GB1420085A - Electronic musical instrument - Google Patents

Abstract

1420085 Electrophonic musical instruments NIPPON GAKKI SEIZO KK 28 Dec 1972 [30 Dec 1971 (3) 22 Feb 1972 (2) 26 Feb 1972 (3)] 59821/72 Heading G5J In an electrophonic musical instrument instantaneous amplitude samples of a waveform are stored in analog form and means are provided to readout the samples simultaneously at a plurality of selectable rates and produce therefrom a plurality of musical tones. As described the instrument comprises upper and lower keyboards 1b. The operation of a key is detected by a key address code generator la which generates a sequence of binary codes corresponding to each key. The code has eight bits, four to determine the note, three to determine the octave and one to indicate upper or lower keyboard. The keyboard passes a signal to common logic circuit 3 when the code of any actuated key is generated. The logic circuit for achieving this is described, Fig. 2(a) (not shown). On the assumption that no more than ten notes will be required simultaneously, ten signal channels CN are provided. Common logic circuit on receiving a signal from the keyboard checks that there is not already a channel dealing with that key and if not writes the key address code into the memory 2 of a vacant channel. Memory 2 controls a counter 5 to read a wave shape out of either memory 11 or 12. The note bits of the code select one of twelve tone clocks respectively sixteen times the frequencies of the notes of the top octave; the octave bits control where in counter 5 the clock is connected and the upper/lower bit selects memory 11 or 12. In an alternative embodiment, Fig. 4 (not shown), there are separate tone clocks for all notes of all octaves. Attack and decay envelope samples are stored in the first sixteen and last forty-eight address of a memory 14. An envelope counter 6 started when a new key is depressed counts up to 16 reading out the attack waveform which is applied as a scaling factor to the inputs 11a, 12a of the memories 11, 12. Counter 6 then stops until restarted by release of the key to read out the decay envelope to memories 11, 12. The contents of counter 6 is also held during the decay in a truncate counter 7. If a fresh key is depressed while all channels are in use, the common logic 3 checks which channel has progressed furthest with a decay by feeding rapid pulses to all the truncate counters and seeing which overflows first. The overflow signal clears that channel and the new key address is written into its memory 2. If a key is depressed while the corresponding note is decaying, its channel is cleared and the attack starts afresh. The channels are connected in sequence to the memories 11, 12, 14 by a multiplexing counter 8. The memories preferably comprise resistors connected as voltage dividers with the stored sample corresponding to the tapping point, Fig. 5 (not shown).