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Publication numberUS3476863 A
Publication typeGrant
Publication dateNov 4, 1969
Filing dateOct 7, 1965
Priority dateOct 7, 1965
Publication numberUS 3476863 A, US 3476863A, US-A-3476863, US3476863 A, US3476863A
InventorsDonald J Campbell
Original AssigneeChicago Musical Instr Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Conversion of tonal character of aural signals
US 3476863 A
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Description  (OCR text may contain errors)

CONVERSION OF TONAL CHARACTER 0F AURAL SIGNALS Filed Oct. '2, 1965 D. J. CAMPBELL Nov. 4, 1969 5 Sheets-Sheet l M 2 IL 3 (V I T L I F 1 o I T 2 A Ah h 4 88 mm m Im L m 4 H A S T. I I I N E M L G C P I 0 U N M S R A P u 5 m l K n u P m 1 U! W m H M/VE/VTOR DONALD J. CAMPBELL '8'A a'n IG'CI SIGNAL.

PROCESSING UNIT PICKUP ATTORNEYS 1969 D. J. CAMPBELL CONVERSION OF TONAL CHARACTER OF AURAL SIGNALS Filed Oct. 7, 1965 5 Sheets-Sheet 2 INVENTOR DONALD J. CAMPBELL A TTORIVYS Nov. 4, 1969 D. J. CAMPBELL 3,476,863

couvmns on OF TONAL CHARACTER OF AURAL SIGNALS Filed Oct. 7, 1965 5 Sheets-Sheet 3 536 527 m m I529 50l FIG. 3

5m, INVENTOR PW, Md? //V 4 ATTORNEYS Nov. 4, 1969 D, J. CAMPBEL 3,476,863

CONVERSION OF TONAL CHARACTER OF AURA L SIGNALS Filed Oct. '7, 1965 5 Sheets-Sheet 4 70; N 4 MVEWOR DONALD J. CAMPBELL Nov. 4, 1969 D. J. CAMPBELL 3,476,863

v CONVERSION OF TONAL CHARACTER 0F AURAL SIGNALS Filed Oct. 7. 1965 5 Sheets-Sheet 5 INVENTOR DONALD J. CAMPBELL FWJW 4w ATTORNEYS United States Patent O 3,476,863 CONVERSION OF TONAL CHARACTER OF AURAL SIGNALS Donald J. Campbell, Cincinnati, Ohio, assignor to Chicago Musical Instrument Co., Lincolnwood, 11]., a corporation of Delaware Filed Oct. 7, 1965, Ser. No. 493,773 Int. Cl. G10h 1/00; H03k 5 /01 US. Cl. 841.01 30 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to the art of electronic music generation. More particularly, this invention is concerned with the conversion of an aural input of one s t tone color or timbre to an aural output having a different tone color or timbre, and/ or a different pitch, or ampitude, or other characteristics. As used in the present specification and claims, unless otherwise indicated expressly or by context, the term aural input is intended to include not only the compressional sound wave per se, but also a corresponding electrical signal that may be generated concurrently with a sound wave, as for example by the use of an electromagnetic or other direct pick" up as is employed with electric guitars.

In accordance with the general aspectsof the present invention, an aural input signal is analyzed to obtain its fundamental frequency, and each cycle is analyzed to obtain its amplitude. Output waves of high harmonics content are then produced, for example square and sawtooth waves, which correspond in frequency to the fundamental of the aural input signal, and correspond cycle by cycle to the amplitude of the aural input signal. The resultant signals are then processed through well known tone color filters to obtain desired variations in the timbre of the signal, and thence arereconverted into an aural signal of desired tone color; different from that of the aural input. Further, as willbe readily apparent, the processing of the signal can include frequency doubling and dividing in order to change the pitch of the signal as desired.

The processing of an aural input signal as above described, may be used for example to convert a voice input to an instrumental output, convert an input from one instrument to an output having the tone color of a different instrument, and converting an input signal of one tone color and fundamental frequency to an output of a difierent tone color and same or different fundamental frequency, or same tone color and different fundamental frequency. 7

It is therefore among the objects of the present invention to provide: for the electronic processing'of aural input signals to aural output signals; for the conversion of an aural input signal to waves of high harmonic content having the same fundamental frequency as the input, or multiples thereof, and corresponding in amplitude to the input signal, cycle by cycle; for the conversion of an aural input signal of one tone color to an aural output signal of another tone color; and for the conversion of an aural input signal of one frequency to an aural output 3,476,863 Patented Nov. 4, 1969 ice signal of a multiple or fraction of the input frequency.

Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of one specific embodiment of the invention had in conjunction with the accompanying drawings, in which like numerals refer to like or corresponding parts, and wherein:

FIG. 1 is a block diagram of an overall system from aural input to aural output;

FIG. 2 is a schematic circuit diagram of a signal processing unit embodying the present invention; and

FIGS. 3, 4, 5, and 6 are waveform charts showing the various waveforms appearing in the processing unit of FIG. 2 in their relative time relationships.

Referring first to the block diagram of FIG. 1, it will be seen that a pickup unit 10, which may be a microphone for transducing a voice or instrumental sound to an electrical signal, transmits the input signal to the processing unit 11, where the signal is transposed into square and sawtooth waves related in frequency and amplitude to the input signal. The square and sawtooth wave outputs indicated as 4 foot, 8 foot and 16 foot outputs, are carried by busses 12 to appropriate tone color filters 13. The outputs of the filters 13 are combined in amplifier 14, and thence transmitted to output speaker 15. Obviously, any number of pickups 10 may be provided, depending upon the number of inputs utilized, as indicated in FIG. 1 by pickups and processing units numbered I through 11. Each processing unit may of course be identical, and consequently the detailed description of one such unit will be sufiicient.

Processing unit 11 is shown in the schematic circuit diagram of FIG. 2. Many of the waveforms present in the operation of the circuit of FIG. 2 have been indicated thereon to facilitate an understanding of this circuit, and they have been numbered in accordance with the waveforms in the chart of FIG. 3.

The aural input signal represented by a waveform 501 is coupled from the pickup microphone 10 through capacitor 21 to the base of clipping amplifier 22. The clipped and inverted waveform 502 constitutes the output of amplifier 22, and it contains only frequency information of input waveform 501. Waveform 502 is then differentiated by capacitor 23 and resistor 24 into wayeform 503, then rectified by diode 25 into waveform 504. It 'will be observed that at this point in processing the inputsignal 501, a trigger is provided for each negative going zero crossing of waveform 501. The positive going crossings have been eliminated by the diode 25.

Waveform 504 is converted to a sawtooth Waveform 505 by the interaction of the transistors 26 and 30, and the network of resistors 28 and 29 and capacitors 27 and 32. Between trigger pulses of waveform 504, transister 26 is biased below cutoff, thereby causing capacitor-27 to be slowly charged through resistors 28 and 29. Each trigger pulse of waveform 504 activates transistor 2i6'and causes capacitor 27 to be rapidly discharged thereth-rough, thus producing the sawtooth waveform 505. The output of the sawtooth generator is converted to a lowimpedance through emitter follower transistor 30 and anti-oscillation resistor 31. Bootstrap feedback capacit'or' 32 couples the output of emitter follower 30 to a point between resistor 28 and 29, to increase the linearity of the waveform 505.

The output 505 of emitter follower 30 is converted into a square wave, i.e. a rectangularwave symmetrical in time, by means of a squarer circuit comprising transister 33 and diode 34. When the linear sawtooth wave 505 is coupled through capacitor 35 into a load, the new D.C. level created depends on the nature of the load. If the load'is linea-r and bilateral, the new level is 524 indicated in FIG. 3, area 520 being equal to area 521, and time 522 being equal to time 523. A bilateral load is provided by diode 34 conducting during time 522 and transistor 33 conducting during time 523. A linear load is insured by providing most of the load impedance in resistor 36. These provisions result in level 524 being held at the conduction point of the base of transistor 33. Thus transistor 33 conducts during time 523, is cut off during time 522, and square wave 506 is thereby produced at the output of transistor 33. Feedback network 37 and 38 provides for transistor interchange and component tolerances. It will be observed that the symmetry of square wave 506 on the time axis is substantially independent of frequency. Also it should be noted that this symmetry of 506 is obtained despite any asymmetry that may exist in input waveform 501. This result is had by utilizing only the negative going zero crossings of input waveform 501 as obtained at 504, establishing frequency on that basis as in sawtooth waveform 505, and then dividing the frequency period into two equal halves, as in square waveform 506.

Having established a symmetrical waveform 506 equal in frequency to the fundamental frequency of the input signal, there remains to be established for each cycle of this waveform an amplitude corresponding to that of the corresponding cycle of the input signal. When controlling the amplitude of a square wave, it is not necessary to establish amplitude until one-half of a given cycle has occurred. This fact makes it possible to measure the peak of a controlling wave during each first half of the square wave cycle, to store this amplitude information, and then to use it to control the amplitude of each second half of the square wave. By clearing the storage element at the end of each cycle, the amplitude of each square wave cycle then becomes a function of the peak amplitude of the corresponding cycle of the controlling wave.

This function is accomplished by the amplitude control circuit comprising coupling capacitor 39, diode 40, storage capacitor 41, emitter follower transistor 42, resistor 43, amplifier '44, diode 45a, differentiating network of capacitor 45 and resistor 46, and transistor 47. The input waveform 501 is coupled through capacitor 39 to diode 40, which passes only the positive going portions of Waveform 501, thereby trapping the positive peak voltage of 501 on storage capacitor 41, indicated as waveform 509. The emitter follower 42 passes this waveform through resistor 43 to point 48 where it is combined with waveform 506 coupled through diode 45a. Positive portions of waveform 506 are not passed by diode 45 to point 48, hence during that portion of the cycle the positive plateau of waveform 509 controls the voltage at point 48. The negative portions of waveform 506 are passed by diode 45 to point 48, causing the voltage of waveform 509 to be dropped across resistor 43, and bringing the voltage at point 48 below cut off value for the base of transistor 44. Accordingly, waveform 510 is generated at point 48, whose amplitude for each cycle is a direct function of the peak amplitude of waveform 501 for that cycle.

Considering the amplitude control circuit with more detailed reference to the waveforms in FIG. 3, it will be seen that waveform 501 charges capacitor 41 during the time 523, resulting in the 526 portion of waveform 509. Waveform portion 526 has substantially the same shape and amplitude as the portion 527 of waveform 501, hence amplitude 530 of waveform 509 is substantially equal to amplitude 529 of waveform 501. During time 523 square wave 506 is conducted to point 48 by diode 45a lowering the base of transistor 44 below cut off. During this time voltage of waveform 509 has no effect on the transistor 44 and is dropped across resistor 43. Since diode 45a is cut off during the time 531, the voltage of waveform 509 controls, establishing the amplitude of waveform 510 at the value 530.

Waveform 510 applied to the base of amplifier 44 produces the desired square wave output signal embodied in waveform 511. Waveform 511 is differentiated by capacitor 45 and resistor 46 into waveform 512, and each positive going portion of waveform 511 produces a corresponding positive spike in waveform 512 triggering transistor 47 into momentary conduction to discharge storage capacitor 41.

The foregoing description relates to the basic flow of a signal being processed in unit 11. There remain several refinements to the processing unit that will now be de scribed. It will be recalled that generation of the basic signal of the procesing unit, i.e., waveform 506, depends upon negative going zero crossings of input signal 501, producing one square wave cycle for each such zero crossing. These negative going zero crossings are registered in the spikes of waveform 504. As illustrated in the drawings, input signal 501 has one negative going zero crossing per fundamental cycle. However, this input is usually a complex signal as illustrated by the secondary minimum at 536 in waveform 501 (see FIG. 3). As the amplitude of this input signal decreases, changes in the waveform may occur whereby a point Will be reached where the minimum point 536 crosses the Zero value, and there would thereby be produced a false or extraneous zero crossing which would immediately result in a doubling of the frequency of waveform 506. To eliminate this occurrence, a blanking signal is generated to blank out waveform 504 for most of the period between spikes, when such extraneous zero crossings are likely to occur. The blanking circuit is embodied in the feedback path between capacitor 51 and transistor 52.

Sawtooth waveform 505 is coupled through capacitor 51 to the base of transistor 50. Transistor 50 and its associated circuitry responds to the sawtooth input in the same manner as squarer 33 to produce a wave output, except the load is designed to produce the rectangular waveform 507 unsymmetrical in time, instead of the symmetrical waveform 506, with portion 532 extending for about of the time period 525. Waveform 507, after passing through a resistance-capacitance-diode network appears as waveform 508 at the base of transistor 52. The voltage level of portion 533 of waveform 508 is chosen to render transistor 52 conductive, and non-conductive or cut off at a value slightly below. As a result, the base of transistor 26 is blanked during the period 533 when transistor 52 is conductive. The shape and values of waveform 508 are selected to blank out the base of transistor 26 from approximately the 5% point to approximately the 90% point of the period 525. The margins at either end of the blanking period are necessary to assure that the fundamental signal frequency zero crossings are not also blanked out. Otherwise, the base of transistor 26 would be driven positive by the true signal zero crossing spikes of waveform 504 and simultaneously negative by transistor 52, and the system would not operate.

Network 54, 55, 56 and 57 eliminates transients 1010 and 1011 shown in the waveform diagram of FIG. 4. FIGURE 4'shows the operation of the blanking circuit under transient conditions, whereas, the above description and the waveform diagram of FIG. 3 shows its operation under steady state conditions. Waveform 1001 corresponds to sawtooth waveform 505 appearing at the output of transistor 30 when an input signal begins at instant 1007 and ends at instant 1008. Waveform 1002 appears at the base of transistor 50, and waveform 1003 corresponds to waveform 507 appearing at the collector of transistor 50. Differentiating network 54, 55 produces waveform 1004, and diode 56 passes ony the negative portion thereof, producing waveform 1005 and eliminating transients 1010 and 1011. These transients can cause frequency halving when notes are rapidly repeated; because if a second note begins during time 1009, it is possible for a true or desired zero crossing to occur during the time waveform 504 would be blanked out by transient 1010, and if just one desired or true zero crossing is blanked out the entire system must operate at half frequency thereafter for the remainder of the note, rejecting each alternate true zero crossing as an extraneous zero crossing. r l Y Waveform 1005 has a positive quiescent value which if coupled to transistor 52 would blank out the base of transistor 26 between notes and render the system unresponsive to the beginning of any note. However, passing Waveform 1005 through capacitor 59 results in waveform 1006, corresponding to waveform 508, having a quiescent value of zero. Resistor 60 adjusts the impedance to produce a very low slope for portion 533 of waveform 508, insuring effective blanking over the entire period of 533. Diode 61 clamps the low value of Waveform 508 to ground providing a more effective drive of transistor 52.

Time 1012 is the delay between the beginning of a note andthe beginning of operation of the blanking circuits. This delay does not cause any difficulty since the need for blanking always commences sometime after the beginning of a note in the type of musical or input signal under consideration. Moreover, time delay 1012 is actually an advantage in many instances where the note begins with a speaking tone or a beginning transient with contains a high portion of aperiodic components, non-harmonic components or components having a rapid shift in frequency. In these instances, delay period 1012 gives the signal time to stabilize before blanking begins, which otherwise could result in the blanking circuit following a false frequency, or otherwisemalfunctioning.

With respect to capacitor 58 in the blanking feedback network,it merely functions to produce the margin time 534 afforded by the rounded portion 535 of waveform 508.

For certain types of aural inputs to the signal processing unit 11, as for example where the input signal is of the less complex variety, i.e., is nearly sinusoidal in form, the refined system embodying the sawtooth generator, its blanking circuit, and squarer circuit may not be essential. In such instance the clipped and inverted output waveform 502 obtaindat the collector of transistor 22 may be applied directly through the diode 45a to point 48 in the amplitude control circuit, whereupon the cycle by cycle amplitude control is obtained in the same manner as above-described. For this purpose a switch 125 is provided. When it is closed to contact 125a, the aural input signal is processed through the refined circuitry including the sawtooth generator, its blanking circuit, and squarer circuit. However, when the switch 125 is closed to contact 125b, the output of transistor 22, waveform 502, is coupled directly to the diode 45. Obviously, if desired, a processing unit of lower performance characteristics could be, built, providing only the direct coupling of waveform .502 to the diode 45a, omitting the sawtooth generator, its

blanking circuit, and the squarer circuit.

As previously indicated, it is one of the principal purposes of thepresent invention to take a musical input of one character andconvert it to a musical output of another character, as for example converting the music of one instrument to that of a different instrument. To accomplish this objectivesuccessfully, it is essential that one be able to select the envelope of the signal during the processing operation, to correspond with that musical fvalue' desired at the-output. This operation is exemplified and embodied in the networks 16' and selector switch 62. When switch 62 is in the position 63, the output signal 511 is not affected, and it follows the amplitude envelope of the input signal 501. If the input were a plucked string,

the output envelope would be the same, and is illustrated ,as envelope 701 of FIG. 5. The switch position 64- produces an amplitude envelope for output waveform 511 shown in envelope 702, which has a more gradual beginning and is not as percussive as that of envelope 701. The gradual beginning is caused by capacitor 67 requiring time .to charge through diode 68 and thus lowering level 530 at the beginning of a.,note. Switch position 65 results in the envelope 703 having a flat top and sounding organlike. The flat top is caused by diode 68 being returned to a fixed voltage so that level 530 never exceeds that voltage value. Switch position 66 produces the amplitude envelope 704, which is a combination of envelopes 702 and 703. It is contemplated that when the aural input of the processing unit is an expressive musical source, position 63 would most likely be used in order to permit the expressiveness of the source to be reflected in the output. One or another of the switch positions 64, 6-5, and 66 would most likely be used to vary the musical expression of the output when the input is provided by an instrument having a fixed amplitude envelope, such for example as a guitar.

A further feature of the present processing system is a minimum input amplitude cut off circuit. Because the signal to noise ratio becomes sufiiciently low to cause erratic operation of the sawtooth wave generator 26, 27, 30, it is desirable to provide a cut off circuit operable when the input signal amplitude falls below a certain value. This result is accomplished by taking the squared input signal as waveform 502 at the collector output of transistor 22, limiting it by means of diode 71 to a certain maximum value, passing this signal through diode 73, and integrating the resultant rectified relatively negative value of the signal on capacitor 74. So long as the waveform 502 obtains an amplitude value in excess of the limiting threshold established by diode 71, the relatively negative value thereby established on capacitor 74 biases the transistor 47 below its out off value. However, when the amplitude value of waveform 502 falls below the limiting threshold of diode 71, capacitor 74 moves positive, changing the bias on the base of transistor 47 to a conducting value, thereby blanking the base of transistor 42 and rendering the amplitude control circuit inoperative and cutting off any output from the present processing unit.

Operation of this threshold cut off circuit is explained in greater detail with reference to the Waveform chart of FIG. 6. Waveform 1101 is selected to represent an input waveform, and waveform 1102 is the corresponding squared wave appearing as the output of transistor 22. At the time point 1106, the amplitude of waveform 1102 becomes too small for reliable operation of the succeeding stages. Waveform 1103 is that appearing at the negative side of diode 71 resulting from the clipping action of the diode by voltage 1107 at the positive side of diode 71. Voltage 1107 is selected so as to reduce the value of waveform 1103 to zero at time 1108-, shortly before time 1106. Waveform 1103 is passed by capacitor 72 and rectified by diode 73, producing waveform 1104 at the capacitor 74. Resistor 75 is selected to provide a positive quiescent value on the base of transistor 47, causing it to conduct and short out the signal on the base of transistor 42, thus preventing the amplitude control circuit from passing any signal. When the peak value of the input signal 1101 is such as to provide a peak value for waveform 1102 greater than the voltage value 1107, the voltage integrated on the capacitor 74 is maintained at a point where transistor 47 is cut off, permitting the amplitude control circuit to onerate normally, as previously described. Accordingly, Waveform 1105 is the amplitude envelope of the output signal waveform 511, in which portion 111.0 reflects operation of the present threshold cut off circuit, and portion 1109, in dotted line, is the tail end of envelope 1105 which would contain aperiodic signals if it were not eliminated by the present threshold cut off circuit.

Pursuant to the foregoing description there is obtained at the output of transistor 44 a symmetrical square waveform signal 511, having a frequency equal to the fundamental frequency of the input signal 501 (or 1101 in FIG. 6), and whose amplitude is a cycle by cycle function of the input signal amplitude which of course may be modified When desired by the envelope shaping networks 61. Waveform 511 is dropped in amplitude across resistor 81 foot pitch, the waveform 505 is frequency divider, as indicated at 96, and then processed in the the same manner as indicated in the present circuit by utilizing the input signal 501 as the amplitude control therefor, as indicated at 97 in FIG. 2.

vided a system for processing an aural input of one tone color, to obtain an aural output of a different character, wherein the output is related in cycle by cycle correspondence to the frequency and amplitude of the input. It is understood, of course, that the specific embodiment herein disclosed is presented only for purposes of illustrating the invention, and that modifications and variations will be apparent to those skilled in the art. Accordingly, such modifications and variations as are embraced by the spirit and scope of the appended claims are contemplated as being within the purview of the present invention.

and coupled through capacitor 82 as square waveform 511 to the appropriate tone color filter units 13.

Simultaneously, square waveform 511 is differentiated by capacitor 83 and resistor 84 to provide waveform 512. The negative spikes of this waveform are passed by diode 85 to a sawtooth generator comprising the resistance capacitance network 86, 87, 8-8 and 89. Between negative spikes of waveform 512, capacitor 86 charges to a positive value, and then is suddenly discharged by a negative spike from waveform 512, thus forming the sawtooth wave- 1 form 513. This waveform is then inverted by amplifier '91 to waveform 515, and again inverted and amplified by amplifier 92 to waveform 516. Waveform 516 is then passed to the appropriate tone color filter unit 13.

By appropriate filtering of square waveform 514 and sawtooth waveform 516, a signal of desired tone color is obtained, as is well understood in the art, and this resultant signal is then amplified at 14, and passed to the output speaker to provide an aural output.

The circuit shown in FIG. 2 is the processing circuit for an 8 foot pitch, or the reference footage having the same pitch as the input signal. To obtain the next higher octave, or 4 foot pitch, the 4 foot coupler switch 93 is closed connecting the square wave output channel 94 and point 95 in the sawtooth output channel. On closing switch 93, waveforms 514 and 515 are added, and with waveform 515 chosen to have a peak amplitude twice that of waveform 514, the output of the sawtooth channel is a sawtooth wave of double the frequency of waveforms 515 or 514. This frequency doubling action is more fully explained in my copending application, Ser. No. 474,892, filed July 26, 1965, and entitled Frequency Doubler and Coupler for Electronic Music Generation Systems.

In addition, to obtain the next lower octave, or a 16 Where multiple processing units are used, with a sep- Thus, pursuant to the present invention there is pro- What is claimed is: 1. In a system for converting an aural input signal of one tonal character to an aural output signal of a different tonal character:

(a) a processing unit comprising means for detecting a single fixed reference point in each cycle of the fundamental frequency of said input signal;

(b) said detecting means comprising means for generating a pulse for a selected direction of zero cfo'ssing for each cycle of the fundamental frequency of said input signal;

(c) said processing unit further including means responsive to said detecting means for generating a blanking signal extending from shortly after a given detecting means pulse to shortly before the next succeeding detecting means pulse to blank out extraneous detecting means zero crossing pulses that may occur during a latter portion of a complex aural input tone; and

' (d) means responsive to said detecting means for generating one cycle of a square wave signal for each of said detected fixed reference points in cycle-forcycle correspondence with the cycles of said input signal.

2. In a system for converting an aural input signal of one tonal character to an aural output signal of a different tonal character:

(a) a processing unit comprising means for detecting a single fixed reference point in each cycle of the fundamental frequency of said input signal, said detecting means comprising:

( 1) means for clipping the input signal to obtain the fundamental frequency thereof,

(2) means for differentiating the clipped signal to obtain pulses definitive of zero crossings of the input signal, and

(3) means for rectifying the differentiated signal to obtain those pulses definitive of only one selected direction of zero crossing; and

(b) means responsive to said detecting means for generating one cycle of a symmertical waveform signal for each of said detected fixed reference points in cycle for cycle correspondence with the cycles of said input signal.

3. A system according to claim 2, said generating means comprising,

(1) a sawtooth waveform generator producing one cycle in response to each of said rectified pulses, and

(2) a square waveform generator responsive to the sawtooth generator and providing a linear and bilateral load therefore producing one symmetrical square waveform cycle in response to each sawtooth waveform cycle.

4. In a system as set forth in claim 3, said unit further including a second rectangular waveform generator responsive to said sawtooth waveform generator and providing a linear and non-bilateral load therefor producing one non-symmetrical rectangular Waveform cycle in response to each sawtooth waveform cycle, means for coupling the output of said rectangular waveform generator to the output of said rectifying means during a portion of the cycle of said non-symmetrical rectangular waveform to blank out extraneous pulses that may appear in th output of said rectifying means between successive pairs of rectifying means output pulses definitive of zero crossings of the fundamental frequency of said input signal, as may occur during a latter portion of a complex aural input tone.

5. In a system as set forth in claim 3, said unit further including an amplitude control circuit comprising means for detecting the peak value of a given half of each cycle of said input signal, and means for combining said detected peak value with the corresponding cycle of said square waveform to provide a second symmetrical square waveform in cycle by cycle synchronism with the first mentioned symmetrical square waveform and having an amplitude corresponding with the peak value of the corresponding input signal cycle.

6. In a system as set forth in claim 5, said unit further including means for varying the amplitude envelope of a series of said second symmetrical square waveform cycles in accordance with a selected function.

7. In a system as set forth in claim 5, said unit further including means responsive to the amplitude of said clipped input signal for reducing to zero the amplitude of said second symmetrical square waveform when the amplitude of said clipped input signal falls below a selected value.

8. In a system as set forth in claim 7, said unit further including a first output channel coupling said second symmetrical square waveform to tone color filter means, a second output channel including means for converting said second symmetrical square waveform to a corresponding sawtooth waveform and coupling it to tone color filter means, and means for converting the outputs of said tone color filter means to sound.

9. In a system for converting an aural input signal of one tonal character to an aural output signal of a differenttonal character:

' (a) a processing unit comprising means for detecting a single fixed reference point in each cycle of the fundamental frequency of said input signal;

(b) said processing unit further including an amplitude control circuit comprising means for detecting th peak value of a given half of each cycle of said input signal;

(( means responsive to said detecting means for generating one cycle of a symmetrical waveform signal for each of said detected fixed reference points in cycle for cycle correspondence with the cycles of said input signal; and

((1) means for combining said detected peak value with the corresponding cycle of said symmetrical Waveform to provide a second symmetrical waveform in cycle-by-cycle synchronism with the first mentioned symmetrical waveform and having an amplitude corresponding with the peak value of the corresponding signal cycle.

10. In a system as set forth in claim 9, said symmetrical waveform signal generating means being a square waveform generating means, and said second symmetrical waveform being a square waveform.

11-.' In a system as set forth in claim 10, said detecting means comprising means for generating a pulse for a selected direction of zero crossing for each cycle of the fundamental frequency of said input signal.

12. In a system as set forth in claim 9, said detecting means comprising means for generating a pulse for a selected direction of zero crossing for each cycle of the fundamental frequency of said input signal.

13. In a system as set forth in claim 9, said unit further including means responsive to said detecting means for generating a blanking signal extending from shortly after a given detecting means pulse to shortly before the next succeeding detecting means pulse to blank out extraneous detecting means zero crossing pulses as may occur during a latter portion of a complex aural input tone.

14. In a system as set forth in claim 13, said symmetrical waveform signal generating means being a square waveform generating means, and said second symmetrical waveform being a square waveform.

15. A system for converting an aural input signal of one tonal character to an aural output signal of a different tonal character, including:

(a) a processing unit comprising means for detecting the fundamental frequency of said input signal;

(b) means responsive to said detecting means for generating a symmetrical waveform signal in cycle-forcycle correspondence with the cycles of said input signal;

() amplitude means responsive to the amplitude of said input signal to adjust the amplitude of said symmetrical waveform signal; and

((1) means for selectively varying the harmonic content of said symmetrical waveform signal.

16. A system according to claim 15, including means for converting the resultant signal to sound.

17. A system according to claim 15, including means for varying the amplitude envelope of a series of cycle of said symmetrical Waveform signal in accordance with a selected function.

18. In a system for converting an aural signal of one tonal character to an aural output of a different tonal character, means for determining the fundamental frequency of said signal, means for generating a symmetrical Waveform signal of said frequency, and means for varying the amplitude of each cycle of said symmetrical waveform signal in accordance with the peak value of the corresponding cycle of said aural signal.

19. In a system for converting an aural signal of one tonal character to an aural output of a different tonal character:

(a) means for determining the fundamental frequency of said signal;

(b) means for generating a symmetrical waveform signal of said frequency;

(c) means for varying the amplitude of each cycle of said symmetrical waveform signal in accordance with the peak value of the corresponding cycle of said aural signal;

(d) means for selectively varying the harmonic content of said symmetrical waveform signal; and

(e) means for converting the resultant signal to sound.

20. In a system as set forth in claim 19, means for varying the amplitude envelope of a series of cycles of said symmetrical waveform signal in accordance with a selected function.

21. In a system for converting an aural input signal of one tonal character to an aural output signal of a different tonal character, a processing unit comprising means for converting an aural input signal to a signal substantially rectangular in waveform and having a frequency equal to the fundamental frequency of said input signal, an amplitude control circuit including means for detecting the peak value of a given half of each cycle of said input signal, and means for combining said detected peak value with the corresponding cycle of said rectangular waveform signal to provide a resultant signal in cycle by cycle synchronism with the input signal and having an amplitude corresponding with the peak value of the corresponding input signal cycle.

22. In a system for converting an aural signal of one tonal character to an aural output of a different tonal character, means for determining the fundamental frequency of said signal, means for determining the peak amplitude value of each aural signal cycle, and means responsive to the first two means for producing a signal having a frequency equal to the fundamental frequency of the aural signal and each cycle having an amplitude related to said peak amplitude of the corresponding cycle of said aural signal.

23. A system for converting an aural input signal of one tonal character to an aural output signal of a different tonal character, a processing unit comprising means for detecting the fundamental frequency of said input signal, means responsive to said detecting means for generating a symmetrical waveform signal in cycle for cycle correspondence with the cycles of said input signal, and amplitude means responsive to the amplitude of said input signal to adjust the amplitude of said symmetrical waveform signal.

24. In a system for converting an aural input signal of one tonal character to an aural output signal of a different tonal character:

(a) a processing unit comprising means for converting an aural input signal to a signal substantially rectangular in waveform and having a frequency equal to the fundamental frequency of said input signal;

(b) an amplitude control circuit including means for detecting the peak value of a given half of each cycle of said input signal; and

(c) means for combining said detected peak value in synchronism with each cycle of said rectangular waveform signal to provide a resultant signal having an amplitude corresponding with the peak value of the corresponding input signal cycle.

25. A system for converting an aural input signal of one tonal character to an aural output signal of a different tonal character:

(a) a processing unit comprising means for detecting the fundamental frequency of said input signal;

(b) means responsive to said detecting means for generating a symmetrical waveform signal in cycle-forcycle correspondence with the cycles of said input signal;

(c) amplitude means responsive to the amplitude of said input signal to adjust the amplitude of said symmetrical waveform signal; and

(d) said processing unit further including means responsive to said detecting means for resetting said amplitude means extending for only a portion of a cycle of said symmetrical waveform signal.

26. A system for converting an aural input signal of one tonal character to an aural output signal of a different tonal character:

(a) a processing unit comprising means for detecting the fundamental frequency of said input signal;

(b) said detecting means comprising low pass filter means for said input signal to obtain the fundamental frequency thereof;

(c) means responsive to said detecting means for generating a symmetrical waveform signal in cycle-forcycle correspondence with the cycles of said input signal;

(d) said generating means comprising a first sawtooth waveform generator producing one cycle in response to each cycle of the fundamental frequency;

(e) amplitude means responsive to the amplitude of said input signal to adjust the amplitude of said symmetrical waveform signal; and

(f) a second sawtooth waveform generator responsive to the symmetrical waveform signal and producing one sawtooth waveform cycle in response to each symmetrical waveform cycle.

27. A system for converting an aural input signal of one tonal character to an aural output signal of a different tonal character:

(a) a processing unit comprising means for detecting the fundamental frequency of said input signal; (b) means responsive to said detecting means for generating a symmetrical waveform signal in cycle-forcycle correspondence with the cycles of said input signal; and

(c) amplitude means responsive to the amplitude of said input signal to adjust the amplitude of said symmetrical waveform signal, said amplitude means further comprising (1) means for detecting the peak value of a given half of each cycle of said input signal, and

(2) means for combining said detected peak value with the corresponding cycle of said symmetrical waveform to provide a second symmetrical waveform in cycle-by-cycle synchronism with the first mentioned symmetrical Waveform and having an amplitude corresponding with the peak value of the corresponding input signal cycle.

28. A system as set forth in claim 27, including a first output channel coupling said second symmetrical waveform to tone color filter means, a second output channel including means for converting said second symmetrical waveform to a corresponding sawtooth waveform and coupling it to tone color filter means, and means for converting the outputs of said tone color filter means to sound.

29. An amplitude control circuitcomprising means for detecting the peak value of a given half of an input signal, symmetrical waveform means responsive to said input signal to provide a first symmetrical waveform having a frequency octavely related to the fundamental frequency of said input signal, and means for combining said detected peak value with the corresponding cycle of said first symmetrical waveform to provide a second symmetrical waveform in cycle by cycle synchronism with said first symmetrical waveform and having amplitude corresponding with the peak value of the corresponding signal cycle.

30. A circuit as set forth in claim 29, wherein said first symmetrical waveform signal generating means being a square waveform generating means, and said second symmetrical waveform being a square waveform.

References Cited UNITED STATES PATENTS 3,094,666 6/1963 Smith 328- DONALD D. FORRER, Primary Examiner B. P. DAVIS, Assistant Examiner Us. 01. X.R. 84-124, 1.19; 307 235 Patent No.

Inventor(s) Dated November 4, 1969 D. J. Campbell It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 28, change "ampitude" to amplitude Col. 5, line 63, change "16" to 61 Col. 7, line 35, after "is" insert fed to a Col. 8, line 21, change "symmertical" to symmetrical Col. 9, line 63, change "cycle" to cycles SIGNED AND SEALED JUL? 1970 (SEAL) Attest:

Edward M. Fletcher, Jr. mun E i m. Amming 0mm Commissioner of Patents FORM PO-105O (10-69)

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3094666 *May 1, 1961Jun 18, 1963Lab For Electronics IncQuadrature axis-crossing counter
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3591699 *Mar 28, 1968Jul 6, 1971Royce L CutlerMusic voicing circuit deriving an input from a conventional musical instrument and providing voiced musical tones utilizing the fundamental tones from the conventional musical instrument
US3855893 *Sep 15, 1971Dec 24, 1974Chase Of CaliforniaElectronic organ employing multiple waveform tone generators and chiff generators
US4145943 *Jun 15, 1976Mar 27, 1979Norlin Music, Inc.Electronic musical instrument capable of generating a string chorus sound
US4168645 *May 20, 1977Sep 25, 1979Morris B. SquireElectronic musical instrument
US4280387 *Feb 26, 1979Jul 28, 1981Norlin Music, Inc.Frequency following circuit
US4300431 *Dec 14, 1979Nov 17, 1981Derocco PaulPitch extractor circuit
US4342246 *Jun 24, 1980Aug 3, 1982Cbs Inc.Multiple voice electric piano and method
Classifications
U.S. Classification84/681, 327/58
International ClassificationG10L21/00
Cooperative ClassificationH05K999/99, G10L21/00
European ClassificationG10L21/00
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Aug 29, 1985ASAssignment
Owner name: LOWREY INDUSTRIES, INC. 707 LAKE-COOK ROAD DEERFIE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:NORLIN INDUSTRIES, INC.;REEL/FRAME:004450/0317
Effective date: 19850402
Apr 10, 1985AS06Security interest
Owner name: FOOTHILL CAPITAL CORPORATION, 9911 WEST PICO BLVD.
Effective date: 19840928
Owner name: LOWREY INDUSTRIES,INC.
Apr 10, 1985ASAssignment
Owner name: FOOTHILL CAPITAL CORPORATION, A CORP. OF CA, CALIF
Free format text: SECURITY INTEREST;ASSIGNOR:LOWREY INDUSTRIES,INC.;REEL/FRAME:004390/0081
Effective date: 19840928