Rhythmic accompaniment system employing randomness in rhythm generation

BACKGROUND OF THE INVENTION

The present invention relates to rhythmic accompaniment systems and more particularly to a selectively actuable rhythmic accompaniment system of the free running type.

Rhythmic accompaniment systems are known in the prior art. Certain of these are free running, that is, they are neither synchronized with nor slaved to the playing of a musical instrument, but rather produce rhythmic accompaniment tones to which the player may conform his tempo. The free running type accompaniment system is contrasted to what has become known as the automatic and semiautomatic accompaniment systems which automatically conform their tempo and/or measure duration to the tempo initiated by the player. The present system is of the free running type and is disclosed in a preferred embodiment along with alternative circuitry for providing certain features. The system may be built into a musical instrument, such as an electronic organ, or may be separate and apart from any musical instrument or instruments with which it might be utilized for rhythmic accompaniment.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention a rhythmic accompaniment system is actuable to function as a free running rhythm system producing selected rhythm patterns in selected tempos and tone voices and is deactuable to permit the operator to completely control the tempo and rhythm pattern. When operating in the free running mode, the system is capable of producing any one or combination of a plurality of rhythms, each rhythm comprising a two measure pattern consisting of two single measure patterns which alternate continuously. Alternatively, the two patterns may be evoked randomly if so elected by the operator. A downbeat lamp flashes on the first beat of each measure, and means are provided to permit tempo selection over a wide range of measures per unit time. Both manual and automatic operation may be employed either separately or together to achieve desired rhythmic effects.

The system utilizes 13 master timing pulses per measure, the pulses being spaced by integral numbers of fixed time units to provide an overall 13 pulse measure of 24 timing units duration. In one embodiment the 13 master timing pulses are derived at corresponding levels of a repetitive ramp waveform, each ramp corresponding to one measure. Alternatively, two ramps are provided during each measure, each ramp producing seven primary pulses of which only six are employed during alternate half-measures to produce the total of 13 pulses per measure. Depending upon the selected rhythm, various ones of these timing pulses are chosen during each measure and applied to selected voice circuits to produce the desired rhythmic sounds.

Some frequently encountered rhythmic patterns extend over two measures. In such patterns the musical part completed by one rhythmic pattern may be the same for all measures, while another voice in the same pattern may be two measures long. For example, in one type of rhumba pattern the part played by the bass drum is the same for each measure whereas the part played by the conga drum is periodic over two measures. In accordance with the present invention, provision is made for automatically alternating two rhythmic measures, and alternatively for randomly evoking two different rhythmic measures. In an alternative embodiment, four pattern modes are actuable by the operator wherein a first or second rhythmic measure may be continuously repeated, the first and second rhythmic measures may be continuously alternated, and the first and second rhythmic measures may be randomly evoked.

A further provision of the present invention permits adjustment of the slope of the timing ramp to permit the operator to control the measure time and hence the tempo of the automatic rhythmic accompaniment.

A further feature of the present invention permits resetting of the timing ramp whenever the system is started to assure that the system always starts on the downbeat or first beat of each measure.

In still another feature of the present invention a novel cowbell voice circuit is provided which gates on a 1 kHz. oscillator and a linear gate for 2 kHz. continuous oscillator, the two signals being combined to provide a realistic cowbell tone.

In still another feature of the present invention certain pulses gated from a rhythm selection matrix are employed to initiate and eventually terminate trigger signals applied to drumsimulating voice circuits to produce drum roll effects over a desired number of beats in each measure.

It is accordingly a broad object of the present invention to provide a novel rhythmic accompaniment instrument.

It is another object of the present invention to provide a rhythmic accompaniment instrument which is capable of providing rhythmic patterns and voices which are more realistic than those produced by prior art instruments of this type.

Still another object of the present invention is to provide a rhythmic accompaniment instrument capable of operation in four different rhythmic measure modes, including continuous alternation of two different rhythmic measures, and the random selection of said two rhythmic measures.

Still another object of the present invention relates to the generation of 13 uniquely spaced master timing pulses from which substantially any desired rhythm pattern can be generated.

Still further objects of the present invention include the generation of cowbell and drum roll rhythm sounds by means of novel circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of spec ie embodiments thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram of a preferred embodiment of the present invention;

FIGS. 2a and 2b taken together comprise a schematic circuit diagram of the timing circuits of the embodiment illustrated in FIG. 1;

FIGS. 3a and 3b taken together comprise a schematic diagram of the rhythm selection matrix employed in the embodiment illustrated in FIG. 1;

FIGS. 4a and 4b taken together comprise a schematic circuit diagram of voice generator circuits utilized in conjunction with the system illustrated in FIG. 1;

FIG. 5 is a timing diagram illustrating various master timing pulses and rhythmic patterns produced in the system of FIG.

FIG. 6 is a schematic diagram of an alternative circuit for producing the master timing pulses required for the system of FIG. 1;

FIG. 7 is a schematic diagram of a portion of an alternative matrix circuit for use in place of the circuit illustrated in FIGS. 3α and b; and

FIG. 8 is a schematic diagram of an alternative circuit to be provided in the system of FIG. 1 to permit four different modes of a rhythmic pattern operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now more particularly to FIG. 1 of the accompanying drawings there is illustrated a block diagram of a rhythmic accompaniment system wherein closure switch SI actuates a repetitive ramp generator 10, the frequency of which is selectively adjustable by means of frequency control element 11. The ramp signal is applied to a timing pulse generator 13 which provides a plurality of master timing pulses on individual signal lines, at each pulse provided at a time corresponding to a respective level of the ramp signal pro

3,629,480

4 vided by generator 10. The master timing pulses occur in a repetitive pattern which comprises a musical measure. The master timing pulses are spaced in time in accordance with the criteria described in detail hereinbelow and are applied to respective lines in a rhythm selection matrix 15. Matrix 15 also receives one or more signals from automatic rhythm selection switches 17, matrix 15 being arranged so that predetermined ones of the timing pulses are provided as output pulses in accordance with which of the automatic rhythm selection switches are actuated. The output pulses from matrix 15 are applied to voice circuits 19 wherein appropriate accompaniment tones are generated in response to each output pulse from the matrix. The generated tones are combined and applied to an amplifier 21 and in turn to loud speaker 23.

Rhythm selection matrix 15 also receives two gating signals from measure alternation control unit 25 which is essentially a bistable device. When unit 25 is in a first state it provides a “B” signal which causes a rhythm selected by switches 17 to be produced in a first rhythmic pattern of output pulses from matrix 15 during each measure. Likewise, when unit 25 is in a second state it provides a “C” signal which causes the selected rhythm to be produced in a second pattern during each measure. The state of the measure alternation control unit 25 is illustrated as being controlled either by downbeat pulse generator 27 or random oscillator 29. Downbeat pulse generator 27 receives the ramp signal from repetitive ramp generator 10 and provides a pulse corresponding to the downbeat or first pulse in each measure. This downbeat pulse lights lamp 31 at the console of the unit and also changes the state of measure alternation control unit 25. Consequently, when downbeat pulse generator 27 is in control of unit 25, the two rhythmic pattern measures produced by signals B and C will alternate. Random oscillator 29, when effective, changes the state of unit 25 at a frequency which is random with respect to the frequency of repetitive ramp generator 10 so that the measures produced by signals B and C at matrix 15 change randomly, that is, not in regular measure alternation.

The Roll oscillator output is fed to the Roll control unit 32 which responds to appropriate output pulses applied thereto from matrix 15 to apply a return Roll signal to the matrix. This signal gates one or more input signals to the voice circuits 19 for a predetermined period of time between two master timing pulses supplied by generator 13. During this predetermined period of time the appropriate voice circuit simulates a drum roll as opposed to the relatively short percussive sound produced by the usual output pulse for matrix 15.

Voice circuits 19 may be actuated manually, either in conjunction with or independently of automatic voice circuit actuation, by appropriately actuating various ones of manual rhythm switches 33. If for example, the clave manual switch is closed, each pedal actuation at console unit 35 initiates a trigger pulse, via trigger circuit 37, which passes through the pedal clave switch at unit 33 to trigger the clave voice circuit. Actuation of a key at unit 35 likewise initiates a trigger at circuit 37 which passes through the appropriate accompaniment rhythm switch to trigger an appropriate voice circuit at unit 19.

The system of FIG. 1 is illustrated in greater detail in FIGS. 2a, 2b, 3a, 3b, and 4a and 4b. With particular reference to FIG. 2α, repetitive ramp generator 10 of FIG. 1 comprises a variable resistor Pl connected in series with fixed resistor R5 between +28 volts DC and the emitter electrode of PNPtransistor QI. The collector of QI is connected via resistor R1 to the base of NPN-transistor Q3 which, along with QI, comprises a monostable multivibrator. The emitter of Q3 is connected directly to ground and its base is connected to ground via resistor R2. The center arm of variable resistor Pl is connected via resistor RS2 to the emitter of y PNP transistor Q2, the base of which is connected to +22 v. and the collector of which is returned to ground via timing capacitor Cl. The collector of Q2 is also connected to the base of NPN-transistor Q4, the emitter of which is connected to the base of further NPN-transistor Q5. The emitters of Q4 and Q5 are returned to —50 volts DC through respective resistors R10 and Rll. Transistors Q4 and Q5 and resistors R10 and Rll comprise a compound emitter follower circuit which serves to buffer the linear ramp applied to the base of Q4 from the threshold ⁵ switching circuits Q6-Q13 connected to the emitter of Q5.

Also connected to the collector of Q2 is a resistor R6 which is also connected to the collector of Q3 via diode DI and to a one-half measure bistable circuit, to be described in detail below, via diode D2.

The collector of Q3 and the base of 01 are connected via a series connected resistor R4 and capacitor C2. The collector of 03 and the emitter of 01 are connected via resistor R3 at +22 v.

Transistor Q2, in conjunction with resistors RS2, Pl, and R5, comprises a constant current generator, the current from which flows from the collector of 02 at a level depending upon the setting of Pl. The constant current charges timing capacitor Cl to produce the required linear ramp of voltage at 2₀ the base of transistor Q4; that is, if Cl is initially uncharged, the voltage thereacross increases linearly.

The linear ramp voltage, which also appears at the emitter of Q5, is applied in parallel to each of resistors R12 through R19, inclusive. Each of R12 through R19 feeds the base of a 25 respective NPN-transistor Q6 through Q13 which are connected to progressively increasing (in a positive sense) emitter potentials. More particularly, resistors RSI and R20 through R33 inclusive comprise a complex voltage divider network connected between R5 and ground from which various taps 30 are connected to the emitters of Q6 through Q13. The potentials connected to the various emitters vary in accordance with a desired pulse timing sequence such that normally nonconducting transistors Q6 through Q13 are gating or. at times corresponding to predetermined voltage levels of the ramp ap35 pearing at the emitter of Q5. Nonconduction of Q6 through Q13, in the absence of the ramp voltage at the emitter of Q5, is assured by virtue of the slightly negative voltage appearing at the emitter of Q5 via resistor Rll.

The collectors of Q6 through Q12 are AC coupled via 40 capacitors C3 through C9 inclusive to the bases electrode of respective NPN-transistor switches Q14 through Q20, inclusive. Transistors Q14 through Q20 have their emitters returned to ground and are biased to normally conduct from +28 volts DC through their collector-emitter circuits through 4$ respective collector resistors R51 through R57. This biased-on condition is accomplished by means of +28 volts DC applied to the bases of Q14 through Q20 via respective base-bias resistors R44 through R50. The collectors of each of transistors Q14 through Q20 are connected to the anode of respective diodes D5 through Dll, the cathodes of which are tied together and connected to the collector of NPN-transistor Q31. The operation of Q31 is described in greater detail subsequently; however, for present purposes it is to be understood 55 that when Q31 conducts, diodes D5 through Dll shunt the collectors of Q14 through Q20 to ground and render them unable to provide positive-going output pulses.

As the ramp voltage at the emitter of Q5 increases, Q6 through Q12 are sequentially turned on. The transition from 6Q off to on of each of these transistors transmits a corresponding negative-going pulse via coupling capacitors C3 through C9 to the base of the appropriate transistor Q14 through Q20, rendering the latter momentarily nonconductive. The nonconductive intervals from Q14 through Q20 produce positive65 going primary pulses at the collectors of these transistors, assuming of course that transistor Q31 is not conducting and therefore diodes D5 through Dll do not shunt the collectors to ground. Sometime after Q12 is turned on by the ramp signal, Q13 is also turned on, causing QI to conduct. This ef70 fectively fires the monostable circuit comprising QI, Q3, Rl, through R4, and C2. Q3 conducts for approximately 2 milliseconds and thereby discharges timing capacitor Cl via R6 and DI. Discharge of Cl removes the positive voltage from the emitter of Q5, and each of transistors Q6 through Q13 are 75 thereby rendered nonconductive. At the conclusion of the in3,629,480 terval during which Q3 is conductive, linear charging of Cl begins again by means of the constant collector current from Q2. Sequentially switching of Q6 through Q12 is repeated to provide a sequential primary pulses No. 1 through No. 7 at the collectors of respective transistors Q14 through Q20.

Pulses are applied to the base of respective NPN-transistors QS1 through Q63 inclusive. The emitters of these transistors are connected via respective emitter resistors RE1 through RE13, inclusive, to —50 volts DC, the bases being connected via respective base resistors RBI through RB13, inclusive, to +50 volts DC. In addition the bases of Q51 through Q63 are connected to the anodes of respective diodes D31 through D43, inclusive, the cathodes of which are connected to the collectors of different ones of transistors Q14 through Q20. More particularly, the collector of Q14, which provides primary pulse No. 1, is connected to the cathodes of D31 and D38. Likewise, primary pulse No. 2 is applied to the cathodes of D32 and D39, primary pulse No. 3 is applied to the cathodes of D33 and D40, primary pulse No. 4 is applied to the cathodes of D34 and D41, primary pulse No. 5 is applied only to the cathode of D35, primary pulse No. 6 is applied to the cathodes of D36 and D42, and primary pulse No. 7 is applied to the cathodes of D37 and D43. The collectors of Q51 through Q57, inclusive, are connected to secondary pulse control line 1, and the collectors of 058 through Q63, inclusive, are connected to secondary pulse control line 2. These control lines emanate from a circuit to be described in detail subsequently; however for present purposes it is to be understood that one or the other of these control lines, but not both, is at +28 volts DC while the other is at substantially ground potential.

In the absence of a positive-going primary pulse applied to its base diode, each of transistors Q51 through Q63 is biased off by the fact that its base junction is shunted to ground by its base diode connected in series with one of the normally conducting transistors Q14 through Q20. A positive-going primary pulse applied to the cathode of any one of the diodes D31 through D43 biases that diode off and thereby increase the voltage at the base of the associated transistor Q51 through Q63. If that transistor has+28 volts DC applied to its collector by the appropriate secondary pulse control line, that transistor is rendered conductive and a positive pulse, corresponding to the positive pulse applied to its base diode, appears across the emitter resistor of that transistor. The various signal lines numbered 1 through 13 and connected to the emitter electrodes of corresponding transistors Q51 through Q63 carry secondary pulses, or master timing pulses, to respective horizontal lines 1 through 13 of the rhythm selection matrix to be described in detail below in relation to FIGS. 3a and 3b.

Referring now to FIG. 2b there is illustrated a half-measure bistable circuit. The half-measure bistable circuit comprises four NPN-transistors Q21 through Q24, inclusive, interconnected by respective coupling resistors and capacitors to provide bistable operation. Output transistors 021 and Q24 are always of opposite states in accordance with the existing state of the half-measure bistable circuit. Secondary pulse control line 1, which as described above is connected to the collector electrodes of 051 through Q57, is derived from the emitter electrode of Q24. Secondary pulse control line 2, which as described above is connected to the collector electrodes of 058 through Q63, is derived from the emitter electrode of Q21. Trigger pulses are applied to the half-measure bistable circuit via capacitor C20 from the collector of Q3 each time the master timing ramp waveform is reset. Thus, for alternate cycles of the ramp waveform, the half-measure bistable circuit alternates states, and likewise secondary pulse control lines 1 and 2 alternate states. Thus, during one ramp cycle 051 through 057 are gated on by the master timing pulses, and during the next ramp cycle Q58 through Q63 are gated on by the primary timing pulses. In this manner, Q51 through Q63 are gated on sequentially over two ramp periods to provide 13 secondary or master timing pulses. The 13 master timing pulses constitute a musical measure, and consequently two timing ramp periods determine the duration of each measure.

The relative spacing between the master timing pulses is determined by resistors RSI and R20 through R33 associated with the emitter circuits of Q6 through 013. A particular set of values, indicated in the drawings, yield a preferred timing relationship between these pulses such as that illustrated in the top line of the timing diagram in FIG. 5. The 13 pulse measure is divided into 24 equal time units, with adjacent master timing pulses being separated by integral numbers of units. More particularly, each ramp period or half-measure (during which primary pulses No. 1 through No. 7 are generated) is divided into 12 equal timing units wherein primary pulses No. 1 and No. 2 are separated by three timing units, pulses No. 2 and No. 3 No. one timing unit, pulses No. 3 and No. 4 by two timing units, pulses No. 4 and No. 5 by two timing units, pulses No. 5 and No. 6 and pulses No. 6 and No. 7 by one timing unit each, and pulses No. 7 and No. 1 by two timing units. Since primary pulse No. 5 actuates a transistor only in alternate ramp periods, only six secondary or master timing pulses are generated in alternate half-cycles. Thus, the spacing between master timing pulses 8 and 7 is the same as the spacing between primary pulses No. 7 and No. 1, the spacing between master timing pulses 9 and 8 is the same as the spacing between the primary pulses No. 1 and No. 2, etc. The only difference between the secondary portion of each measure and the first portion thereof is the three timing unit spacing between pulses 11 and 12, due to the omission of primary pulse No. 5 in the second half of the measure. Two complete measures of master timing pulses are illustrated in FIG. 5 for reasons to be described in detail below.

As described above, the constant current delivered to timing capacitor Cl to generate the master timing ramp is determined by the setting of the center arm of the variable resistor Pl. The greater the current the shorter the period of time required for the ramp voltage to trigger each successive resistor Q6 through Q13 and recycle itself. Since the number of ramps generated per unit time can be controlled in this manner, the measure time, and hence the tempo of the accompaniment system, is controlled by means of Pl. Resistor RS2, in series with the emitter of Q2 and the center arm of Pl, is preferably selected to provide a tempo of two measures per second when the center arm of Pl is set to the minimum resistance or “fast” tempo position.

Because of the wide component tolerance spread effecting the time interval between the primary pulses No. 7 and No. 1, it is necessary to select resistor RSI in the emitter circuit of Q6 such that the time between primary pulses No. 7 and No. 1 is as desired. As illustrated in the master timing pulse timing diagram, FIG. 5, RSI is selected to provide a two timing unit spacing between pulses No. 7 and No. 1, which is the same spacing as between primary pulses No. 4 and No. 5.

Each time transistor Q24 in the half-measure of bistable circuit is rendered conductive, signifying the start of a measure, a pulse is applied via coupling capacitor Cll and resistors R63 and R64 to the base of a transistor Q25. The collector-emitter circuit of transistor Q25 is connected in series with an indicator lamp LI and resistor R91 between +28 volts DC and ground. When pulsed, NPN-transistor Q25 turns on, providing a current path by which lamp LI may be lit. Capacitor C17 is connected across lamp LI to ground to maintain the lamp lit for a period of about 100 milliseconds at each downbeat or first master timing pulse in each measure.

It is sometimes desireable to have a rhythm accompaniment of two measure duration; that is the rhythm pattern in alternate measures is somewhat different. The control circuitry for achieving this is illustrated in the FIG. 2b and includes an alternate bistable circuit comprising NPN-transistors, Q32 and Q33 interconnected by various resistors and capacitors to provide conventional bistable operation. A “B” control signal is provided from the collector of Q33 and a “C” control signal is provided from the collector of Q32. Depending upon the state of the alternate bistable circuit, one of the B and C control signals is at +16 volts DC while the other is at substantially ground. Trigger signals are applied to the alternate bistable circuit via coupling capacitor C14 from the arm of a toggle

3,629,480 switch S2. When S2 is in its alternate position, each pulse through downbeat lamp LI is conducted through S2 and C14 to trigger the alternate bistable circuit. In this mode the alternate bistable circuit is switched by the first timing pulse of each measure and has a switching frequency which is half that of the half-measure bistable circuit. Alternatively, with switch S2 in its random position, a trigger is applied to the alternate bistable circuit via capacitor C14 from a random oscillator circuit comprising NPN-transistors Q34, 035, and Q36. More particularly, transistors Q34 and 035 are interconnected by appropriate resistors R84, R85, and R86 and capacitor C16 provides an oscillatory signal at the emitter of Q35 which signal has a low frequency on the order of 5 Hz. This signal is applied via resistor R87 to the base of Q36 which has its collector emitter circuit connected in series with the resistor R88 between +22 volts DC and ground. The collector of Q36 thus provides a train of positive-going pulses of approximately 50 millisecond pulse width and approximately 200 milliseconds period. These pulses, with S2 in the random position, trigger the alternate bistable circuit at the 5 Hz. rate, which is random relative to the frequency of the ramp timing signal. For either position of S2, the B and C control signals alternate state and, in a manner to be described in relation to FIGS. 3α and 3b below, determine the rhythmic pattern to be produced during 25 each measure.

Also illustrated in FIG. 2b is a stop/start bistable circuit comprising NPN-transistors Q29 and Q30 interconnected by appropriate resistors and capacitors to operate in bistable fashion. It is the state of this bistable circuit which influences the condition of transistor 031 such that in one state of the stop/start bistable circuit Q31 is conductive to shunt the collectors of Q14 through Q20 of FIG. 2α to ground via diodes D5 through Dll, thereby inhibiting the primary timing pulses. In the other state of the stop/start bistable circuit, transistor 031 is nonconductive, conduction through diodes D5 through Dll is blocked, and the master timing pulses are sequentially generated. Stop/start switch S3, a normally open grounding switch, when actuated changes the state of the stop/start bistable circuit via triggering capacitor C13 and a bounce suppression network including resistors R70 and R71, diode D20 and capacitor C19.

A one-shot multivibrator, including NPN-transistors 026 and Q27 and PNP-transistor Q28 has the function of resetting the timing ramp to its start condition whenever the system is started, as by actuation of switch S3. The base of Q26 is connected to the collector of Q29 in the stop/start bistable circuit and its collector is connected to +28 volts DC. The emitter of 026 is connected to ground via resistor R65 and is coupled to the base of Q27 via capacitor Cl 2 and resistor R66. The junction between capacitor C12 and resistor R66 is connected to the cathode of clamping diode D14, the anode of which is connected to ground. The base of Q27 is connected to -50 volts DC via resistor R67. The collector of Q27 is connected to +28 volts DC via resistor R68 and to the junction between resistor R6 and diode DI via diode D2, poled for conduction through the collector-emitter circuit of Q27. The emitter of Q27 is tied directly to the emitter of Q28 and, via resistor R69, to the collector of Q28. The base of Q28 is connected to the emitter of transistor 06, in FIG. 2α, 06 being the first to trigger during each ramp period.

The system is started when transistor Q29 turns off. At this time Q27 is turned on for nominally 6 milliseconds under the 55 influence of capacitor C12 and resistor R66 via buffer Q26. The drop across C12 necessary to provide the correct transient time for Q27 is achieved by clamping diode D14 which quiescently (i.e. when Q27 is off) clamps one-side of C12 substantially to ground potential. When Q27 is conduc- 70 tive, timing capacitor Cl is discharged via R6, D2, and the collector emitter circuits of transistors 027 and Q28. This effectively turns off Q6 and assures, for all practical purposes, that the ramp waveform and timing pulses produced therefrom are recycled when the system is started.

To assure that the system starts in the first half of each measure, the positive transient voltage appearing at the junction of C12 and R66 when Q29 turns off is employed via resistors R90 and R62 to trigger the alternate bistable and half-measure 5 bistable circuits respectively. This assures that the B control signal, at the alternate bistable circuit, and secondary pulse control line 1, at the half-measure bistable circuit, are rendered positive when the system starts.

Stop/start switch S3 is described above as being effective to stop or start the automatic rhythm accompaniment tones of the present invention. S3 is preferably a foot switch which when employed to stop the accompaniment effectively shunts the timing pulses to ground via diode D5 through Dll as described. Note however that the timing circuit is still operative in the sense that the master timing ramp sequentially actuates Q6 through Q13. In order to completely disable the master timing circuit, switch SI, which is ganged to variable resistor Pl, is opened to thereby apply —50 volts DC to the 2θ collectors of 04 and Q5 via resistor R93. This effectively cuts off Q4 and Q5 and prevents application of the ramp voltage to Q6 and through Q13. Since 013 is prevented from triggering QI and Q3, timing capacitor Cl cannot discharge and the repetitive ramp pattern is terminated. Opening of SI also drives the collector of transistor Q29 of the stop/start bistable circuit negative via diode D19 and resistor R93 so that Q29 is maintained off. If SI is now closed, Q4 and Q5 are enabled and current flows into Cl to reinitiate the repetitive ramp waveform.

Resistor R72 connected between the base of the emitter of Q30 in the stop/start bistable circuit serves as a bias during turn on of the system power supply such that the system settles in a condition whereby Q31 is conductive to inhibit the primary timing pulses from Q14 through Q20.

There is also provided in FIG. 2b a roll oscillator comprising NPN-transistors Q39 and Q40 interconnected by appropriate resistors and capacitors to provide an oscillatory output signal at a frequency of approximately 25 Hz. This signal, taken from the collector of Q40, is applied to the base of PNP-transistor

041, the emitter of which is connected to +28 volts DC and the collector of which is connected to a common junction from which the brush roll control signal (via resistor R80 and diode D14) and snare roll control signal (via resistor R81 and diode D15) are provided, these signals being positive pulses at 45 the 25 Hz. rate if Q41 is not inhibited. Said common junction is coupled via diode D18 to the collector of NPN-transistor 037 which, along with NPN-transistor Q38 and appropriate resistive and capacitive interconnecting circuitry, comprises a roll control bistable circuit. In one state of the roll control bistable circuit Q37 is conductive to ground, effectively shorting out the brush and snare roll control signals. In the opposite state of the roll control bistable circuit Q38 is conductive and 037 is not, thereby rendering the brush and snare roll control 55 signal operative to effect the appropriate simulated drum rolls as described hereinbelow. The state of the roll control bistable circuit is determined by the roll start signal applied to the base of 038 and the roll finish signal applied to the base of Q37, both of which signals are received from the rhythm selection matrix described in detail in reference to FIGS. 3α and 3b. The roll start signal triggers Q38 on and Q37 off to enable the brush and snare roll control signals; the roll finish signal triggers 037 on to inhibit the brush and snare roll control signals.

Before describing the rhythm selection matrix, brief mention should be made of the shush 1 and shush 2 signals. Shown is a term which refers to the background noise appropriate to some rhythm accompaniments. Shush 1 is a consistent noise level realized by connecting R7 to a suitable voice circuit in the manner described hereinbelow with reference to FIGS. 4α and 4ft. Shush 2 refers to a noise character which decreases through the beginning portion of the measure until reaching a consistent level at the middle of the measure, which level is retained until the measure is completed. This is realized by mixing a steady noise signal, set up by R8, and a noise signal 75 having a triangular envelope during the first half of the mea3,629,480 sure, and employing only a steady level during the second half of the measure. More particularly, the triangular envelope is generated from the master timing ramp during a first ramp cycle via resistor R9 connected to the emitter of QS. During the next ramp cycle secondary pulse control signal 2, provided by the emitter of Q21, is supplied by diode D4 to override the ramp signal and provide a steady level for the shush 2 signal.

Referring now to FIGS. 3a and 3b of the accompanying drawings, there is illustrated a resistive matrix in which the horizontal lines are 13 in number, corresponding to the 13 master timing pulses which are applied thereto and which are illustrated in the top line of each measure in FIG. 5. A total of 47 vertical matrix lines are illustrated, the vertical lines being divided into eight groups representing different rhythms. The number of rhythm groups illustrated is by way of example only and not to be considered limiting on the scope of the present invention. Vertical lines and horizontal lines are selectively interconnected at appropriate junctions by 100 K resistors so that a signal is provided on each vertical line in time coincidence with a pulse on a horizontal line to which that vertical line is resistively coupled. Thus, for example, vertical line 1 is seen to be resistively coupled to horizontal lines 1, 4, 7, 8, 11 and 13, indicating that during each measure the 1,4, 7, 8, 11, and 13 master timing pulses appear on vertical line 1. Likewise vertical line 29 is resistively coupled to the 4 and 8 master timing pulse lines to thereby provide the 4 and 8 master timing pulses during each measure.

The groups into which the vertical lines are divided are as follows:

<td> Line Numbers</td><td> Rhythm</td>

<td> 1-5</td><td> SWING</td>

<td> 6-1!</td><td> BALLAD</td>

<td> 12-17</td><td> ROCK</td>

<td> 18-20</td><td> WALTZ</td>

<td> 21-26</td><td> BOSSA NOVA</td>

<td> 27-34</td><td> RHUMBA</td>

<td> 35-42</td><td> LA TIN III</td>

<td> 43-47</td><td> MARCH</td>

5, 17, 26, and 47 of the rhythm selection matrix. The snap trigger line is a combination of the Snap A, Snap B, Snap C signals. (“Snap,” used herein interchangeably with Brush, refers to the sound produced by striking a brush stick on a 5 drum or the operation of a Hi-Hat.) The snap A signal is connected directly to the Snap trigger line and receives pulses from vertical lines 6, 12, 18, 21, 27 and 35 of the matrix. The Snap B signal is selectively gated to the Snap trigger line by means of series diode 87 and shunt diode 86, the cathode of ^u the latter being connected to the B control signal provided by the alternate bistable circuit in FIG. 2b. When the B control signal is positive, diode D86 is blocked and the Snap B signal is conducted through diode D87 to the Snap trigger line. When ! ₅ the B control signal is grounded diode D86 shunts pulses appearing on the Snap B line to ground and inhibits their application to the Snap trigger line. The Snap B signal is derived from vertical line number 1 of the matrix.

A Snap C signal is applied selectively to the snap trigger line 2q via a diode gate comprising series diode D89 and shunt diode D88, the cathode of the latter being connected to the C control signal provided by the alternate bistable circuit of FIG. 2b. When the C control signal is positive D88 is blocked and the pulses appearing on the Snap C line are connected to the Snap 25 digger line. When the C control signal is grounded D88 acts to shunt all Snap C signals to ground and prevent their conduction to the Snap trigger line. Thus, depending upon the state of the alternate bistable circuit of FIG. 2b, either the pulses appearing on the Snap B line or those appearing on the Snap C 30 line are conducted to the snap voice circuit via the Snap trigger line during any given measure. The Snap A pulses, however, are conducted to the Snap voice circuit during every measure, irrespective of the state of the alternate bistable circuit.

In like manner, there are provided, by means of various combinations of the vertical lines in the matrix, Snare A, Snare B, Snare C, Bass A, Bass B, Bass C, Clave B, Clave C, Cowbell A, Cowbell B, Cowbell C, Conga A, Conga B, and Conga C signal lines, which apply pulses to their respective voice circuits. All of the pulses appearing on a B trigger line are gated through to their respective voice circuits only when the B control signal from the alternate bistable circuit is positive. Likewise, all of the pulses appearing on a C trigger line are gated through to their respective voice circuits only during measures in which the C control signal provided by the alternate bistable circuit is positive. The signals are applied to their respective voice circuits during every measure.

In addition, vertical lines 10 and 44 of the matrix are combined to provide the roll start signal, which is applied to the base of Q38 in the roll control bistable circuit of FIG. 2b. Likewise, vertical lines 11 and 45 are combined to provide the roll finish signal, applied to the base of Q37 in the roll control bistable circuit. The brush and snare roll control signals provided at the collector of Q41 are connected to the Snap A and Snare A lines respectively to provide a repetitive positive voltage to these signal lines, and thereby to their corresponding voice circuits, whenever a roll is to be simulated.

Each of the sWING, BALLAD, and WALTZ automatic 60 rhythm switches have an extra pole ganged thereto for purposes of providing shush effects. More particularly, the shush 1 signal is applied to the second pole of the SWING switch which, when actuated, applies to the shush 1 signal to the Cymbal voice circuit, to be described below in reference to 65 FIGS. 4α and 4b. The second pole of the BALLAD and WALTZ automatic rhythm switches selectively apply the shush 2 signal to the Cymbal voice circuit.

Operation of the matrix of FIGS. 3α and 3b may best be illustrated with reference to the timing diagram of FIG. 5. Using 70 as an example the SWING rhythm, for which we assume that the SWING automatic rhythm switch has been actuated, the Bass A signal is pulsed by the first, fourth, eighth, and 1 1th master timing pulse during each measure, these pulses being equally spaced (by six timing units) to provide the standard 75 four beats to the measure required for the SWING rhythm.

The LATIN III rhythm can represent the cha-cha, mambo, or samba according to the tempo selected by variable resistor P1. The other rhythms are self evident. 45

Each vertical line 1-47 is connected to the anode of a respective diode D14 through D60, respectively. The cathodes of D14 through D18, in the SWING rhythm group, are connected to one pole of a two-pole SWING switch which, when not actuated effectively grounds the cathodes of these diodes and thereby shunts positive pulses appearing on vertical lines 1-5 to ground. When actuated the SWING switch leaves the cathodes of D14 through D18 floating, thereby enabling vertical lines 1-5 to conduct their resistively coupled master timing pulses further along the circuit. Likewise, the diodes associated with the BALLAD lines 6 through 11 are shorted to ground by one pole of the BALLAD switch unless the latter is actuated. Similar selective shorting of the vertical lines in the ROCK, WALTZ, BOSSA NOVA, RHUMBA, LATIN II, and MARCH groups is accomplished by respective automatic rhythm switches. Thus by actuating the appropriate automatic rhythm switch a group of vertical lines corresponding to the selected rhythm are enabled.

The sequential pulses appearing on the vertical lines are connected to various appropriate voice circuits of FIGS. 4α and 4b, described in detail hereinbelow. The voice circuits respond to application of positive trigger pulses thereto to produce rhythmic sounds which simulate those produced by musical accompaniment instruments. Thus, and the inclusion of the following circuits is by no means limiting, there are provided the following voice circuits connected to respond to the triggers produced by the matrix of FIGS. 3α and 3b: Cymbal, Snap, Snare, Bass Drum, Clave, Cowbell, and Conga Drum. The Cymbal trigger line is resistively coupled to vertical lines

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The Snap trigger line is pulsed by the Snap B signal during B measures at the first, fourth, seventh, eighth, 11th and 13th master timing pulses, and by the Snap C signal during C measures at the first, fourth, eighth, 10th, 11th and 13th master timing pulses. Thus, when the alternate bistable circuit of FIG. 5 2b operates in its alternate mode, during alternate measures, the Snap voice circuit is triggered by different pulse patterns in each measure. Also for the SWING rhythm it is seen that the Bass C signal pulses the base voice circuit during C measures at the seventh master timing pulse to provide an effec- 10 tive prebeat (by the Bass Drum) before the third pulse of alternate measures. In addition, the Cymbal voice circuit is triggered by the fourth and 11th master timing pulse of each measure.

To illustrate the effects of the roll control circuits, reference ' 5 is made to the BALLAD rhythm mode wherein master timing pulse 1 appears on vertical line 10 of the matrix to provide a roll start pulse at the start of each measure. The roll start pulse turns off Q37 at the roll control bistable circuit of FIG. 2b to thereby enable the brush and snare roll control signals. The ²⁰snare roll control has no effect at this time since it is connected to D56 and thereby shunted to ground via the MARCH automatic rhythm switch. However the brush roll control signal is applied to vertical line 6 to provide a Snap A signal. This signal keeps the Snap A line pulsed at 25 cps. for as long as the brush roll control signal is present. This condition obtains until the occurrence of pulse four, at which time the roll finish pulse is generated via vertical line 11 of the matrix to turn on transistor Q37 in the roll control bistable circuit. This inhibits the brush roll control signal which is thereby removed from the Snap A trigger line. The positive voltage appearing on the Snap trigger line during the interval between pulses 1 and 4 of each measure cause the Snap voice circuit to produce a characteristic brush roll sound over that interval during each measure.

The particular choice of 24 basic timing units in each measure permit accurate and realistic rhythmic patterns to be produced by the present system. More particularly, since 24 is readily divisible by two, three, four, 6, six, eight and 12, a ₄₀larger variety of basic rhythms are readily reproducible. For example, 4 beats to a measure, as required by the BALLAD, SWING, etc., is readily provided by simply utilizing pulses 1, 4, 8, and 11 in each measure, these pulses being separated by six timing units each. Three beats per measure, as required by 45 the WALTZ, is readily achieved by means of pulses 1, 5, and 10, separated by 8 timing units each, in each measure. A faster waltz, though not provided for expressly by the circuitry illustrated and described herein, can likewise be reproduced by utilizing pulses 1, 3, 5, 8, 10 and an additional master timing 50 pulse between pulses 11 and 12, spaced two timing units from pulse 11. The variety of selectable rhythms is thus substantially unlimited by virtue of the particular timing arrangement selected.

The system as described heretofore is adapted to be built 55 into a musical instrument such as an electronic organ, and as such must be adapted to permit manual keying of the various voice circuits when automatic rhythm accompaniment is either not desired, or of itself is not sufficient to produce the desired effects. To this extent, each of the voice circuits may 60 be triggered via specially provided manual rhythm switches (FIG. 4α) such as the bass pedal, brush pedal, clave pedal, cymbal pedal, brush accompaniment, snare accompaniment, conga accompaniment, and cowbell accompaniment switches. The pedal switches receive a pedal trigger generated in a 65 manner described hereinbelow and, when actuated, apply this trigger to the corresponding voice circuits of FIGS. 4α and 4b. The accompaniment switches are operative to apply accompaniment triggers, generated in the manner described hereinbelow, to corresponding voice circuits. These manual rhythm 70 switches are operative in conjunction with an on/off button which; in the off position, shunts the accompaniment and pedal trigger signals to ground and which, in the on position, permits application of these trigger signals to the appropriate voice circuits. 75

Referring still to FIGS. 4a and 4b there is illustrated an accompaniment trigger amplifier comprising transistors Q20 and Q21 connected in monostable multivibrator configuration. Actuation of appropriate keys at the keyboard of the electronic organ provides a signal to the accompaniment input terminal which triggers the monostable circuit to provide an accompaniment trigger pulse to four of the manual rhythm switches. The accompaniment trigger pulse is approximately +22 volts in amplitude and has, nominally, a 5 millisecond duration. Likewise a pedal trigger amplifier is illustrated and is similar to the accompaniment trigger amplifier except that two mutually exclusive input circuits are provided. One of these is used in conjunction with the monophonic pedal latch system and the other with a polyphonic system. When triggered, the pedal trigger amplifier, comprising a one-shot multivibrator including transistors Q22 and Q23, provides an output pulse of the same general character as the accompaniment trigger. The pedal trigger is also applied to four of the manual rhythm switches as described above.

The cymbal, snap (brush) share drum, bass drum, clave and conga drum voice circuits are conventional in nature, each responding to an input trigger applied thereto for providing a percussive tone simulating the sound signified by the name of the voice circuit. For example, the clave sound simulates two hard wooden rods struck together. A trigger received at the base of transistor Q12 of the clave circuit gates Q12 on for the duration of the trigger pulse. This renders Q13 conductive and gates on the gated oscillator configuration including transistor Q13 to provide a sinusoidal signal of decaying amplitude and of such frequency to simulate the clave sound. The decay period is determined by resistor R34 and capacitor C23 connected in series between the emitter of Q13 and ground. Similar operation ensues in each of the cymbal, snap, snare drum, bass drum, and conga drum circuits, wherein gated oscillator of approximate frequency is triggered on by a transistor switch in response to each applied voice trigger pulse. The oscillator amplitude then decays upon removal of the trigger pulse. The triggers received by each of the conga drum, clave bass drum, cymbal and snare drum voice circuit are the appropriate automatic triggers supplied by the matrix of FIGS. 3α and 3b, or by the accompaniment or pedal triggers supplied by the manual rhythm switches in FIG. 4α. The Snap voice circuit receives three triggers, namely the brush accompaniment and the brush pedal trigger, as well as the automatic trigger provided by the matrix. The brush or snap voice circuit may thus be triggered manually by either pedal or key actuation.

A novel voice circuit included in FIG. 4b is the cowbell voice circuit which, when triggered, provides a combined 1 kHz. and 2 kHz. decaying tone, the frequency of the 2 kHz. signal being prevented from shifting during the decay of the tone. The cowbell circuit includes a gated 1 kHz. oscillator comprising NPN-transistor transistor Q17 and associated resistors and capacitors connected to produce the 1 kHz. oscillatory signal at the emitter of Q17 whenever gating transistor Q18 is triggered on by an input trigger. To this extent, the 1 kHz. signal is actuated as in the other voice circuits. Thus, when triggered, Q18 remains on for the duration of the trigger pulse, gating on the 1 kHz. oscillator via resistor R52 and diode D3. Upon termination of the trigger pulse, Q18 turns off but the 1 kHz. signal is sustained at a decaying amplitude over a sustan period determined by capacitor C36 and resistor R52. The gated decaying 1 kHz. signal is applied to a common voice circuit output line via resistor R65 and capacitor C44.

The 2 kHz. oscillator in the cowbell voice circuit comprises NPN-transistor Q16 and associated resistive and capacitive elements interconnected to provide a continuously running 2 Hz. oscillator. The 2 kHz. signal is applied via capacitor C58 to a linear gate which includes diodes D4 and D5, capacitor C38, and resistors R56 and R57. When conductive, the linear gate applies the continuous 2 kHz. signal to the common voice circuit output line via resistor R66 and capacitor C45. When Q18 is gated on by an input trigger pulse, PNP-transistor Q19 experiences a reduction in base voltage which renders it con3,629,480 ductive. This supplies gating current via resistor R55 to the linear gate, turning the latter on and permitting passage therethrough of the 2 kHz. signal. Conduction of current through Q19 also charges capacitors C37. When the input trigger applied to the base of Q18 terminates, the latter turns off and in turn renders Q19 nonconductive. The linear gate remains on due to the charge existing on capacitor C37, which now discharges through two resistive paths, one of which includes R57, D4 and R58, the other of which includes R56, D5 and R59. The amplitude of the 2 kHz. signal applied through the linear gate to the common output line decreases as C37 discharges until eventually the linear gate is cut off and the 2 kHz. tone terminates. Importantly, the linear gate (linear in the sense that no distortion of the 2 kHz. signal is produced when passed therethrough) is required to prevent frequency shift of the 2 kHz. signal, which shift would alter the character of the cowbell tone to produce something which is not realistic.

the output signals from all of the voice circuits are tied to a common output line which is connected to the center arm of the volume control, a variable resistor connected between the input terminal to the pedal preamplifier and ground.

Generation of the shush 1 and shush 2 signal proceeds when appropriate ones of the automatic rhythm switches are actuated as described in relation to FIG. 3b. More particularly the shush output line from the automatic rhythm switches is connected to the cathode of diode D2, the anode of which is connected to transistor Q6 in the cymbal voice circuit. When an appropriate automatic rhythm switch is closed, the common shush line, in combination with the actuated switch and either of the shush 1 or shush 2 lines, provide a path for emitter current through diode D2 for transistor Q6. The latter conducts to feed suitable signal via the cymbal voice circuit (based on transistor Q9) to provide cymballike noise at the system output unit for as long as the shush 1 or shush 2 signals are selected by the automatic rhythm switches. Note that the shush signals are not derived from rhythmic pulses gated through the rhythm selection matrix but rather are continuous sounds generated throughout each measure. A shush inhibit signal applied to diode DI in FIG. 4α from the collector of transistor Q30 in stop/start bistable circuit of FIG. 2b prevents generation of a shush signal when the automatic rhythm system is off. More particularly, when the system is off, transistor Q30 in the stop/start bistable circuit is nonconductive rendering the shush inhibit signal positive. This biases diode DI on at the cymbal voice circuit and applies a positive voltage to the cathode of diode D2, which voltage is greater than the quiescent voltage at the base of transistor Q6. This prevents transistor Q6 from conducting as long as the shush inhibit is positive; therefore no shush signals can be generated at this time.

Referring now to FIG. 6 of the accompanying drawings there is illustrated an alternative approach to generating the master timing pulses in the system of the present invention. In the above-described embodiment there are two ramp signals generated for each measure, which results in the generation of seven primary pulses. These pulses are appropriately gated during alternate half-measures to produce 13 master timing pulses per measure. In the circuit of FIG. 6 the approach is to generate one linear ramp per measure, which ramp triggers all 13 master timing pulses directly, in the same manner as the seven primary pulses are triggered in the FIG. 2α. More particularly, the circuit of FIG. 6 includes a constant current source based on transistor QI02 which is directly analogous to the constant current source which includes transistor Q2 of FIG. 2α. Likewise, the reset monostable circuit for the ramp generator includes transistor Q101 and Q103, analogous to transistors QI and Q3 of FIG. 2α. Also provided is an emitter follower buffer circuit including transistors Q104 and Q105, analogous to transistors Q4 and Q5 of FIG. 2α. The values of the various resistors and capacitors associated with transistors 0101 through Q105 differ from the values of the components employed with transistors QI through Q5 of FIG. 2α, primarily ' because of the nature of the ramp generated in FIG. 6 which ramp must have a duration of twice that of the ramp of FIG. 2α. The emitter of Q105 is coupled in parallel to the base of each of 14 transistors QI 11 through QI24. These latter transistors are normally nonconducting and are triggered into conduction at respective increasing voltage levels of the linear ramp signal appearing at the emitter of Q105. Transistor Q124, which is driven into conduction last of all transistors QI 11 through Q124 during each ramp period resets the ramp signal by triggering the reset monostable circuit comprising Q101 andQ103. As each ofQlll through Q123 is driven into conduction a trigger pulse is AC coupled to a respective one of pulse generators 111 through 123, all of which are identical, only generator 123 being illustrated in detail. Each of the pulse generators includes a pair of NPN-transistors QI25 and Q126 connected in cascade, with the input trigger being applied to the base of QI25 and the output signal taken from the emitter of Q126. Q125 is normally conducting and Q126 is normally nonconducting. When transistor Q123, for example, is driven into conduction by the input ramp, a negative going transition appears at the collector of Q123 which is coupled via an input coupling capacitor to the base of Q125 to turn the latter off. Voltage at the collector of Q125, and hence at the base of Q126, increases, rendering Q126 conductive to provide a positive-going pulse at the emitter electrode of Q126. This pulse is the master timing pulse provided by the pulse generator.

The 13 master timing pulses produced by pulse generators ill through 123 are preferably spaced, as determined by the emitter biases for transistors Qlll through Q124, in the manner illustrated in the top line of the timing diagram of FIG. 5. As described, this particular spacing permits generation of authentic rhythm patterns not previously attainable in prior art rhythm systems. While other techniques for generating desired master timing pulse patterns may be employed in the scope of the present invention, those techniques described in relation to FIGS. 2α and 6 are believed the simplest and the most easily effected.

Referring now to FIG. 7 of the accompanying drawings there is illustrated an alternative approach to providing a rhythm selection matrix for performing the same function as the matrix illustrated in FIGS. 3α and 3b. More particularly, the 13 input timing pulses are applied to horizontal lines of the matrix just as in FIGS. 3α and 3b, and the vertical lines of the matrix are selectively resistively coupled with the various horizontal lines and grouped in accordance with the particular selected tempos. Whereas selection of the tempo in FIGS. 3α and 3b is achieved by ungrounding respective groups of diodes D14 through D61 by means of the automatic rhythm switches, in FIG. 7 the shunt diodes are eliminated and replaced by respective series sections of each automatic rhythm switch. Thus actuation of the SWING automatic switch closes 5 switches in series with vertical lines 1 through 5 to enable the selected master timing pulses resistively coupled to these lines to be applied to the various voice circuit trigger lines.

It is to be stressed at this point that although the trigger patterns generated for each rhythm in FIGS. 3α and 3b are identical to the patterns selected in the circuit of FIG. 7, the particular patterns illustrated in FIG. 5 are not limiting as to the scope of the present invention. For example, it may be desirable to additionally generate a Snap A pattern for the SWING rhythm or eliminate the Snap C pattern in that rhythm. Numerous combinations are of course applicable to produce other desired rhythmic effects. The patterns illustrated in conjunction with the matrices in FIG. 3b and 3α and FIG. 7 and in the timing diagram of FIG. 5 are believed to be most authentic in so far as simulation of standard rhythm patterns are concerned. Likewise, additional rhythm patterns other than the eight illustrated in conjunction with FIGS. 5 and 3α and 3b may be provided by the techniques disclosed, their authenticity in simulating actual standard rhythm patterns being facilitated by the particular choice of master timing pulse spacing provided herein.

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Referring now to FIG. 8 of the accompanying drawings there is illustrated a modified control circuit for providing greater flexibility in selecting measure patterns than is possible in the embodiment disclosed above. More particularly, there is illustrated in FIG. 8 the alternate bistable circuit, substantially identical to that illustrated in FIG. 2b, having a control switch S2 identical to that in FIG. 2b from which the state of the alternate bistable circuit may be controlled, either by the random oscillator or the downbeat signal as described in relation to FIG. 2b. In addition there is provided a switch S6 schematically illustrated as having three positions, namely an off position, a B position, and a C position. In the B position switch S6 grounds the collector of Q32 of the alternate bistable circuit and in the C position grounds the collector of Q33. If the collector of Q32 is grounded the collector of Q33 is at a positive voltage and the B pattern is continuously produced by the matrix as long as S6 is in this position. When S6 grounds the collector of Q33, in a similar manner, the C pattern is continuously produced. The addition of switch S6 therefore provides four different pattern modes, each capable of selection by the performer. These modes are:

1. with S6 in the B position, regardless of the position of S2, the B pattern is continuously produced during each measure;

2. with S6 in the C position, the C pattern is continuously produced, regardless of the position of S2, during each measure;

3. with S6 in the off position and S2 in the alternate position patterns B and C alternate during successive measures;

4. with S6 in the off position and S2 in the random position, patterns B and C are switched at a random rate relative to the repetition rate of the measures in accordance with the random triggering from the random oscillator, thereby producing a continuously varying rhythm pattern.

Thus two different single measure patterns may be produced or alternated or randomly selected in accordance with the settings at S2 and S6.

The B control and C control signals provided at respective collectors of transistors Q33 and Q32 may be employed as illustrated in FIGS. 3b to gate the various trigger lines at the output of the matrix. Alternatively these signals may be employed directly at the iriput circuits of each of the voice circuits of FIGS. 4α and 4h, as illustrated in FIG. 8. By way of example, the Snap voice circuit illustrated in FIG. 8 and the Snap B and Snap C trigger lines are illustrated as being connected to the anode of respective diodes D101 and D102, the cathodes of which are connected to respective collectors of transistors Q33 and Q32. When the B control signal is high and the C control signal grounded, diode D101 is blocked and Snap B pulses are applied directly to the Snap voice circuit; diode D102 is grounded and thereby shunts the Snap C triggers to ground. Alternately, when the C control voltage is high, diode D102 is blocked permitting application of Snap C triggers to the Snap voice circuit; D101 shunts the Snap B triggers to ground.

While I have described and illustrated specific embodiments of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.