US 3801721 A
Description (OCR text may contain errors)
United States Patent [1 1 Bunger Apr. 2, 1974 MONOPIIONIC ELECTRONIC MUSIC SYSTEM WITH APPARATUS FOR SPECIAL EFFECT TONE SIMULATION [7 5] Inventor: David A. Bunger, Cincinnati, Ohio  Assignee: D. II. Baldwin Company, Cincinnati,
 Filed: June 16, I972  Appl. No.: 263,649
Related 0.8. Application Data  Continuation-impart of Ser. No. 213,939, Dec. 30,
 0.8. CI 84/1.19, 84/l.24, 84/].25, 84/DIG. 2, 84/DIG. 20  Int. Cl. G10h 1/02, GlOh 5/10  Field of Search 84/1.01, 1.03, 1.11-1.13, 84/1.17, 1.19-1.26, DIG. 4, DIG. 9, DIG. 2, DIG. 20
 References Cited UNITED STATES PATENTS 2,403,664 7/1946 Langer 84/l.21 2,710,555 6/1955 Martin 84/1.0l 3,260,784 7/1966 Wehrmann 84/l.01 3,283,057 11/1966 Campbell 84/1.0l 3,288,904 11/1966 George 84/1.01 3,288,907 11/1966 George 84/].25 3,490,327 l/l970 Volpe 84/].25 3,609,203 9/1971 Adachi.... 84/l.01 3,665,089 5/1972 Stearns 84/].01 3,715,445 2/1973 Kniepkamp 84/1.l3 3,733,955 5/1973 Reinagel et al.... 84/l.01 2,933,004 4/1960 l-Ianert 84/1.0l 3,051,032 8/1962 Hanert.... 84/1.l9 3,509,262 4/1970 Munch.... 84/].01 3,538,804 11/1970 George 84/l.0l
OTHER PUBLICATIONS I-I. F. Olson, Electronic Music Synthesis For Recordings, IEEE Spectrum, April 1971, Vol. 8, No. 4, pp. 18-30.
Primary ExaminerRichard B. Wilkinson Assistant Examiner-Stanley J. Witkowski Attorney, Agent, or Firm-Hyman Hurvitz  ABSTRACT of the order in which the keys are struck. If several keys are released at approximately the same time, only the tones derived in response to the highest remaining activated key are voiced, regardless of the release sequence. In response to the system being played legatissimo, voiced tones gradually shift in frequency, i.e., portamento is achieved. In response to the system being played staccatissimo, voiced tones shift in frequency in discrete steps. For unusual or special effect tone simulation, square wave tone signals derived from a frequency divider chain responsive to a voltage controlled oscillator, controlled primarily by the nomenclature of the highest pitch struck key, may be converted into a sawtooth waveform, a pulse waveform having a pulse width controlled by the highest pitch struck key, or can be left unaltered. Clicks and noise can be derived in response to key activations. The sawtooth, pulse, square wave, clicks and noise are fed through a filter selectively having band pass, low pass and high pass transfer characteristics that can be controlled with regard to resonant frequency and selectivity (Q) to provide additional unusual effects. A first group of tone signals derived from the frequency divider is processed to simulate flutes while a second group is processed to simulate brasses. In flute simulation, filtering of harmonics and passage to an output of the fundamental of the tone associated with the highest pitch struck key is assured by including in cascade a low pass filter and an amplifier having a variable gain characteristic directly related to the nomenclature of the highest pitch struck key. In brass simulation, an attack envelope having plural slopes is provided. Brass brightness is controlled by providing a variable wave shaper that responds to pedal control or is a transient function during the attack of the voice. Flatting during the attack of a brass tone is simulated by transiently reducing the voltage controlled oscillator frequency when a new highest pitch key is struck by an amount indicative of the nomenclature of the struck key. Attack rates of the flutes and unusual tones can be controlled to a plurality of values; if the system is in a percussive mode the attack rate is relatively fast. Roll-off rate of certain flute tones is fixed, while other flute tones and the unusual tones can be provided with a fixed roll-off or sustain effect. The voltage controlled oscillator frequency is modulated by a vibrato through frequency is modulated by a oscillator, the frequency of which can be fixed or controlled in a random manner in response to a noise source to simulate brass vibrato effects.
24 Claims, 14 Drawing Figures LEGEND PATENTEDAPR ZISM SHEEI 8 0f 9 i/QGI 1 262 1 263 148 FROM PATENIEBm 2 m4 SHEEISUFQ mom gum.
. v6? mww 5 RELATIONSHIP TO COPENDING APPLICATION The present application is a continuation-in-part of my copending US. Pat. application filed Dec. 30, 1971, Ser. No. 213,939.
BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION As an accompaniment to conventional electronic organs, tone synthesizers responsive to a signal indicative of a nomenclature (i.e. note) associated with a highest pitch struck key on an organ keyboard have been developed. Synthesized tones are derived that are chordally and octavally related to the tone of the highest pitch struck key. Most prior art synthesizers require the musician always to depress the highest pitch key of a note grouping or chord first and release thehighest pitch key; last. lfthis technique, which many musicians find difficult to perform, is not followed, the melody effect is voiced on the note which is first depressed and jumps to the second depressed note, until the highest note of the chord has been struck. The resulting continuous jumping from note to note until the highest note of the chord is struck occurs because of the musicians inability, no matter how skilled, to depress consistently all of the keys of a chord at precisely the same time or to cause the highest pitch key of the chord to be depressed first. A' similar effect occurs in reverse in response to the musician attempting, but failing, to re lease all of the keys simultaneously.
Systems which partially remove the keying accuracy requirement of the musician are disclosed in US. Pat. Nos. 3,288,904 and 3,538,804. The patented systems employ a high note guard arrangement to prevent a change infrequency of voiced sounds in the event the highest pitch struck key of a played chord is released by the musician until a new chord or highest pitch struck key of-a played chord is released by the musician until a new chord or highest pitch struck key is subsequently played. The prior arrangement prevents tones associated with the highest pitch struck key from decreasing in frequency in response to release of the high-' est pitch struck key, a desirable feature only when the musician intends to'release all of the keys approximately simultaneously. If the musician modifies the played chord to form anew chord wherein the highest depressed key is of lower tone than the previously highest depressed key, to provide a melody effect, the high 'note guard requires the musician to release and then depress the key which has now become the highest pitch key of the new chord. Otherwise, the melody effect of the synthesizer does not enhance the tones accompanying the new, lower pitch, highest pitch struck key. Hence, the prior art system requires the musician to develop a specific, unnatural technique for shifting from one key combination to another. Further, if the musician has released all of the depressed keys and then attempts to play another key combination, the high note guard circuit of the prior art does not eliminate the requirement for the musician to depress the highest tone key of the chord before striking any of the other keys.
which includes keys of the first key grouping, within 60 milliseconds. Advantage is taken of this discovery by delaying voicing of any tones associated with a new key grouping for a predetermined time period, 20 milliseconds or less. In shifting from one key grouping to a second key grouping, which includes keys of the first key grouping, coupling of tones associated with the highest struck key of the second key grouping are not voiced until approximately 60 milliseconds has elapsed from the first release of a key of the first key grouping. By delaying voicing of tones associated with the highest struck key of a grouping, the musician is not required to strike and release the keys in an unnatural manner and voicing of tones associated with keys other than the highest pitch key of a key grouping is precluded.
portamento is provided in response to the musician striking the keys legatissimo. Thereby, in response to a subsequent key grouping being struck while another previously struck key grouping is being voiced, wherein the subsequent key grouping has a higher pitch key than the previous key grouping, tonesare smoothly shifted from frequencies associated with the highest pitch key of the previous grouping to the highest pitch key of "the subsequent grouping. If the keys are activated staccatissimo, the change in frequency from one key grouping to another key grouping is in discrete steps. v
In accordance with a further feature of the invention, unusual or special tones are synthesized in response to ton'esjderived in response to the highest pitch struck key of a key grouping or in response to each change in the highest pitch struck key or noise. In response to the derived tones, tonesignals having different harmonic content, represented as square waves, triangular waves and pulses are derived. The pulse widths are controlled by the highest pitch struck key within a grouping. These synthesized tones provide organs of the present invention with a wide variety of sounds and effects heretofore not previouslypresented on commercially attack tone color change, tone color change as a function of the dynamic level of the voiced tone, and overall tone quality. It has been found that attack rate is typically composed of a pair of exponentially related, sequentially derived envelopes as the tone is being initially voiced. The efiect is achieved with the present instrument by amplitude modulating tones derived in re-v sponse to the highest note voices being initially sounded. It has also been found that brass tones, when initially voiced, have a tendency to be transiently flat.
The flatting effect is simulated with the present invention by reducing, on a transient basis, the frequency of tones derivedin response to initial striking of the highest pitch key. The amount of frequency reduction is dependent upon the highest note depressed to provide ac- 'curate simulation of initial brass voicing. It has also the voice as time progresses, for the simulated brass tones. Also brass tone color brightness is increased as dynamic level increases, an effect attained by increasing the harmonic content of the voice with another wave shaping circuit as tone level increases.
According to a further feature of the invention, there is provided a new and improved network for simulating the characteristics of flutes. Previously, it was the general practice to simulate flutes with fixed filters or complex, expensive filters having cutoff frequencies varied in responsetothe input frequency thereof. In accordance withthis feature of the invention, a simple, inexpensive flute filter is providedfor passing the fundamental of the highest pitch key, and for rejecting harmonics, regardless of the fundamental frequency of the highest pitch struck key and of the harmonicsthereof. Such result is attained by cascading a fixed, low pass filter with a variable gain amplifier, the gain of which is controlled as a direct and linear function of the nomenclature of the highest pitch struck key. Control of the gain of the amplifier is achieved in a relatively simple manner since the frequency of generated tones is controlled in response to a voltage linearly related to 'the highest pitch struck key, said voltage is supplied as a gain control'to the amplifier.
ln accordance'with another feature of the invention, theattack rate of flute tones and the unusual tones may be controlled, upon the will of the musician, depending upon a selected operating mode. In a so called continu- -ous mode,'the attack rate for the flutes and unusual tones can be either relatively fast or slow. In a percussive mode, wherein tones are derived for only a predetermined time after activation of a key grouping, regardless of whether the key grouping remains struck, the attack rate is always relatively fast. In both modes, the roll-off rate of certain of the flute tones, subsequent to release of the keys, is fixed. For other flute tones and the special tones, a sustain effect is provided with the organ inthe percussive mode and'can be provided, at the will of the musician, in the continuous mode."
A common aspect of many of the features is control of tone frequency and content in response to a voltage indicative of the nomenclature of the highest pitch struckkey. The voltage, in addition to controlling the tone frequency of a voltage controlled oscillator (as in my copending application), provides tone content control ina simple and inexpensive manner with regard to: flatting extent, tone pulse width, flute filter amplifier gain, and, in certain instances, resonant frequency of a voltage controlled filter selectively having low pass, high pass and band pass characteristics responsive to the unusual tone sources.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram of a preferred embodiment of the invention;
FIG. 2 is a circuit diagram of a keyswitch circuitry, a note played detector circuit, and sample and hold circuit included in FIG. 1;
FIG. 3 is a circuit diagram of mode selector circuitry included in FIG. 1; I I
FIG. 4 is a circuit diagram of a wave form shaper included in FIG. I;
FIG. 5 is a circuit diagram of a voltage controlled oscillator and related circuits of FIG. I;
FIG. 6 is a partial block, partial circuit diagram of brass filters used in FIG. 1;
FIG. 7 illustrates a waveform derived in FIG. 6;
FIG. 8 is a partial block, partial circuit diagram of the flute filters used in FIG. 1',
FIG. 9 is a modification of one filter of FIG. 8;
FIG. 10 is a circuit diagram of avoltage controlled filter used in FIG. 1;
FIG. 11 is a circuit diagram of a vibrato oscillator, noise source and associated circuitry used in FIG. I; and
FIGS. 12 and 13 are waveforms to the oscillator of FIG. 11.
DETAILED DESCRIFIIONIOF THE DRAWING Block Diagram, FIG. 1
Reference is made to FIG. 1, wherein an electronic organ is illustrated as including a plurality of tone generators 1, each of which may be composed of plural independent oscillators, one for each note of the organ, or may involve frequency dividers. In the latter case there are traditionally twelve master oscillators for each generator, covering the uppermost octave 'of notes, from which lower octave tone signals of a manual are derived by frequency'division. In the alternative and'in accordance with the more recent practice, there is a single master oscillator from which all notes of a manualare derived by rate scaling. In any event, the
assist in describing outputs of the tone generators are conventionally se-' outputsof the voicing circuits 4 are applied to'the' input of a pre-amplifier 17, which in turn drives a power amplifier 5, and a loudspeaker 6, or other acoustic radiat-' ing system. The gain of the -pre-amplifier 1 7 is controlled by an expression pedal 1880 that tone amplitude is increased as the pedal is depressed. This much is conventional and is. contained in many presently commercial electronic organs.
The present invention includes a tone synthesizer that is activated simultaneously, in superposition, with the conventional organ in response to depression of the same keys on keyboard 2 as the keys that control gating of generators 1. The output of the synthesizer is controlled in several operating modes. The various operating modes are selected by means of mode se'lectorl9. Available modes arei (l) reiteration; (2) percussion; (3) normal (or continuous); (4) fast attack; (5) slow attack; and (6) sustain.
Control of the synthesizer tones is in response to activation of keyboard 2 that selects a voltage from voltage divider 3and applies this voltage to lead 24. The voltage represents, in terms of its magnitude, only the nomenclature of the highest pitch key played on keyboard 2, as disclosed in my copending US. Pat. application, Ser. No. 213,939, filed Dec. 30, 1971. The voltage on lead 24 is supplied to sample and hold circuit 8 which provides on its output lead a voltage equal to the voltage on lead 24. The voltage at the output of circuit 8 is derived for a time which endures after all played keys are released, or until a different key combination is struck. The sample and hold circuit 8 is activated in response to control signals provided by a note played detector 7 connected to lead 24 to respond to any change of the highest pitch actuated key. The output frequency of a voltage controlled oscillator (V.C.O.) 9 is established primarily by the control voltage supplied to it by the sample and hold circuit 8.
The V.C.O. 9 provides at its output 100, a square wave signal, the fundamental frequency of which corresponds with the highest note called for by the actuated keys of keyboard 2. The output of V.C.O. 9 is applied to a frequency divider chain 10, which has several outputs for providingan array of square wave tone signals 'chordally and octavely' related to the signal provided by responsive to the 32' and 16' outputs of chain 10; filters 12 for flute simulation are responsive to the 16, 8', 4,, 2 4% and 1 Va outputs of chain 10; and wave shaper 22, for unusual tone simulations, responds to the 32', 16' and 8' outputs. Filters 11 and12 and wave shaper 22 include an input circuit for each of the footages supplied to it. Filters 12 are arranged so that the 16', 8, 4' tones are combined on a first output lead 12a and the 2 34s and 1 A1 tones are combined on a second output lead 12b.
Wave shaper 22 is also responsive to signals from noise generator 21 and to key activation pulses from note-played detector 7. In addition, the square wave tone signals derived from divider chain 10 are selectively processed, at the will of the musician, in wave shaper 22 as shortened pulses or, sawtooth waveforms or they may be substantially unmodified. The widths of the pulses are controlled in response to the output of sample and hold circuit 8 so that low note key depressions result in wider pulses than high note key depressions. Wave shaper 22 includes operator activated controls for selecting these various waveforms.
Brightness effects of the brass instruments simulated by filters 11 are achieved with variable waveshaping circuits controlled by depression of expression pedal 18, and for simulation of certain instruments, as a function of time elapse after a key has been played. in the latter case, as time progresses there is less attenuation of harmonic tones, whereby greaterbrightness is provided as time progresses after initial key activation. In response to depression of shoe 18, the harmonic content of the tone is increased by another waveshaping circuit so as to provide greater brightness as dynamic level increases. Filters 11 also include means for simu lating brass attack characteristics by amplitude modulating the tone signals fed thereto with an envelope that includes plural exponential characteristics.
Filters 12 consist of a series combination of a voltage controlled amplifier and a fixed low pass filter. The gain characteristic of the voltage controlled amplifier is proportional to'the output voltage of sample and hold circuit 8. Thus the gain of the voltage controlled amplifier is proportional to the fundamental frequency of the input. This causes the output of the fixed low pass filter to remain constant with-regard-to fundamental frequency over a given input frequency range while attenuating the harmonics of the fundamental frequency inputat a fixed db per octave rate.
Filter 11 and wave shaper 22, as well as linear gates 14 and 15 (which may take a form disclosed in U. S. Pat. No. 3,549,779) are responsive to control signals derived from note played detector 7, as coupled through mode selector 13, a predetermined time, e.g., 20 milliseconds, after the first note of a key combination has been played. The control signals enable the tone signals to be passed through filter 11 and wave regardless of which key was actually struck first. lf the musicianselects a continuous, rather than percussive, mode, tonal signals may be derived from gates 14 and 15 and wave shaper 22 as long as a key is depressed or, at the will of the musician, a sustain effect after key releasecan be provided for tones derived from gate 14 and wave shaper 22. On the other hand, if the percussive mode is selected, control signals supplied by mode selector 19 to gates l4, l5 and wave shaper 22, enable the wave shaper and gate 14 to provide a controllable sustain, while gate 15 provides a fixed, short sustain.
In response to one or more keys being released while one or more other keys remain depressed, the tone signals derived from filter 11 and wave shaper 22, as well as from gates 14 and 15 are shifted to tones corresponding with the highest pitch of the remaining depressedkeys. In response to all of the keys being re- I leased, the control signals from mode selector 19 are removed from filter 1!, wave shaper 22, as well as gates 14, 15. Circuitry in sample and hold circuit and note played detector 7 delay the V.C.O. 9 from shifting frequency for a predetermined time, e.g., 40 milliseconds, after release of a key so that if several keys are substantially simultaneously released, tones associated with only the key having the highest pitch are derived, regardless of which key was actually the last to be released. lf there is activation of a new key of higher pitch than any other depressed key, tones associated with the new key are derived from filters ll, wave shaper 22 and gates 14, 15 20 milliseconds after striking the new key even though another key was just previously released.
A random, vibrato tonal effect, on the signal derived from V.C.O. 9 is selectively derived from low frequency modulation oscillator 20 via lead '20a, the center frequency of which can be operator controlled.
-Random vibrato is particularly effective in simulating 7 domly varies the output frequency of modulator 20 about its center value. The amount of random variation is controllable, with typical maximum deviations of i percent about the selected center vibrato frequency.
In the reiterative mode, the output frequency of oscillator is fixed, with no random variations imposed.
In response to note played detector deriving a signal to indicate that any note is being depressed, oscillator 20 modulates V.C.O. 9 at a fixed frequency. In synchronism with the fixed frequency modulation supplied by oscillator 20 to V.C.O. 9,'reiteration pulses are suppliedby oscillator 20 to mode selector 19 which, in turn, under the control of the musician, may enable gates 14 and 15 for reiterative effects while a key is depressed.
Another feature of the circuitry including note played detector 7 and sample and hold circuits, is simulation of portamento, i.e., a smooth or continuous transition from one tone to another, in response to keys 2 being played legatissimo. If the keys are played staccatissimo there is no portamentation. The portamento effect is selectively provided by including in the sample and hold circuit 8 an electronically controlled switch that selectively short circuits a charging resistor for a storage capacitor responsive to the note indicating volt- .age supplied to the sample and hold circuit. If the keys are played legatissimo, note played detector 7 derives a control signal that open circuits the switch, whereby the storage capacitor is charged at a relatively slow rate through the charging resistor to provide a slow transition of the voltage controlling V.C.O. 9. In response to staccatissimo, note played detector 7 derives a control voltage that closes the switch to short circuit the charging resistance. Thereby, the voltage across the storage capacitor changes between voltages in discrete steps and the frequency of-the oscillator is accordingly altered.
Another tonal effect provides for automatically flatting a note, i.e., reducing its frequency, as it is initially being voiced, to provide accurate simulation of certain instruments, particularly brasses. The amount of flatting is directly responsive to the note associated'with the depressed key. To these ends, the output voltage of sample and hold circuit 8, indicative of the pitch of the depressed key, is coupled to filters 1l,and thence selectively fed to V.C.O. 9 for a transient period when a new tone is being voiced. During the transient period the depressed key indicating voltage reduces the frequency of the V.C.O. to simulate the flatting effect.
The output of wave shaper 22 is fed via a voltage controlled filter 13 and volume control circuit 23 to the input of pre-amplifier 17 and thence via power amplifier 5 to loudspeaker 6. The outputs of filters 11 and 12, as coupled through gates 14 and 15, proceed via volume control circuit 16 to preamplifier 17, the gain of which is controlled as a direct function of depression of expression pedal 18 so that as the pedal is depressed, gain and loudness are increased.
Voltage controlled, active filter l3 selectively provides a number of different effects on the tonal output signal of wave shaper 22. Filter 13 includes low pass, band pass, and high pass two pole transfer functions that are provided, either singly or in parallel combinations, for the signal derived from wave shaper 22. The Q and resonant frequency of all three transfer functions are the same. The Q is preset by the musician, while the resonant frequency may be selectively controlled by any of: the played note indicating voltage derived from sample and hold circuit 8, the gating envelope characteristic supplied to gate 14, or the position of expression pedal 18. The resonant frequency increases as the 1 played note frequency increases, or with increased depression of expression pedal 18, or as the amplitude of the gating envelope increases.
KEY SWITCHES, NOTE PLAYED DETECTOR,
' AND SAMPLE AND HOLD vCIRCUIT, FIG. 2
Reference is now made to FIG. 2 of the drawing wherein there is illustrated a circuit diagram for the elements included in keyboard 2, voltage divider 3, note played detector 7 and sample and hold circuit 8 of FIG. 1. As in the copending application, the voltage derived on lead 24 is indicative of the highest note selected at a particular time, due" to the nomenclature assigned to key switches 31, diodes 32 and the values of resistors 33 in voltage divider 3 Voltage divider 3 is connected to a positive d.c.' source at terminal 34. Higher notes are associated with higher voltages.
The note indicating voltage on lead 24 is applied through blocking diode 35 to the base of NPN emitter follower transistor 36. Across emitter load resistor 37 of transistor 36 there ,is developed a voltage directly proportional to the voltage on lead 24. The voltage across emitter load resistor 37 is fed in parallel to conventional monostable multivibrators 38 and 39 which respectively function as note played and note release detectors.
Monostable multivibrator'38 includes NPN transis-- tors 41 and 42 respectively normally biased to the off The collector of transistor 42 is connected to the base of NPN transistor 49, which is driven into saturation'in response to the positive 20 millisecond pulse being derived at the collector of transistor 42. The collector of transistor 49 is connected through resistor 51 to be biased by the dc voltage at the emitter of transistor 36. Thereby, in response to none of keys 31 being closed, which results in transistor 36 being cut off, a zero emitter voltage of transistor 36 is fed to the collector of transistor 49, and the voltage at the collector of transistor 49 is maintained substantially at ground level. In response to any one of keys 31 being closed, the resulting positive voltage on lead 24 causes transistor 36 to conduct sufficiently to cause the emitter voltage thereof to increase to a level sufficient to bias transistor 49 into a state enabling it to be selectively cut off and driven into saturation in response-to a pulse from monostable multivibrator 38. Thereby, in response to none of the switches 31 being closed or in response to a key switch being closed for less than 20 milliseconds, the voltage developed at the collector of transistor 49 is maintained substantially at ground. milliseconds after a key switch 31 closure, the collector voltage of transistor 49 jumpspositive in response to monostable multivibrator 38 changing state. The voltage developed atthe collector of transistor 42 is normally at a relatively low level and jumps to a high level for the 20 milliseconds immediately after closure of a key switch 31; afterthe 20 millisecond period has elapsed, the voltage at the collector of transistor 48 returns to its low level.
-tor 55 by the emitter of transistor 36 via an ac. coupling network including capacitor 59 and resistor 60. In response to the highest pitch note being released, as indicate d by a decreased voltage on lead 24 and at the emitter of transistor 36, a negative pulse is supplied to the base of transistor 55 to drive that transistor into a cutoff condition, whereby transistor 56 is driven to a conducting condition, Transistors 55 and 56 remain in this condition for approximately 40 milliseconds, after which time they return to their normal state. Thereby,
- for 40 milliseconds after a key is released, positive and negative pulses are'respectively derived at the collectors of transistors 55 and 56.
The positive going, trailing edge of the 40 millisecond pulse at the collector of transistor 56 is coupled through capacitor 48 and resistor 47 to the base of transistor 41 to change the state of monostable multivibrator 38. This positive going, trailing edge has'the same effect on monostable multivibrator 38 as a positive pulse fed to the monostable multivibrator from emitter resistor 37, causing an additional 20 millisec- 0nd delay for a total of 60 milliseconds.
The positive going voltage developed at the collector of'trans'istor 49'is utilized to gate tonal signals from preset voice filters l1, flute filters 12 and waveform shaper 22 intooutput circuitry. Thereby, there is a delay provided for all 'voices so that if a number 'of keys are struck within'20 milliseconds, the tones associated with only the highest pitch key are propagated even though the highest pitched key was not actually first struck. If a number of keys are released within 40 milliseconds of each other, while one or more keys remain activated, the tones for only the highest pitch key still depressed are propagated even though the different keys are released at different times Also, if all of the keys are substantially simultaneously released, no positive going pulse is derived at'the, collector of transistor 49 causes a gating of the outputs of filters 11, 1,2 and 22 such that only the previously voiced key tones are propagated, regardless of the order in which the keys are released.
To control selective decoupling of the note indicating'voltage on lead 24 to storage capacitor 71 of sample and hold circuit 8, the voltages at the collectors of transistors 42 and 56 are'fed to a flip-flop including NOR gates 72 and 73. Output terminals of NOR gates 72 and 73 are do. cross coupled in a conventional manner. One input of NOR gate 72 has a dc. connection to the 10 collector of transistor 42, while one input of NOR gate 73 has a dc connection to the collector of transistor 55. In response to the collector of transistor 42 changing from a low to a high positive dc. voltage, the output of flip-flop 70, derived at the output terminal of NOR gate 73, is driven to a binary one, relatively high voltage state. In contrast, a positive voltage at the collector of transistor 55 causes flip-flop to be driven so that the flipflop output has a relatively low binary zero voltage level. Thereby, in response to a key being struck,
the 20 millisecond pulse developed at the collector of transistor 42 activates flip-flop 70 so that a positive voltage is derived from the output of NOR gate 73; the positive voltage is maintained until the flip-flop state is altered in response to a positive voltage being derived at the collector of transistor 55, as occurs when a highest pitch key switch 31 is released.
In response to a positive or binary one voltage being derived from the output of gate circuit 73, storage capacitor 71 of sample and hold circuit 8 is connected to be responsive to the note indicating voltage on lead 24. To these ends, the positive voltage derived at the output of NOR gate 73 drives normally cutoff NPN transistor 74 into a conducting state The collector of transis to'r 74 is connected to gate electrode 75 of field effect transistor (FET) 76 which functions as a first voltage controlled switch of sample and hold circuit 8. In response-to transistor 76 being activated into a conducting state, current is drawn from .the voltage on lead 24 is fed through input circuit 77 and the source drain path of PET 76 to storage capacitor 71. Thereby, changes inthe voltage on lead .24 are coupled tocapacitor 71 as long as NOR gate 7.3 is deriving a voltage indicating thata note is being played.
In response to.a highest pitch note being released, while another note is still being played, capacitor 71 is momentarily decoupled, for 40 milliseconds, from the voltage on lead 24. Momentary decoupling of capacitor 71 occurs in response to transistor 74being driven into cutoff by the output of NOR gate 73 returning to a bi nary zero level in response to the 40 millisecond positive pulse derived at the collector of transistor'SS. After the 40 millisecond'period has elapsed, the state of monostable multivibrator 38 is altered, whereby a'positive pulse is derived at the collector of transistor 42. The positive pulse is coupled to the input of NOR gate 72, causing flip-flop 70 to change state back to the binary one condition.- lnresponse to the flip-flop'70 being returned to the binary one state, FET'76 again switches to a'closed state and capacitor 71 is charged to the voltage of lead 24. Thereby, transient changes in the release of key switches 31, while one note remains depressed, are decoupled from capacitor 71 and the capacitor is responsive only to the voltage on lead 24, 40 milliseconds after-the release has been performed.
The voltage on capacitor 71 is maintained fixed at a value corresponding with the highest pitch note after all keys are released because FET 76 is open circuited gate electrode 75 to bias FET 76 into a conducting state.
in response to all keys being released. To these ends,
I normally cut off NPN transistor 81 has its base connected to lead 24. In response to any of key switches vput voltage. of NOR gate 73 controls the conducting state of transistors 74 and therefore FET 76. If none of key switches 31 is closed, transistors 81 and 84 are respectively biased to the off and on states, whereby transistor 84 shunts the emitterbase path of transistor 74 to hold transistor 74 in a. cutoff concondition and prevent FET 76 from conducting. I
In summary, in response to a key switch 31 being closed, FET 76 is closed, whereby capacitor 71 is charged to the voltage on lead 24, causing voltage controlled oscillator 9 to oscillate at the frequency determined by the'voltage on lead 28. In response to a note being released which causes a voltage on lead 24 to detor 71 is maintained at the level corresponding with the previous highest pitch played note. If there is still a note depressed after the 40 millisecond period, the voltage corresponding with the new, lower pitch note is fedthrough FET 76"to capacitor 71. The voice correspond- .ing'with the new note is sounded milliseconds after the voltage corresponding withthe note is stored on capacitor 71, by virtue of'the positive going voltage derived at the collector of transistor 49. If during the 40 millisecond delay period associated with note release detector 39,'a new note is played which causes the voltage on lead 24 to increase, FET 76 is immediately closed and the voltage across capacitor 71 is driven to the "new value. 20 milliseconds after the new, higher pitch note has been'played, a positive goingpulse is derived at the collector of transistor 49 to enable tones associated with the new note to be derived.
A further feature of sample and hold circuit 8 is simulation of portamento. To these ends, the source drain path of PET 7.6 is connected to capacitor 71 through variable resistor 91- that is connected across the source drain path of FET 92, which functions as anelectronic switch in response to the output voltage of monostable multivibrator 93, included in note played detector 7. In response to legatissimo playing,as detected in a manner described infra, the source drain path of FET 92 is open circuited, whereby capacitor 71 is charged through resistor 91. In response to staccatissimo playing, the source drain path of FET 9.2 functions as a short circuit for resistor 91, whereby the voltage of castantaneou sly. In response to instantaneous step changes in the voltage of capacitor 71, the frequency of oscillator 9 is stepped. In contrast, a slow variation in the change in the frequency of oscillator 9 occurs in response to a smooth transition of the .voltage across capacitor 71. The charging rate for capacitor 71 while portamento occurs is selected by the musician adjusting the value of resistor 91 to achievethe desired rate of change in the frequency of oscillator 9.
Detection of the legatissimo playing is provided by connecting the input of monostable multivibrator 93 to the collector of transistor 81 through an ac. coupling circuit comprising capacitor 94 and resistor 95. Monostable multivibrator 93 includes NPN transistors 96 and 97 respectively normally biased to the conducting and non-conducting states. The collector of transistor 97 is connected to the base of transistor 96' by capacitor 98 and resistor 99, having values selected so that monostable multivibrator 93 derives an 8 millisecond pulse in response to each negative transition'at the collector of transistor 81. Thereby, each time a new set of keys is depressed while no other keys are depressed, monostable multivibrator 93 is activated to derive an 8 millisecond negative pulse at the collector of transistor 97. The negative pulse is dlc. coupled to the gate 100 of FET 92, causing the FET to be driven into a conducting state, short circuiting resistor 91. Thereby, in response to all keys of one set of keys being released prior to any keysofa second set being depressed (i.e., staccatissimo note playing), capacitor 71 is instantly charged to the voltage associated with the new note on lead 24. If,
however, the notes are played so that one key is not released until a second key has been depressed (legatissimo note-playing), negative pulses are not derived at the collector of transistor 97 and a highimpedance path exists through resistor 91- to capacitor 71 to provide gradual voltage change. i
MODE SELECTOR-FIG. '3
trated in circuit diagrams associated with the particular circuits. I
Mode selector 1 9 includes a monostable multivibrator 101 comprising NPN transistors 102 and 103. The collector of transistor-103 is connected to the base of transistor 102 through a series circuit-including resistor 104 and capacitor 105, having valves selected so that the monostable derives a short duration pulse, on the order of 8 milliseconds, in response to normally cut off transistor 102 being driven into a conducting state in .pacitor 71 is changed in discrete steps, substantially in- I response to a positive pulse being applied to its base. The resulting, short duration pulse derived-at the collector of transistor 103 is coupled to the base of inverting NPN transistor 106, the collector of which is connected to the base of PNP transistor 107 which is normally biased into a cut off condition. Transistor 107 is activated into a conducting state in response to transistor 106 being driven into a conducting state, whereby transistor 107, when turned on, functions as a constant current source. To provide different attackrates the current derived from the collector of transistor 107 is controlled by varying the impedance of the transistor emitter circuit. In a slow attack configuration, the emitter of transistor 107 is connected to a positive +30 volt d.c. source through 4.7K resistor 108, and in a fast attack configuration, while switch 111 is closed, the emit- 13 ter of transistor 107 is connected to the +30 volt source through theparallel combination of resistor 108 and 1K resistor 109, whereby the current of the second configuration is approximately five times that of the first.
The constant current derived from the collector of transistor 107 is applied to a pair of'ramp forming networks 112 and 113 which are connected to trigger inputs of gates 14 and 15, respectively; the ramp derived from network 112 is also applied as an enabling input to the gate of wave shaper22. Each of networks 112 and 113 includes the parallel combination ofa capacitor and a resistor; thecapacitor and resistor of network 112 preferably have values of one microfarad and 2.2M, an the capacitor and resistor of network 113 preferably have values of approximately 0.05 microfarads and 100K. so that the charging and discharging rates of the former are considerably less than the latter. The voltage across network 112 is decoupled or isolated from the voltage developed across circuit 113, by virtue of diode 114, the anode of which is connected to network 113, and the cathode of which is connected to network 112.
To control the-decay rate of'the ramp voltage derived from circuit 112 and thereby provide a sustain effect, potentiometer 114 is connected to circuit 112 via-coupling resistor '1 and isolation diode 115a. Potentiometer 114 is selectively connected to a +30 volt d.c. source by switch 116. The position of slider 117 of potentiometer 114. controls the decay rate of the trailing edge of the ramp voltage derived by circuit 112.
The conducting state and current magnitude of transistor 107 are determined by the system mode of operation, asis the'presence or'absence of the sustain effect, as derived across network 112. In response to the system being in a percussive mode, transistor 107 is acti vated into a' conducting state for an 8 millisecond period in response to each positive going transition at the collector of transistor 49, FIG. 2, and switch 111 is closed so that a relatively large current is derived from transistor 107. The relatively large current derived from transistor 107 caused capacitors of circuits 112 and 113 to be quickly charged to a relatively high voltage, to provide fastattack and rapid opening, i.e., enabling, of gates 14, 15 and the gate of waveform shaper 22. These results are achieved by connecting the collector of transistor 49 to the base of normally cut off transistor 102 through an ac. coupling network comprising capacitor 118 and resistor 119.
After the 8 millisecond on-time of transistor 107 has elapsed, the enabling voltages supplied by circuit 112 to gate 14 and wave shaper 22 and the enabling voltage supplied by circuit 113 to gate 15 decrease. Because of the relatively small resistor and capacitor circuit 113, the decay of the voltage supplied to gate 15 is relatively fast, to cause relatively rapid cutoff of gate 15. In contrast, the resistor and capacitor of circuit 112 are selectedto enable a sustain effect to be provided. In the percussive mode, the sustain duration is variably controlled by adjusting the position of slider 117 and closing switch 116. With the position of slider l 17 adjusted toward the top .of slider 114 a relatively long sustain effect is provided, whereby gate 14 and wave shaper 22 remain activated for an appreciable time period to simulate the sustain effect of a percussive instrument.
In a second mode of operation, the continuous mode, gates 14 and 15 and the gate in wave shaper 22 are enabled 20 milliseconds after any of key switches 31 are depressed and remain enabled until all keys are re leased. To these ends, the collector of transistor 49 is connected via a dc path to the base of transistor 102 through resistor 119 and switch 121 which shunts capacitor 118 and is closed when the system is operated in a continuous mode. In response to any of key switches 31 being depressed for more than 20 milliseconds, a positive voltage is derived atthe collector of transistor 49 and is coupled through switch 121 to drive transistor 102 into a conducting state. Transistor 102 remains in the conducting state as long as a positive voltage is applied to its base, whereby transistor 107 is biased into a conducting state to supply constant current to circuits 112 and 113; thereby, gates 14, 15 and the gate in waveform shaper 22 pass tone signals supplied to them as long as any of key switches 31 are depressed. In the continuous mode, the attack rate can, at the option of the musician, be either slow or fast by opening or closing switch 111. Similarly, by closing an opening switch. 116, the sustain effect can be a relatively long controllable time or a fixed shorter time for tones fed through gate 14 and the gate of wave shaper 22.
In the reiterative mode, fast attack enabling voltages are derived from circuits 112 and 113 periodically, at a frequency determined by the modulation oscillator 20 (FIG. l), for as long as the key switches remain activated. To thesev ends, switch 111 is closed and the base of transistor 102 is ac coupled by series connected resistor 119, capacitor 122 and switch 123 to be. responsive to square waves derived by modulation oscillator 20. Switch 123 is closed by the musician when the system is in the reiterative mode, at which time modulation oscillator 20 is adjusted to derive a random frequency output, whereby monostable multivibrator 101 derives an 8 millisecond pulse in response to each positive going transistion of the modulation oscillator output square wave. Enable voltages are derived by circuits 112 and 113 in response to monostable multivibrator 101 being triggered by square wave input in the same manner as described for activation of the multivibrator in response to the positive going trailing edge of the voltage derived at the collector of transistor 49.
WAVEFORM SHAPER 22, FIG. 4
The circuit of FIG. 4 responds to the tones derived from the 8', l6 and 32' outputs of frequency divider chain 10 to selectively synthesize sawtooth voltages, pulses and square waves having the same fundamental frequency as the selectively coupled tone input signals. The duration of the pulses is dependent upon the note of the highest pitch key. The derived square waves are substantial replicas of the input square waves. The different waveforms derived in response to the square wave tones fed to FIG. 4 enable unusual tonal effects to be attained and different musical instruments to be simulated; for example, the sawtooth, pulse and square waves can be utilized to respectively simulate piano, oboe and clarinet instruments. These waveforms can be selectively modified by voltage controlled filter 13 to provide otherunusual effects. Waveform shaper 22 is also selectively responsive to random, i.e., noise signals, as well as a pulse each time the state of monostable multivibrator 38, FIG. 2, is changed in response to a new high note signal level being derived on lead 24. The noise input can simulate acoustic effects of, for example, the wind, surf, or a brush hitting a snare, while the .pulse derived from monostable multivibrator 38 can provide click effects or noise.
Control of which one or combination of the 8', 16'
or, 32 tones from frequency divider chain 10 into waveform shaper 22 is provided by selectively forward biasing diodes 131, 132 and 133, having cathodes respectively connected to the 8, 16 and 32 outputs of frequency divider chain 10. Diodes 131-133 are selectively forward biased by applying positive voltages to anodes thereof in response to closure of normally open switches 1-34, 135 and 136, which are respectively connected to the diode anodes via resistors 137 so that a- +5 volt d.c. level at terminal 138 can forward bias the diodes. The tone signals fed through diodes 131-133 are fed in parallel to wave synthesizing networks 141, 142 and 143, which respectively enable selective-derivation of sawtooth, pulse and square waves.
Sawtooth wave generator 141 includes NPN transistors 144 and 145 which are responsive to the square wave inputs fed through diodes 131-133 to derive a pulse having awidth indicative of the footage passed by the diodes. To these ends, the anodes of diodes 131, 132 and 133 are connected, via capacitors 146, 147 and 148, to the base of transistor 144 which is normally forward biased by the connection of resistor 150 to the +30 volt d.c. source at terminal 149. The values of capacitors 146, 147 and 148 are selected in conjunction with the value of resistor 150 to provide an on-time for pulses derived byqtransistor 144 such that the pulse width is directly related to the footage of the input tone, 'i.e., the pulse width for the 8' tone is narrower than the pulse widths for the 16 and 32' tones.
Transistor 145 is selectively maintained in a saturated, forward biased condition by connecting its base to the +30 volt supply at terminal 149 through resistor 152 and switch 153, which is opened by the musician .when he wants to synthesize sawtooth-type waves.
When switch 153 is closed the collector of transistor 145 is grounded, whereby the base of transistor 144, which is shunted by the collector of transistor 145, cannot be forward biased and sawtoothed variations cannot be derived. v
To enable the sawtooth, as well as the other waveforms derived by the waveform shaper 22 to be derived, gating NPN transistor. 153 is provided. The base mode. In response to the base of transistor 153 being forward biased, current flows from the +30 volt source connected to the transistor collector, to the transistor emitter and thence to the collector of transistor 144 via resistor 154, to enable current to be delivered to the collector of transistor 144.
In. operation, negative going transitions of the square waves coupled to the base of transistor 144 from the anodes of diodes 131-133 drive transistor 144 into a cut off condition. Transistor 144 remains in a cut off condition until the voltage across the capacitor 146, 147 or 148 responsive to the square waves fed through the forward biased one of diodes 131-133 reaches a voltage sufficient to activate transistor 144 into a saturated state. Thereby, thecut off duration is determined by the values of capacitors 146-l48and resistor 150, whereby a positive voltage is derived at the collector of transistor 144 for a time, period indicative of the footage fed to the base of transistor 144 and the widths of generated pulses are accordingly controlled. The frequency of the generated pulses equals the frequency of the input square waves.
The voltage at the collector of transistor 144 is fed to an integrating circuit including resistor 158 and capacitor 159. In response to the. positive voltage being derived at the collector of transistor 144, capacitor 159 is charged and the capacitor is subsequently discharged through the emitter collector pathof transistor 144 in response to the transistor returning to a saturated condition. The time duration of the increasing ramp derived by the integrating capacitor 159 is determined by the duration of the pulse derived at the collector of transistor 144, while the decay rate of the sawtooth wave derived from the integrating capacitor is substantially constant. Thereby, the leading edge duration of the sawtooth wave is controlled by which of footage is fed through diodes 131-133, while the sawtooth frequency equals the fundamental frequency of the square and 166 which are interconnected with each other, as.
well as the tone signal and power supply voltages, in a manner similar to the connections of transistors 144 and in particular, the base of transistor is connected to the anodes of diodes 131, 132and 133 by capacitors 167, 168 and- 169, having values selected with criteria similar to those for determining the values of capacitors 146-148. The charging rate of capacitors 167-169 is controlled by the amplitude of the highest note indicating voltage on lead 24, which is d.c. coupled to the base of transistor 165 via terminal 171 and resistor 172 to control the extent of base forward bias of the transistor. In response to variations in the amplitude of the voltage at terminal 171, the cut off time of transistor 165 is varied. In response to a negative going pulse being supplied through one of diodes 131-133 and capacitors 167-169, to the base of transistor 165, the transistor is driven into cut off and remains cut off until the voltage across one of capacitors 167-169 reaches a level sufficient to cause the transistor to be forward biased and driven into saturation, which occurs at a time controlled by the voltage on terminal 171, value of resistor 172 and which of the capacitors is responsive to the square wave input.
To enable transistor 165 to be selectively activated and cut off to provide derivation of the pulses, switch 173 is connected between a positive dc power supply voltage and the base of transistor 166. in response to switch 173 being closed, the emitter collector path of nal 164 via a pulse. shaping circuit including diode 175 which is connected to load resistor 176, the voltage across which is coupled to the output terminal via a low impedance a.c. coupling circuit comprising capacitor 177 and resistor 178.
The derivation of replicas of the square wave voltages selectively coupled th rough diodes l3l-133 is performed with circuit 143, that includes NPN transistors 179 and 181, connected in a manner similar to transistors 165 and 166. The base of transistor 179 and collector and transistor 181 are connected to the anodesof diodes 131, 132 and 133 by a dc. path including diodes 182 and current limiting resistors 183; the cathodes of diodes 182 are connected to the base of transistor 179 to isolate the base from negative transients that might be derived from capacitors 146-148 and 167-169. Square wavesare derived at the collector of transistor 179 by the musician opening switch 184, and are fed through the circuit including diode 175, re-
sistors 176 and 178 and capacitor 177 to terminal 164 in response to current being supplied to the collector of transistor 179 by the emitter of transistor'153.
The noise signal from noise generator 21 is selectively coupled to output terminal 164 under the control of the states of transistor 153 and switch 188. To this end, the output signal of noise'generator 21 is fed to the base of NPNtransistor 185 via an a.c. coupling circuit includingcapacitor 186 that is connected to the noise l8 sponse to the emitter collector path of transistor 195 being biased into a conducting state'by the musician closing switch 196 that selectively connects the positive dc. power supply voltage to the base of transistor 195.
VOLTAGE CONTROLLED OSCILLATOR AND CONTROL CIRCUITRY THEREFOR,
Reference is now made to FIG. 5 of the drawing wherein there is illustrated a circuit diagram of voltage controlled oscillator 9 and control circuitry therefor. The voltage controlled oscillator basic circuitry is substantially the same as that disclosed in my previously mentioned copending application, so that a detailed desource. Transistor 185 is normally forward biased by I the connection of its base to'the plus dc. power supply through resistor 187. Forward bias for the base emitter junction of transistor 185 is removed by closing switch 188, which caused normally cut off transistor 189 to be forward biased and shunt the emitter base junction of transistor 185, thereby driving transistor 185 to cut off. In response to switch 188, however, being open circuited, the noise input signalis fed to terminal 164 via diode-175, resistors 176 and 178 and capacitor 177 when transistor 153 is conducting, by virtue of the dc. connection between the collector of transistor 185 and the emitter of transistor 153.
To-derive a relativelyfshort duration pulse each time 7 a new highpitch key is struck, the base of NPN transistor 191 is a.c. coupled via capacitor 192 and resistor 193 to the collector of transistor 42 of note played detecting multivibrator '38, FIG. 2. Transistor 191 is normally biased to a conducting state bythe connection of its base to the positive dc. power supply via resistor 194. In response to the trailing, negative going edge of the pulse derived at the collector of transistor 42, which occurs 20 milliseconds after rnonostable-multivibrator 38 isdriven into a transient state in response to a new high note being struck, transistor 191 is driven to cut off and a positive pulse is supplied to terminal 164 through diode 175, resistors 176 and 178 and capacitor 177. The duration of the pulse is determined by the values of capacitor 192 and resistor 193, components which control the length of time transistor 191 remains cut off. The pulse can be derived only when transistor 153 has been driven into a conducting state. To prevent the pulses derived in response to each activation of monostable multivibrator 38 being coupled to output terminal 164, the emitter base junction of transistor 191 is selectively shunted. Shunting occurs in rescription of the transistors, associated resistors and ca,- pacitors is not required herein. The frequency of oscillator 9 is controlled, inter alia, by the amplitude of the d.c., note indicating voltage derived from the output of sample and hold circuit 8, which is do. coupled to oscillator input terminal 201'. The frequency of the oscillator is also controlled by the magnitude of: the positive dc. power supply voltage at terminal 202, a variable voltage at terminal 203, the value of resistor 204 which feeds the voltage at terminal 201 to the oscillator, and the values of substantially equal capacitors 205 and 206 that cross couple the collectors and bases of the oscillator transistors together.
The square wave output frequency of the oscillator, as derived at its output terminal 207, which is connected as an input to frequency divider chain 10, is expressed as:
f,, output frequency,
V, input voltage at terminal 201,
V, DC. power supply voltage at terminal 202,
V, voltage at terminal 203,
= value of resistor 204,
C value of each of capacitors 205 and 206. From Equation (1), since V is greater than V, the frequency of oscillator 9 is related to variations in the amplitude of the voltage V,. in such a manner that as the voltage at terminal 203 increases, the outputfrequency increases. The voltage at terminal 203 is selectively varied in response to the output of modulation oscillator 20 and to provide flatting effects for certain musical instruments, particularly brasses, which are flatter when first voiced than in a steady state condition. Vibrato modulation of the frequency of oscillator 9 is attained by feeding the output of modulation oscillator 20 to terminal 203. The frequency of modulation oscillator 20 can either be fixed in the range between approximately 1 to 50 Hertz, normally adjusted for a vibrato rate of approximately 7 Hertz, or randomly varied about a means frequency within this range. In responseto the periodic or random variations in the amplitude of the wave derived by modulation oscillator 20, the frequency of oscillator 9 is modulated.
The flatting effect is a transient function of the note indicating signal fed by voltage divider 3 to lead 24. As the pitch of the note increases, the flatting effect is decreased. To these ends, the voltage at terminal 201, in-
dicative of the highest note resulting from depression of key switches 31, is selectively gated to terminal 203 at a time when the tone corresponding with the note is initially being sounded.
For a realistic simulation of the different brass tones, the amount of flatting necessary is different for different instruments. For example, a trombone is initially voiced flatter than a trumpet, whereby it is necessary to have more flatting when simulating a trombone than for simulationof a trumpet. When it is desired to provide the flatting effect for one of the instruments, one of several different positive d.c voltages is applied to the emitter of PNP transistor 209 by closing one of switches 211 or 221 which are connected to a positive d.c. supply voltage at terminal 212 through resistors 210 and 222 having different values. If switch 211 and resistor 210 are provided for trumpet flatting and switch 221 and resistor 222 for trombone flatting, the value of resistor 222 is smaller than that of resistor 210 to provide a higher emitter current for the trombone and therefore greater trombone flatting.
In response to one of switches 211 or 221 being closed, the difference in voltage amplitude between the note indicating voltage on lead 201 and the emitter voltage of transistor 209 is derived at the collector of transistor 209 which is connected to ground via load resistor 213 that is shunted by the normally cut off emitter collector path of NPN transistor 214. Transistor 214 is driven into a conducting state in response to the positive going trailing edge of the voltage developed at the collector of transistor 49, which is fed to the transistor base via the a.c. coupling circuit including capacitor 215 and resistors 216 and 217. A terminal common to the collectors of transistors 209 and 214 is connected to terminal 203 and across relatively small load resistor 208 via relatively large capacitor 218. When transistor 214 is cut off, capacitor 218 is charged to a voltage which is dependent upon the emitter current of transistor 209 and the value of resistor 213 so that as the highest note indicating voltage, V increases the voltage on capacitor 218 decreases.
In response to transistor 214 being transiently activated into a conducting state in response to the positive going, trailing edge transition derived from the collector of transistor 49, capacitor 218 is suddenly discharged through the collector-emitter path of transistor 214. Thereby, the voltage at terminal 203 suddenly decreases by an amount equal to the voltage on capacitor 218 and therefore related to the value of V,,. This applies a negative transient voltage at terminal 203 which causes oscillation to transiently go flat. Capacitor 218 exponentially recharges after transistor 214 returns to a non-conducting state. Because the amplitude of the sudden decrease in the voltage at terminal 203 is inversely related to the highest note, greater flatting is provided for lower pitch tones than for higher pitch tones.
BRASS PRESET VOICE FILTERS, FIG. 6
Reference is now made to FIG. 6 of the drawing wherein there is illustrated a circuit diagram of a complete channel 231 for simulation of one brass instrument, the trumpet, as well as control circuitry 233 for the trumpet simulation channel and a further channel 232 for simulating a second brass instrument, e.g., the trombone. Trumpet simulation channel 231 is driven by the 16 output of frequency divider chain 10, while the trombone simulating channel 232 is driven by the output of the frequency divider chain. Channels 231 and 232 are driven in parallel by an output signal derived by envelope shaping network 233 which is responsive to the positive going voltage derived at the collector of transistor 49, FIG. 2. Channels 231 and 232 respond to the signals derived by envelope shaper 233 to provide simulation of the attack rate, attack tone color change, tone color change as a function of dynamic level, and overall tone quality for the two brass instruments being simulated.
Attack rate and release rate simulation are the same for the two brass instruments, whereby envelope shaping circuit 233 can be utilized to control envelope modulation of both of channels 231 and 232. The attack and release voltage waveform applied by circuit 233 to channels 231 and 232 is illustrated in FIG. 7, wherein the output voltage of circuit 233 is illustrated as a function of time. During the first few, approximately 6, milliseconds after derivation of the positive going, trailing edge at the collector of transistor 49, the voltage developed by circuit 233 increases at a relatively rapid exponential rate, as indicated by line segment 234. After the 6 millisecond interval has elapsed, the rate of voltage increase of the output of circuit 233 decreases and assumes the exponential relationship indicated by waveform segment 235. Upon release of a note, the waveform derived by circuit 233 decays at a rate indicated by exponential decay wave portion 236.
To enable the wave shape indicated by FIG. 7 to be derived, circuit 233 includes three cascaded NPN transistors 237, 238 and 239 arranged so that the base of each succeeding stage is connected to be driven by the collector of the preceding stage. Transistors 237 and 239 are normally biased to cut off condition, while transistor 238 is normally biased to be conducting.
The base of transistor 237 is do coupled via resistor 241 and terminal 242 to the collector of transistor 49 so that in response to a positive voltage being derived at the collector of transistor 49, transistor 237 is driven from its normally cut off state into a conducting state. The resulting decrease in the voltage at the collector of transistor 237 is coupled to the base of transistor 238, causing the latter transistor to be biased into a cut off state. In response to transistor 238 being cut off, capacitor 243, which in combination with diode 242 shunts the collectoremitter path of transistor 238, is charged by the dc. power supply voltage connected to terminal 244 via resistor 245 and diode 242. Thereby, the voltage across capacitor 243 increases as indicated by the waveform segment 234.
In response to the voltage across capacitor 243 reaching a predetermined level, the charge rate of the capacitor is decreased since resistor 246 and diode 247 are connected in series from the collector of transistor gate a +5 volt d.c. power supply at terminal 248. In