second inverting means coupled to said difference signal means for generating a phase inverted difference signal;
second summing means for summing said first audio signal, said phase inverted sum signal, and said difference signal and for generating a second output signal; and third summing means for summing said second audio, said phase inverted sum signal, and said phase inverted difference signal, and for generating a third output signal.
input means for inputting first and second audio signals;
first summing means for generating a sum signal comprising the sum of said first and second audio signals and for generating a first output signal;
difference signal means for generating a difference signal comprising the difference of said first and second audio signals;
first inverting means coupled to said first summing means for generating a phase inverted sum signal;
second inverting means coupled to said difference signal means for generating a phase inverted difference signal;
second summing means for summing said first audio signal, said phase inverted sum signal, and said difference signal and for generating a second output signal; and third summing means for summing said second audio, said phase inverted sum signal, and said phase inverted difference signal, and for generating a third output signal.
15. An improved method for generating a multi-dimensional sound field comprising the steps of:
inputting first and second channels of audio information;
summing said first and second channels of audio information to generate a combined audio signal;
limiting the gain of said combined audio signal to generate a gain limited combined audio signal;
inverting said gain limited combined audio signal;
summing said gain limited inverted combined audio signal with said first channel of audio information to generate a first output channel of audio information;
summing said gain limited inverted combined audio signal with said second channel of audio information to generate a second output channel of audio information;
amplifying said gain limited audio signal to generate a third output channel of audio information;
outputting said first and second and third channels of audio information wherein said third channel audio information comprises a center channel.
inputting first and second channels of audio information;
summing said first and second channels of audio information to generate a combined audio signal;
limiting the gain of said combined audio signal to generate a gain limited combined audio signal;
inverting said gain limited combined audio signal;
summing said gain limited inverted combined audio signal with said first channel of audio information to generate a first output channel of audio information;
summing said gain limited inverted combined audio signal with said second channel of audio information to generate a second output channel of audio information;
amplifying said gain limited audio signal to generate a third output channel of audio information;
outputting said first and second and third channels of audio information wherein said third channel audio information comprises a center channel.
16. The method of claim 15 wherein the gain of said combined audio signal is limited to .5.
17. An improved method of generating a multi-dimensional sound field, comprising:
providing a left channel signal and a right channel signal;
combining said left channel signal and said right channel signal into a center channel signal;
adjusting the amplitude of said center channel signal to provide a center channel output signal;
subtracting a signal corresponding to said center channel output signal from said left channel signal to provide a left channel output signal;
subtracting a signal corresponding to said center channel output signal from said right channel signal to provide a right channel output signal.
providing a left channel signal and a right channel signal;
combining said left channel signal and said right channel signal into a center channel signal;
adjusting the amplitude of said center channel signal to provide a center channel output signal;
subtracting a signal corresponding to said center channel output signal from said left channel signal to provide a left channel output signal;
subtracting a signal corresponding to said center channel output signal from said right channel signal to provide a right channel output signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US461,186 | 1990-01-05 | ||
| US07/461,186 US5113447A (en) | 1990-01-05 | 1990-01-05 | Method and system for optimizing audio imaging in an automotive listening environment |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2033679A1 true CA2033679A1 (en) | 1991-07-06 |
Family
ID=23831545
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002033679A Abandoned CA2033679A1 (en) | 1990-01-05 | 1991-01-07 | Method and system for optimizing audio imaging in an automotive listening environment |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US5113447A (en) |
| CA (1) | CA2033679A1 (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4893342A (en) * | 1987-10-15 | 1990-01-09 | Cooper Duane H | Head diffraction compensated stereo system |
| ES2149235T3 (en) * | 1993-01-22 | 2000-11-01 | Koninkl Philips Electronics Nv | DIGITAL TRANSMISSION IN 3 CHANNELS OF STEREOPHONIC SIGNALS LEFT AND RIGHT AND A CENTRAL SIGNAL. |
| US5491753A (en) * | 1993-11-22 | 1996-02-13 | Chrysler Corporation | Method and device for testing for audio induced sympathetic buzzes |
| US6311155B1 (en) * | 2000-02-04 | 2001-10-30 | Hearing Enhancement Company Llc | Use of voice-to-remaining audio (VRA) in consumer applications |
| US6442278B1 (en) * | 1999-06-15 | 2002-08-27 | Hearing Enhancement Company, Llc | Voice-to-remaining audio (VRA) interactive center channel downmix |
| US6970568B1 (en) | 1999-09-27 | 2005-11-29 | Electronic Engineering And Manufacturing Inc. | Apparatus and method for analyzing an electro-acoustic system |
| JP2001268700A (en) * | 2000-03-17 | 2001-09-28 | Fujitsu Ten Ltd | Sound device |
| US7164773B2 (en) * | 2001-01-09 | 2007-01-16 | Bose Corporation | Vehicle electroacoustical transducing |
| KR100380620B1 (en) * | 2002-06-10 | 2003-04-21 | Idea & Technology Ind Co Ltd | Switching mode power supply unit based power amplifier |
| US7551745B2 (en) * | 2003-04-24 | 2009-06-23 | Dolby Laboratories Licensing Corporation | Volume and compression control in movie theaters |
| US7251337B2 (en) * | 2003-04-24 | 2007-07-31 | Dolby Laboratories Licensing Corporation | Volume control in movie theaters |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3478167A (en) * | 1965-07-12 | 1969-11-11 | Morris Sorkin | Three speaker stereophonic audio system |
| US3746792A (en) * | 1968-01-11 | 1973-07-17 | P Scheiber | Multidirectional sound system |
| US3632886A (en) * | 1969-12-29 | 1972-01-04 | Peter Scheiber | Quadrasonic sound system |
| US4747142A (en) * | 1985-07-25 | 1988-05-24 | Tofte David A | Three-track sterophonic system |
-
1990
- 1990-01-05 US US07/461,186 patent/US5113447A/en not_active Expired - Lifetime
-
1991
- 1991-01-07 CA CA002033679A patent/CA2033679A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| US5113447A (en) | 1992-05-12 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| FZDE | Discontinued |