Patent GB-1435363-A (GB)
Title: Electronic musical instruments
IPC: G10H5/00
Filed: 1973-05-23
Abstract: 1435363 Electrophonic keyboard instrument CHICAGO MUSCIAL INSTRUMENT CO 23 May 1973 [12 Jan 1973] 24707/73 Heading G5J Multipole key switches in an electronic keyboard instrument are eliminated by cyclically scanning simultaneously the single pole key switches of upper and lower manuals of 61 keys each and pedal board of 32 keys, the three emergent pulse trains indicating by the presence of pulses at specific times in the cycle those keys pressed. Each successive pulse space represents one semitone rise, additional notes in harmonic relationship to those keyed being inserted by adding pulses delayed by fixed numbers of steps. Each pulse amplitude controls the intensity of the corresponding signal taken from a bank of tone generators during the following scanning cycle, subject to modification in optional percussive waveform circuits. The outgoing signals are finally modified by voicing filters. A multivibrator and divider circuit in scanner 16 produces a clock cycle of 128 pulses, the first being used to reset other units driven by the same clock pulses. Pulses 2-62 are passed to the 61 key switches 10 in turn and simultaneously to similar key switches 12; pulses 2- 33 are also passed to the 32 key switches 14. After adjustment of pulse level in 24, 30, 34, pulses are routed as required by data distribution unit 28 so that those from any keyboards may be passed to any of the coupler control units 42-45. In each such a separate shift register driven and reset by scanner 16 adds pulses delayed by harmonically desirable or other numbers of steps. For those pulses present, either original or delayed, gate circuits produce an output pulse with amplitude corresponding to the highest of various preset or external control voltages, e.g. supplied from amplitude control unit 46. Original pulses, together with pulses delayed from 1 to 60 steps (5 octaves up) may be present though not necessarily usable by later circuits. After amplification 58-61 the pulse trains from coupler control units 42- 45 enter sample and hold units 62-65, of which there are 61 in each of blocks 62, 63, and 32 in block 64, controlling signals drawn from tone generators 72, and a further 97 sample and hold units in block 65 controlling flute tone generators 86; notes over 5 octaves can be drawn from generators 72 of unspecified waveform, and 8 octaves from flute tone generator 86. Sample and hold units in different blocks but corresponding to the same pulse position are grouped together and are triggered by a pulse from the decoder shift register 69 delaying from 1 to at least 97 steps the original reset pulse on line 67, the units concerned with delays 62-97 being only flute. Optionally the decoder register can have the same form as scanner 16. Whenever a unit receives a trigger pulse, the simultaneous amplitude of the signal pulse is stored during the next cycle: this voltage level is copied into an R-C circuit with a control terminal, the voltage on which controls the rate of leakage through a diode, negative control voltage giving rapid decay and a percussion musical effect. The output voltage from the R-C circuit, in the corresponding keys in blocks 70, 79, 80, 85, biases the common point of a pair of opposed diodes blocking the path between the appropriately pitched tone generator and the input of the voicing filter. Maximum delay in the coupler control units is 60 steps after the 62nd pulse, i.e. pulse 122, leaving 6 pulses in the cycle for use in external control for modification of musical characteristics such as reverberation. The decoder shift register must be extended to 128 steps, or may take a form similar to scanner 16. Six sample and hold units store the control potentials between cycles. The circuitry is suitable for integrated circuit construction.