US 3591699 A
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Description (OCR text may contain errors)
United States Patent Royce L. Cutler 2625 Karbuch, Houston, Tex. 77018 716,964
Mar. 28, 1968 July 6, 1971 Inventor Appl. No. Filed Patented MUSIC VOICING CIRCUIT DERIVING AN INPUT FROM A CONVENTIONAL MUSICAL INSTRUMENT AND PROVIDING VOICED MUSICAL TONES UTILIZING THE FUNDAMENTAL TONES FROM THE CONVENTIONAL MUSICAL INSTRUMENT 20 Claims, 10 Drawing Figs.
US. Cl 84/1.11, 84/1.19, 84/1.22, 84/1.24 Int. Cl C1011 1/06, GlOh 1/00 Field oiSearch 84/1.01,
1.04, 1.06-1.17, 1.19-4.24, 1.26 B, 1.26 F, 1.26 FD, 1.26 G, 1.26U
Primary ExaminerMilton O. Hirshfield Assistant Examiner-Stanley J. Witkowski Attorney-Donald Gunn ABSTRACT: A voicing circuit for use with a conventional musical instrument. A tone pickup is placed on a conventional instrument. For example, a single coil is placed beneath each string on a guitar. The signal formed is the fundamental colored with many harmonics. An electronic circuit filters the harmonics to leave a much cleaner fundamental. The fundamental is voiced by a voicing circuit to add harmonics in such portions as to achieve a desired voicing. The voiced output follows the conventional instrument in terms of relative volume, shift in fundamental, vibrato of the fundamental.
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ATTORNEY MUSIC VOICING CIRCUIT DERIVING AN INPUT FROM A CONVENTIONAL MUSICAL INSTRUMENT AND PROVIDING VOICED MUSICAL TONES UTILIZING THE FUNDAMENTAL TONES FROM THE CONVENTIONAL MUSICAL INSTRUMENT RELATED APPLICATIONS Applicant has no presently pending related applications.
SUMMARY OF PROBLEM AND SOLUTION The present invention relates to electronic musical instruments cooperative withtone sources such as stringed instruments, horns and even human voices wherein the musical in-- strument forms a wide range of musical voices. Voicing to form selected musical effects and tones involves control of the harmonic content of a fundamental tone or note; the harmonies are mixed with varied amplitude and phase characteristics. On using an instrumental source, the source seldom, if ever, forms a pure fundamental as might be obtained from a tuning fork. Always, harmonics are mixed with the fundamental from the source. Further compounding the problem is the fact that apparently identical musical instruments vary in music quality and therefore in harmonic content resulting from their construction. The notes sounded on the same instrument will even vary in harmonic content when played slightly differently. For instance, a stringed instrument which is plucked at some point between the bridge and the nut is likely to vibrate in several different modes. If it is plucked perfectly vertically to the finger board, the mode of vibration is different from that when plucked horizontally. In all cases, the percentage of harmonics varies from note to note and even varies as a function of time because the harmonics die away at different rates. Even with an open string, plucking the stringat different angles and at different locations along its length will vary the harmonic mixture at all times after the note is sounded. With these factors in view, it will be appreciated that the phase angles, amplitudes, durations and time functions of harmonics vary in an unpredictable manner. This is true of all stringed instruments, whether plucked or bowed, and is likewise applicable to a great degree in all instrumental or tone sources including the human voice.
Since electronic voicing adds harmonics to a fundamental tone to derive a musical note of a desired quality, accurate foreknowledge of the harmonics derived from the tone source is very helpful. If the fundamental source is a clean sine wave (a tuning fork), this foreknowledge is accommodated by the voicing apparatus. However, clean tone sources are simply difficult to obtain from musical instruments. In the use of musical instruments, the requirements for a clean (sine) tone source are contradictory of the very nature of musical instruments since all musical instruments having any quality whatsoever incorporate a variable mix of harmonics.
In dealing with the problem of harmonic foreknowledge, attempts have been made in the prior art as might be noted by way of example hereinafter. For instance, the US. Pat. to White bearing No. 3,006,228, discloses a plurality of frequency dividers responsive to an input signal of mixed frequencies. The dividers from sine waves which are mixed by gates switched off and on. Further, the US. Patents to Cookerly, et al., bearing Nos. 3,325,579 and 3,213,180 illustrate modification of a conventional instrument to eliminate harmonics in the various tones. Likewise, a specially modified conventional stringed instrument is shown in the US. Pat. to Fender, et al., bearing No. 2,455,575.
In some devices of the prior art, no provision whatsoever is made for the variations in harmonic content so that the voicing of the input signal from the instrument does not control the musical quality of the output tone. By way of example, US. Pat. No. 3,213,180 discloses a circuit in which harmonics from the source mixed with the fundamental are merely fed through to the output. The patents indicate the failure of the prior art in providing a means for adapting a conventional and unmodified stringed instrument, horn, or the like for use as a tone source cooperative with voicing means. Because of the failure of the prior art, there is presently not available electronic musical instruments operated from a conventional tone source such as a stringed or wind instrument which provides suitable voicing to simulate a wide variety of musical instrument tones and the like. With this in view, the present invention is summarized as providing individual pickup means adapted to be positioned beneath single strings of an instrument for detecting the complex signal therefrom and providing a clean fundamental; said means further including voicing for 4, 8 and 16 foot pitches with flute or bright tones for instruments such as the flute, two string bass, bassoon, bass guitar, bass clarinet, soprano guitar, clarinet, oboe, horn, sitar, and the like.
One object of the present invention is to provide musical instrument apparatus voicing a tone from a conventional, unmodified instrument.
Another object of the present invention is to provide a new and improved means reducing harmonic content of a tone to yield an essentially clean fundamental.
A related object is to provide a new and improved circuit means voicing the sitar.
Yet another object of the present invention is to provide a means cooperative with a shortened string in which the fundamental varies perhaps two octaves and in which a clean tone essentially free of harmonics is formed.
A timely object of the present invention is to providetone pickup apparatus suitably installed on or removed from conventional string instruments.
An important object of the present invention is to provide time decay of the square wave tones to gain quality in tonal simulation.
Many other objects and advantages of the present invention will become readily apparent and an understanding thereof will be gained from a reading of the below included specification and consideration of drawings, wherein:
FIG. 1 shows a pickup means cooperative with a selected instrument, typically a guitar, as one tone source suitable for the present invention;
FIG. l-A is an enlarged detailed view of the pickup means of FIG. 1;
FIG. 1-15 is an enlarged detail view of the pickupmeans and its relationship to a string;
FIGS. vZ-A, 2-8, and 2-C are frequency response curves of portions of the circuitry;
FIG. 3 is a schematic wiring diagram of circuitry forming 4, 8 and 16 foot pitches;
FIGS. 4-A and 4-8 together illustrate voicing circuitry for use with the present invention; and,
FIG. 5 illustrates additional voicing means for the present invention.
In the drawings, attention is first directed to FIG. 1 which illustrates a guitar bearing the numeral 8. The device of the present invention will be discussed in cooperation with the guitar 8, although it will be appreciated that other stringed instruments, horns and selected tone sources are adapted for use with the present invention. The guitar 8 incorporates a finger board. 10 extending on the neck of the guitar to an adjustable means 11 for controlling the fundamental frequency of a string 12 adjacent the neck 10. The neck 10 has the frets l3 and a larger fret I5 which limits the length of the string 12. The string 12 passes over a bridge 14 at the upper end of the guitar 8. The string 12 is plucked near its center portions and vibrates from the lower fret 15 to the bridge 14. If fingered, the length of the vibrating string is determined by the particular fret 13 at which the instrument is fingered. Because the fingered string is shorter than the open string, the fundamentalhas a higher frequency.
In the conventional use of the guitar 8, or any other instrument for that matter, the string is plucked, bowed or otherwise vibrated along its free length ending at the bridge 14. The motion of vibration is definitely complex, always including a fundamental and perhaps eight or more harmonics of significant amplitude. The relative amplitudes of the harmonics vary depending on the point at which the string is plucked. For instance, if the string is plucked at its exact midpoint, this will tend to suppress or reduce the amplitude of the even numbered harmonics; however, they will not be diminished to zero.- Moreover, because it is impossible to fabricate a'totally rigid structure at the two end points of the string including the bridge 14 and the large fret 15, the vibrations coupled through the instrument to the bridge and large fret alter the harmonic amplitude and phase in a manner to sound notes which are a function of elapsed time in the vibrating string. While the foregoing is not to criticize anyinstrument and moreover describesthe varied characteristics that give each instrument its unique and often beautiful voicing,the above difficulties .are noted because the harmonics added in voicing must be controlled as taught by the present invention.
The numeral 16 indicates a pickup means attached to the musical instrument 8. The means 16 is enlarged in FIG. l-A which illustrates a mounting block 17 temporarily secured to the body of the guitar and which is adapted to support the various pickup coils as will be described. A single coil 18 is shown in FIG. LA and preferably incorporates a suitable bobbin having a number of turns wound thereabout wherein the signal is conducted to circuitry to be described by a pair of conductors 19. The coil 18 surrounds an inductor core 20 which is preferably magnetized and responsive to the string 12 positioned thereabove. In the preferred arrangement, the core 20 communicates magnetic flux variations to the coil 18 as the string 12 vibrates. When the string 12 is moved in near proximity to the core 20, the magnetic circuit is altered to varythe signal induced in the core 18. When the string moves back and forth above the upper face of the core 20, a suitable signal is induced in the coil 18. I
Since movement of the string 12 above the core 20 is governed by the fundamental and harmonics heard from the string 12, the string 12 induces the tones in the coil 18.
The core 20 is sensitive to the string 12. and not to the adjacent strings of the instrument 8. In the preferred embodiment, the distance between the core 20 and the string 12 is preferably about one-sixteenth inch, perhaps one thirtysecond of an inch. This does not interfere with the movement of the string since its range of movement at or near the bridge is not great enough to touch the core 20. With the spacing above-described, signals of magnitude are not detected from adjacent strings. A single pickup coil is adapted to be positioned beneath each string in the mounting means 17. shown in FlG. i-A to thereby provide specially tailored pickups for each and every string. Thus, if. the instrument includes six strings, preferably six pickups are individually placed across the span of strings with a magnetic core positioned immediately beneath each of the strings. A greater number of strings requires the use of additional pickups, again preferably one pickup per string. Y
While the foregoing describes installation of the pickup means with a stringed instrument, the present apparatus is adaptable for other types of pickups. For instance, a conventional microphone may be used in lieu of the magnetic induction coil means shown in FIG. l-A. Other known vibration pickups can be attached to horns, percussion instruments and the like, and conventional microphones can even be used with the human voice. Suffice it to say, the foregoing description is directed to the preferred embodiment of the stringed instrument pickup as will be described in detail hereinafter.
Attention is next directed to FIG. 3 of the drawings where the conductors from the magnetic pickup are indicated by the numeral 19. One side is grounded and the other conductor is communicated through a suitable coupling capacitor 24 to the base of the transistor 25. The transistor stage provides amplification wherein an output signal is developed across a collector resistor 26. The transistor incorporates a conventional emitter resistor 27 which is grounded and the base has suitable bias through a resistor 28. The amplified signal is applied to series resistors 29 and 30 and partially grounded through a capacitor 31. These circuit components, in cooperation with a capacitor 32, form a low-pass filter. The component values are selected so that the open string fundamental has a frequency signal to or somewhat higher than the break point in the filter curve at which higher frequencies are attenuated. That is to say, the fundamental frequency of the open string, the lowest frequency formed by the individual string 12, is made equal to. or slightly greater than the frequency at which the output of the filter begins to attenuate the harmonics. Attention is directed to FIG. 2-A which illustrates the filter characteristics as a function of frequency. v
The filter circuit described above is communicated with a transistor 34 which operates as an emitter follower with the output signal developed across the emitter resistor 35. The output signal is communicated through a series resistor 36 to a tank circuit comprised of capacitor 37 and an inductor 38. Preferably, the tank circuit is tuned to its optimum impedance at the fundamental frequency of the open string. Higher frequencies from the string are thusly attenuated quite rapidly with increase in frequency. The Q of the tank circuit need not be excessively high, but should be substantial to yield the characteristics shown in FIG. 2-8..
The transfer function of the tank circuit described above and the low-pass filter proceeding it should be considered. On plucking the open string 12, the fundamental frequency is the lowest possible tone derived from the string 12. The low-pass filter and the tank circuit together cooperate to slightly attenuate this fundamental. However, all harmonics of the open string are substantially attenuated so that the output signal from the tank circuit is an essentially clean sine wave.ln a typical'example, the second harmonic on the string 12 may have an amplitude equal to 50 percent or more of the fundamental. By using the circuitry described above, the second harmonic is substantially eliminated on reduction of the signal by several db. compared with the fundamental. FIG. 2-C shows the combined characteristics of the two circuits. Third, fourth and additional harmonics are even further reduced.
The effects on the fundamental and various harmonics of the filter and tank circuit for tones derived from a shortened string 12. When the string is shortened by fingering the frets 13, the fundamental of the shortened string is substantially higher in tone. On the composite response curve of the lowpass filter and the tank circuit in FIG. 2-C, the fundamental is ,thusly attenuated. However, the harmonics of the higher fundamental are substantially attenuated so that a relative reduction on the order of several dbfsis still obtained. Moreover, the absolute amplitude of the fundamental tone derived from the shortened string compares favorably with the amplitude of the fundamental of the open string, in spite of attenuation of the tank'circuit and the low-pass filter as shown in FIG. 2-3. The reason for this is the fact that the string 12 is brought ever closer to the magnetic coupling means 20 when the string is fingered. Since the coupling is a square law function, the smaller fundamental vibrations on the shortened string are still detected with sufficient amplitude by the pickup means and the attenuated output signal from the tank circuit is quite ample.
Resuming consideration of the amplifier circuitry in- FIG. 3, the tank circuit provides an input signal to the capacitor 40 for the base of the transistor 41. The transistor has a conventionalload resistor 42 and two emitter resistors 43 and 39. The connection of the resistor 39 is such to provide a volumn control.
An output resistor 44 communicates the amplified signal to additional circuitry as will be described, the signal being best described as the 8 foot pitch, a sine wave.
Reviewing the circuitry means mentioned hereinbefore, each of the strings of the instrument 8 forms a fundamental tone which is varied on fingering or shortening the string. As noted before, the fundamental is mixed with numerous harmonies; the circuitry described above substantially eliminates the harmonics to form the 8 foot pitch which is an essentially clean sine wave. The application of the sine wave to form other wave forms will be described hereinafter, and reference is made to the voicing circuitry as will be described also.
A coupling capacitor 45 communicates the 8 foot pitch to a transistor 46. The base voltage of the transistor is determined by a voltage divider including resistors 47 and 48. The transistor 46 is a phase splitter and for this reason, has equal value collector and emitter resistors 49 and 50. Coupling capacitors 51 and 52 communicate the opposite phase signals to a pair of rectifying diodes 53 and 54. The anode potentials of the diodes are determined by a resistive network including equal resistors 55 and 56. The resistors 55 and 56 are tied to a selected point on a voltage divider incorporating series resistors 57 and 58. The rectified positive pulses from the diodes 53 and 54 develop a wave form across a grounded resistor 59. The 4 foot pitch signal is output through a resistor 60.
' The phase splitter 46 forms out of phase signals at the 8 foot pitch. The diodes 53 and 54 pass only the positive half-cycles of wave form presented to each of the diodes which are then summed across the resistor 59. The summation provides the 4 foot pitch, at a frequency twice that of the 8 foot pitch. The
function and use of the 4 foot pitch will be thoroughly described hereinafter.
Attention is next directed to a resistor 64 which communicates the 8 foot pitch to a capacitor 65. The coupling capacitor 65 is tied to a grounded diode 66 which permits passage of only the positive half-wave pulses to the base of a transistor 67. The transistor 67 includes a conventional collector resistor 68 and suitable base bias is provided by a resistor 69. A coupling capacitor 70 derives an overdriven sine wave signal from the transistor 67, an almost squared waveform. The transistor 67 inverts the wave form which is then communicated to additional circuitry to complete squaring of the sinusoidal wave form. The signal is developed across a grounded resistor 71 and the signal is communicated through a diode 72 which is input to the base of a transistor 73. The base voltage is controlled by a resistor 74 tied to the 13+ supply line. The squared signal is developed across a collector load resistor 75. More will be noted concerning the use of the square wave from the above-described circuitry having a frequency to that of the 8 foot pitch.
A conductor 77 communicates a squared wave to a diode 78. More will be noted concerning the diode 78 hereinafter. Also, the conductor 77 is connected to a flip-flop 80. It is believed unnecessary to identify every circuit component of the flip-flop divider 80 since the circuit is well known in the art. It is significant to note that the signal on the conductor 77 is at the 8 foot pitch. The flip-flop 80 forms a square wave at half the frequency, or at the 16 foot pitch. The conductor 77 is input to the flip-flop 80 to actuate the flip-flop 80 with the 8 foot pitch. The output signal is derived on a conductor 81 which communicates with a diode 82 which will be described in conjunction with operation of the diode 78 hereinafter.
Attention is redirected to the 4 foot pitch formed at the phase splitter transistor 46. While one output is derived through the coupling resistor 60, an additional output is derived through a resistor 84 input to the base of a transistor 85. The transistor operation point is controlled by base voltage resistors 86 and 87. The degree of amplification of the transistor 85 is controlled by the variable emitter resistor 88 while the output signal is developed across a collector resistor 89. The polarity of the output signal should be noted. The rectifying diodes 53 and 54 form a positive input level to the base of the transistor 85. The signal is inverted by the transistor 85 High frequency components of the output signal are grounded by a capacitor 90 wherein the DC component of the amplified signal is input to a transistor 92 through a base resistor 93. Utilizing a PNP transistor to invert the wave form from the NPN transistor 85, the amplified signal from the transistor 92 is developed across the collector load resistor 94 and again high frequency components of the signal are grounded by a capacitor 95. The emitter of the transistor is connected to the supply line by a resistor 96. The output wave form is developed at the collector of the transistor 92. The
average of the tone derived from the musical instrument 8 fora sounded note, the amplitude builds quickly to a peak and decays for an interval of time. Likewise, the signal from the transistor 92 rises quickly to a peak value and decays during the same interval. This output signal is derived from the collector of the transistor and is used in the following manner.
The collector signal is communicated by way of resistors 96 and 97 to the anodes of the diodes 78 and 82 previously noted. The voltage wave form serves as a limiting envelope on the square waves passed by the diodes 78 and 82 to form a suitable wave form which decays in the proper manner. The diode 78 is connected to a resistor 98 to provide the needed output signal. Likewise, the diode 82 provides an output signal through a resistor 99 which is limited in envelope by the signal through the resistor 97. For convenience, the two signals are respectively called the 8 foot and 16 foot square waves.
Attention is next directed to FIGS. l-A and 4-8 of the drawings. In FIG. 4-B, the numeral 100 refers generally to the amplifier means of the present device which suitably matches the various voiced tones with an output amplifier of conventional construction for an output speaker. The function of the amplifier 100 will be noted in detail hereinafter after description of the voicing circuitry proper, the treble tone being generally synthesized by circuitry in FIG. 5 and the bass tones being provided by the circuitry in FIG. 4-A. The numeral indicates the voicing generally. First, the numeral 111 indicates a conductor from the treble tones while the numeral 112 indicates a conductor input from the bass tones. Should the device of the present invention be incorporated with a guitar having the standard six strings, musical nomenclature has identified the two larger strings as the bass strings while the remainder of the strings are grouped as the treble tones. Should the device of the present invention be used with something other than the guitar, one will note in many instruments a division of the keyboard or fingering such that bass and treble grouping of the tones is customary. For the guitar, and in accordance with the discussion hereinbefore, the circuit means 22 of FIG. 3 is duplicated for each string, and each tone pickup 16 previously described. Again, using the guitar only as an example, the four treble strings are communicated with a circuit means 22 and each of the four circuit means is output through the resistor 44 (see HO. 3) which provides the 8 foot pitch to the conductor 111. In like manner, the conductor 112 is connected to the various base tone circuits to derive the 8 foot pitch also.
Considering first the common circuitry, the numeral 113 indicates a conductor which provides a positive voltage to switching for turning off and on the various voicing circuits to be described. The numeral 114 indicates a conductor from a negative power supply and preferably, the negative and positive supply lines are equal levels relative to ground potential. The numeral 115 indicates the conductor on which the voiced signals are summed for input to the amplifier 100, the conductor 115 communicating with the circuitry of FIG. 5 which includes additional voicing circuitry. The conductor 117 communicates with a suitable voltage adjusted by a potentiometer to control the tone of the apparatus. As will be described, the tone control circuitry tends to ground certain high frequency signals to change the quality of the signal. The numeral 118 indicates conductor for the 16 foot bass square wave tones, those tones derived from the lower voiced portion of the stringed instrument, keyboard or other musical source. Also, the numeral 119 indicates the input conductor from the 16 foot treble square waves as will be used by the various voicing circuitry.
Considering the circuits illustrated, the conductor 111 is communicated through a resistor and input to a PET switch 126. A switch 127, preferably located convenient for the musician, communicates a positive voltage through a megohm resistor 128 to the gate of the FET 126. On operation of the switch 127, suitable bias voltage is applied to the gate to turn the transistor 126 on. In its conventional operation, it is biased off by a negative potential applied through a resistor 129 to the gate. To avoid erratic operation, high frequency signals at the gate are grounded through a capacitor 130. This leaves the voltage of the base essentially a DC level changed only on closure of the switch 127. When the switch is open, the gate is biased off and no signals are passed. When the switch 127 is closed, the source and drain are communicated together, thereby inputting the 8 foot pitch tone or signal to the conductor 115, the common bus for the amplifier 100.
The next voicing to be described is controlled by the switch 134. The switch means 134 provides voicing for the two string bass as will be described. The switch 134 provides a biasing signal through a resistor 135 to a FET switch 136. The FET is biased off by a resistor 137 connected to the negative voltage source 114. AC signals at the gate are grounded by a capacitor 138. The conductor 112 is input through a series resistor 139 while the 16 foot bass square waves are input through a resistor 140. The two inputs are summed with high frequencies grounded by a capacitor 141. The summed inputs are communicated through a resistor 142 to the FET switch 136. When the switch is biased on at the gate, the signals are communicated to the common bus 115 for the preamplifier means 100.
Attention is next directed to a switch 143 which provides voicing for the string bass. The switch 143 provides a gate voltage through a resistor 144 which is input to a FET 145. The FET 145 connects suitably filtered signals from the condoctors 112 and 118 to bus 115. In the quiescent condition, the FET is maintained off by the negative potential at the gate provided through a resistor 146. AC signals at the gate are again grounded by a capacitor 147. When the switch 143 is closed, the FET 145 conducts to communicate the voiced signals to the amplifier bus 115.
The next instrument to be considered is the bassoon, for which voicing is provided on closure of the switch 150.- The switch 150 applies a suitable bias through a resistor 151 to the gate of a FET switch 152. The FET switch is maintained in the off condition by the voltage applied to the gate through a resistor 153 which is connected to the negative supply line 114. Quality of the bias potential is maintained by the grounded capacitor 154. The bassoon signal is obtained from the l6 foot treble tones on the conductor 119. The bassoon voicing includes the following circuit elements. A double-tee filter including resistors 1540, 155, 156, 157 and 158 is input to the FET 152. One leg of the filter incorporates a grounded capacitor 159 which provides some forward phase shift. The other leg of the filter incorporates a grounded capacitor 160 which likewise provides forward phase shift. This leg further incorporates a grounded tank circuit including the inductor 161 and a capacitor 162. The characteristic sound of the bassoon Y is particularly aided by the resonant circuit which yields the pulsating sound characteristic of the woodwind.
The bass guitar is simulated on closure of a switch 166.'Closure of the switch 166 communicates on a level through a resistor 167 which is applied to a PET 168. In the normal condition, the FET is maintained off by a resistor 169 which is returned to a negative supply. Again, the gate is grounded by a capacitor 170 to remove AC signals from the gate. The bass guitar is obtained from the 16 foot tones on the conductor 119. Suitable high frequency grounding is provided by the circuitry which incorporates series resistors 171, 172, and 173, and high frequency grounding capacitors 174 and 175.
The numeral 177 indicates the switch which provides voicing for the bass clarinet. The switch 177 operates through a resistor 178 to switch off and on a FET switch 179. The FET 179 is normally maintained off by a resistor 180 connected to the negative supply line 114. AC signals at the base are grounded by a capacitor 181. The input to the FET 179 is from the conductor 119 again. The conductor 119 is input to series resistors 182 and 183. Some AC grounding is provided by a capacitor 184. The grounding is not as substantial as that provided by the capacitors 174 and 175 in the bass guitar, it being appreciated that the bass clarinet includes a richer portion of high frequency tones.
The above tones are input to the conductor115 for the preamplifier means 100. The conductor 117 for the tone control means responds to a suitable voltage at a control convenient'for the musician and is input through the base of a transistor 188. The base incorporates a series resistor 187. The transistor 188 is used as a switch to vary the quantity of the capacitor 189 connected between the signal conductor 115 and ground. AC signals at the base of the transistor 188 are grounded by a capacitor 190. When the transistor is switched off, the capacitor 189 provides no conduction to ground. However, when the transistor I88 conducts, it serves as a switch in a varying degree controlled by the base signal whereby the capacitor 189 is partially or even completely grounded. As this is controlled, the quantity or measure of high frequency signals grounded by the transistor circuitry is also varied.
Continuing on with FIG. 4b tocomplete the amplifier means 100, attention is next directed to the input capacitor 200 of the amplifier means 100. An emitter follower transistor 201 hasa suitable bias from a voltage divider including resistors 202 and 203. The output signal is developed across an emitter resistor 204. The output signals are coupled through a blocking capacitor 205 to additional circuitry. The next stage of the amplifier incorporates an amplifying transistor 206. Base voltage is determined by a resistor 207 returned to the collector, and the transistor includes conventional collector resistor 208 and emitter resistor 209. The output signal is developed across the collector load resistor 208 and emitter resistor 209. The output signal is developed across the collector load resistor 208 and is coupled by a capacitor 210 to additional circuitry.
Volume control of the preamplifier means is provided at a conventional rheostat convenient to the musician. Viewing the circuitry again, the resistors 211 and 212 provide slight grounding of the signal in parallel with a resistor 213. The resistor 213 is'grounded under control of a transistor 214. The transistor 214 obtains its base voltage through a series resistor 215 which is communicated with a variable voltage source on a conductor 216 communicating from the volume control of the musician. As the musician selects a suitable base voltage for the transistor 214, the degree that the transistor is turned off or on varies the resistance in the circuit. AC hum is prevented by a capacitor 217 which is grounded at the base of the transistor 214.
A coupling capacitor 220 transfers the signal after the volume has been adjusted, and further amplification is obtained from a transistor amplifier 222. The amplifier 222 incorporates a base to collector resistor 221 in the megohm range. The transistor has a conventional collector resistor 223 and grounded emitter resistor 224. The output signals are developed across the collector load resistor 223. A coupling capacitor 225 provides an audio output signal on a conductor 226. To prevent charge accumulation on the capacitor 225, a substantially large resistor 227 is grounded on the output side at the conductor 226.
While the foregoing describes the preamplifier means 100 from which the voiced signals (musical tones) are relayed to a suitable amplifier and speaker system, the conductor shown in FIG. 4A is also found in FIG. 5 in communication with additional voicing means. For this purpose, attention is next directed to FIG. 5 for a description of the additional voicing. The voicing provided in FIG. 5 is denoted as the treble voicing generally, although no particular classification is intended by this description.
Attention is directed to the input conductors 111, 112, 118 and 119 in FIG. 4A. In addition, the bass and treble division for other tones is likewise effected in FIG. 5. The numerals 230 and 23] indicate the bass and treble tones, respectively, of the 8 foot square wave. Likewise, the numerals 232 and 233 indicate the bass and treble, respectively, 4 foot pitches input to the circuitry from the various tone generator means 22 described hereinbefore. Again, it should be emphasized that the bass and treble designations used herein imply a split keyboard, or other split voicing as in the guitar 8. With other fier 240. The conductor 232, on which the bass tones are I derived, is input to the drain of the same transistor. The transistor 240 is biased off in the normal condition by connection of a resistor 241 to the negative supply 114. Additionally, a resistor 242 communicates with a switch 243 connected with a positive supply 113 for turning on the FET 240. In the quiescent condition, the FET is biased substantially off until closure of the switch 243. When the switch is closed, the channel conducts to communicate the source and drain. The source and drain are also connected by way of resistors 244 and 245 to ground.
Similar circuitry is provided for the conductors 111 and 112 on which the treble and bass 8 foot tones are derived. Attention is directed to the FET 246 which likewise incorporates the resistors 247 and 248 connected to ground. The F ET has a common base connection with the FET 240 and utilizes the switch 243 in the same manner.
The conductors 230 and 231 are both input to the FET 250. Again, the source and drain are communicated to ground by way of resistors 251 and 252. The gate of the F ET 250 is common to the gates of the previously noted transistors and obtains switching voltage in the same manner. Lastly, the conductors 118 and 119 are input to a FET 254 associated with the resistors 255 and 256. The FET 254 functions in the same manner as those described heretofore, its gate being common to resistors 241 and 242 which provide the control voltages. A capacitor 257 grounds high frequency signals picked up at the gates of the various transistors to prevent modulation of the switching transistors.
Concerning the voicing illustrated in FIG. 5, attention is first directed to a FET 264 which serves as a switch to the voicing of the guitar. A switch 265 connected with a resistor 266 turns on the FET 264. The FET 264 is normally turned off by connection of a resistor 267 to a negative supply. Again, AC signals at the base are grounded by a capacitor 268. The FET 264 sums two inputs, one of which is derived through a resistor 269 directly to the summed treble and bass 8 foot pitch tones. The other input is the 4 foot pitch tones input through the resistor 270, grounded capacitor 272, and additional resistor 271 which provides some phase shift to the signal. The transistor 264 is connected to the conductor 115 which is the signal bus input to the preamplifier means 100 shown previously in FIG. 4B.
Voicing for a soprano guitar is actuated on closure of a switch 275. The switch provides control voltage through a resistor 276 to a FET 277. Normally, the FET 277 is turned off by connection of a resistor 278 to negative supply while again, AC signals at the gate are grounded by a capacitor 279. The single input to the soprano guitar voicing circuitry is the 4 foot pitch tones. The input is derived through series resistors 281 and 282 with a grounded capacitor 283 providing some roll off with higher frequencies.
Voicing for a clarinet is provided on actuation of a switch 285. A sufficient voltage for turning on a FET transistor 287 is conveyed through the resistor 286 to the gate. The gate incorporates connections through a resistor 288 to a bias source while AC signals at the gate are grounded by a capacitor 289.
Voicing for the clarinet utilized the 8 foot square wave tones. The signals are input through series resistors 290 and 291 with some of the high frequency content of the square waves grounded by a capacitor 292.
Voicing for the oboe is initiated on closure of a switch 295. The switch 295 turns on a FET transistor 296 on application of voltage through a resistor 297 to the gate. The gate is normally turned off by a resistor 298 connected with a negative supply while AC signals are grounded by a capacitor 299.
The oboe voicing is derived from the 8 foot square wave, both bass and treble. The transistor 296 is provided with a summed input wherein the square wave is communicated through serialresistors 300 and 301. The resistive circuitry inputs the square wave to a resonant circuit including a capacitor 302 and inductor 303. The square wave input causes the resonant circuit to ringwhich adds the rasping high frequency tones to the square wave input to the FET 296. The extent of the ringing square wave is reduced by series resistors 304 and 305 and grounded capacitor 306 which reduce the ringing amplitude and modify the slope of the square wave input to the transistor 296. It will be appreciated from the foregoing that the oboe voicing is derived from the circuitry described.
A switch 310 provides horn voicing whereupon closure biases a PET 312 through a resistor 311. The FET 312 is maintained off by a resistor 313 connected to a negative supply and high frequency signals at the gate are grounded by a capacitor 314. Again, the square wave input is utilized for the voicing of the horn. The signal is input through the series resistors 315 and 316. Again, a resonant circuit including a capacitor 319 and an inductor 318 is connected by way of a resistor 317 to the resistor 316. The ringing of the resonant circuit adds the quality of the horn to the square wave.
A switch 325 controls voicing for the sitar. The switch provides a voltage through a resistor 326 which counteracts the bias resistor 327. The resistors and a capacitor 328 are connected to the gate of a FET 329. The FET has one input from a resistor 330 connected by a conductor 331 to the conventional guitar pickup on the instrument. These devices are well known in the art. A series of resistors 322 and 333 input a square wave to a resonant tank including a capacitor 334 and an inductor 335. The ringing of the oboe tone imposed on the electric guitar sound so well known simulates the sitar in a very realistic manner.
As before stated, all the voiced signals are supplied to the amplifier means in FIG. 4b. The output is then conducted to the conventional amplifier and speaker for audio reproduction. Particular emphasis is placed on control of the harmonic content. The voicing circuits described herein add consistent harmonic content to the fundamental, and the problem of an unmeasured and variable quantity of harmonics in the input is avoided by the present invention. Moreover, the close control of harmonic content is achieved even with conventional tone sources, without modification by a pickup means which is both easily attached and removed. Thus, the deficiencies of the prior art are cured in that the voicing is perfectly controlled in the circuitry and is not irregularly poor because of change in .the tone source harmonics.
Many alterations of this invention are available to one skilled in the art. Rather than enumerate them, the scope of the present disclosure is determined by the claims appended hereto.
1. Electronic musical apparatus for forming musical notes voiced in a predetermined manner and adapted to be used with a typical stringed instrument having strings which are selectively shortened to alter the tone of the instrument, the tone formed by the instrument including a fundamental and harmonics and which comprises:
a. first transducer means for forming a signal proportional to an individual strings vibrations, said means being adapted to be operably coupled with one string on a typical musical instrument which forms notes having a fundamental and mix of harmonics of various phases and am plitudes;
b. second transducer means for forming a signal proportional to a second individual strings vibrations, said means being adapted to be operably coupled with a second string of such instrument;
c. positioning means for positioning said first and second transducer means operably coupled with first and second individual strings, said means positioning said transducer 'means at selected distances from the individual strings and a closer distance from the strings when the strings are shortened to cause said transducer means to form a larger signal for notes made on respectively shortened strings;
d. first filter means connected to said first transducer means;
e. second filter means connected to said second transducer means; I
f. each of said filter means being individually tuned for attenuating the various hannonics, their respective signals relative to the fundamental, and each having a rolloff point approximately equal to or greater than the fundamental frequency of the respective open strings, and further having a rolloff which relatively attenuates the harmonics of the notes of shortened strings in comparison with the fundamental of notes of the shortened strings, said filter means forming respective output signals of the relatively filtered fundamentals of the open and shortened. strings; and,
g. voicing means including first and second voicing circuit means for voicing the fundamentals from said first and second filter means for selectively forming first and second voiced musical notes.
2. The invention of claim 1 wherein said last-named circuit means forms a signal having twice the frequency of the fundamental.
3. The invention of claim 1 wherein said last-named circuit means forms a signal having half the frequency of the fundamental.
4. The invention of claim I wherein said voicing means means means means me ans means forms a signal having the quality of the two string bass.
10. The invention of claim 1 wherein said voicing means forms a signal having the quality of the guitar.
11. The invention of claim 1 wherein said voicing means forms a signal having the quality of the soprano guitar.
[2. The invention of claim 1 wherein said voicing forms a signal having the quality of the clarinet.
13. The invention of claim I wherein said voicing means forms a signal having the quality of the oboe.
14. The invention of claim 1 wherein said voicing forms a signal having the quality of the horn.
15. The invention of claim 1 wherein said voicing forms a signal having the quality of the sitar.
16. The invention of claim 1 wherein said last-named circuit means forms a square wave signal.
17. The invention of claim 16 wherein the frequency of the square wave signal is equal to that of the fundamental from the musical instrument.
18. The invention of claim 16 wherein the frequency of the square wave signal is equal to half that of the fundamental from the musical instrument.
19. The invention of claim 16 including an additional circuit means for limiting the envelope of the square wave signal in a manner to decay the signal.
20. The invention of claim 19 wherein said additional circuit means is responsive to the time decay of the musical note sounded on the musical instrument.
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