Patent GB-984589-A (GB)
Title: Tempo control for electrical musical instruments
IPC: G10H1/40
Filed: 1963-07-29
Abstract: 984, 589. Electrophonic musical instruments. SEEBURG CORPORATION. July 29, 1963 [Aug. 1, 1962], No. 29951/63. Heading G5J. [Also in Division H3] An electrical music generating system of the type which includes a principal instrument e.g. an electrical organ, having a pulse tone source under player operation and a background instrument of the repetitive rhythm type having a pulse tone source under automatic operation, comprises electrical comparison means connected to be fed pulses from both instruments and adapted to compare the rates of pulsing therein, and electrical drive means connected between said comparison means and the pulse source of said background instrument and adapted to adjust automatically the rate of pulsing in said background instrument source in accordance with the output of said comparison means. As shown, Fig. 1 illustrates broadly the invention in which the pulse source 10 of the principal instrument, which is in time with the tempo at which the principal instrument is played, is fed to pulse comparison circuitry 11 which also receives pulses from the background instrument pulse source 12, e.g. drum pulse source, which is in time with the tempo of the background instrument. The pulse comparison circuitry 11 acts to compare the two pulse sources and produce an output whose effect is to control the drive source circuitry 13 from which the background instrument drive 14 is fed. Drive 14 which is a frequency sensitive device such as a synchronous motor controls the rate at which pulses are emitted by the background instrument pulse source 12. When pulses from the principal instrument pulse source 10 are synchronized with the pulses from the background instrument source 12, the drive 14 will remain at the speed at which it is running. If the pulses are not synchronized, the drive 14 automatically is made to speed up or slow down as required to bring the pulses in synchronization with the pulse rate of the principal instrument pulse source. Figs. 2 and 5 (not shown) are respectively a detailed block diagram and an electrical circuit diagram of an embodiment of the invention. The principal instrument pulses are precisely shaped as pulses and control an "AND" gate through which the background instrument pulses pass in the form of waves having been converted by means of an amplifier, differentiator, integrator, inverter and a differentiator-coupling from their spike form (Fig. 6, not shown) to a continuous wave form in which the ends of each respective wave coincides with the beginning of the next pulse. The electrical "comparison" takes the form of coincidence of arrival at the gate of the pulses and the waves (Fig. 7, not shown). Such wave portions as are passed by the gate are directed to a D.C. level memory circuit the output level of which controls the speed of the drive which produces the background instrument pulses i.e. the rate of pulsing in the background instrument pulse source. A difference in tempo between the two instruments results in a change in memory output level which changes the background instrument drive to make the tempos equal. The principal instrument pulses which are representative of the principal instrument tempo are derived by means of foot pedal operated switch (Fig. 3 not shown) and a pulse voltage supply and the rate at which pulses are derived from the pulse voltage supply depends on the rate at which the foot pedal is operated. Voltage and current control signals may be used directly to control the device which generates the repetitive rhythm pulse rate.