Patent GB-1440488-A (GB)
Title: Electronic musical instrument
IPC: G10H7/04
Filed: 1973-12-13
Abstract: 1440488 Electrophonic musical instruments NIPPON GAKKI SEIZO KK 13 Dec 1973 [14 Dec 1972 (4) 13 April 1973 6 July 1973 (2)] 58057/73 Heading G5J In a computer organ, in which a key assigner produces a key address code to control a tone waveform generator and key depression and release control signals to control an envelope waveform generator the outputs of the waveform generators being multiplied together, the assigner, waveform generators and multiplier have synchronously driven shift-registers to enable the waveforms of a plurality of simultaneously played notes to be computed in a time-sharing manner. General organization of the organ.-The keys in keyboards 1 have first contacts 1a which break at the beginning of key actuation and second contacts 1b which make on complete actuation. All the key switches are scanned sequentially with a stepping rate of 12 Ás by a key data signal generator 2 which generates first and second signals on operation of the first and second switch contacts respectively at a time-slot in the scanning cycle corresponding to the identity of the actuated key. The key assigner 3 receives the first and second signals and, operating in synchronism with the scanning, applies a binary digital tone code to a frequency information memory 4. The key assigner may allot notes to channels in the circuitry or in a modification, there may be one channel reserved for pedal tones. Key assigner 3 also produces a signal TRS representing the time delay between the operation of the first and second switch contacts and hence the touch on the key, a signal ES when the second contact closes to initiate attack, a signal DIS when the second contact opens to initiate decay, and a signal PES to provide percussion effects when DIS follows ES rapidly. Counters P1C, P2C and EC read envelope shapes from analogue memories P1M1, P1M2, P1M3, P2M1, P2M2, P2M3, E1M1, E1M2, E1M3 which are applied to modify the wave shapes produced by the analogue tone wave shape memories 6a-6e through a buffer BF. The envelope amplitude is controlled by a memory TRM selectively read by a counter TRC enabled by the touch responsive signal TRS. Wave shape memories 6a-6e also receive signals from the frequency information memory 4 to determine the spacing of the samples read out from the memories and hence the tone frequency produced. The logic circuits of the key assigner are described, Fig. 9 (not shown). Key data signal generator (Fig. 3).-The instrument has in general four keyboards (three manual and one pedal) each divided in general into four blocks, each block having in general sixteen keys. A key address code is generated by an 8-stage binary counter KAG1 driven a 12 Ás clock #2. Digits K1K2 represent the keyboard, B1B2 the block and N1N2N3N4 the key within the block. The outputs of a digital to individual decoder D1 are connected to corresponding break contacts S4K3 &c. of each block. The common bus, e.g. S4B of each block is connected via one of the AND gates Y0-Y13 which are opened in sequence by a decoder D2 and OR gates OR1, OR2 to the output where any open contact shows as a first key signal. A delay circuit DF acts as a waveshaper by detecting the key signal during one scanning time slot in which it rises gradually and transmitting it as a good rectangular pulse in the next time slot. The logic is designed to cope with any keys of blocks of keys which are not provided in any particular organ and also to eliminate the effect of contact chatter, Figs. 7A, 7B (not shown). A similar arrangement is used to generate the second key signal, Fig. 4 (not shown). Generation of the envelope (Fig. 13).-When the signal to start attack ES is received on terminal TE1, pulses from attack clock AP are applied to a counter comprising an adder AD4 and shift-register SR4. The increasing count reads out successive analogue samples from memory EM until the end of the attack period indicated by a signal from OR gate OR31 which blocks the passage of attack pulses through gate A81. The envelope amplitude is then sustained at this value until the decay start signal DIS on terminal TE2 opens gate A82 for the passage of pulses from decay clock DP. Counting continues until the decay waveshape has been read out of memory EM whereupon note finish signal from gate A80 closes both gates A81, A82 and initiates a clear signal CC from the key assigner to clear the circuits of the organ of that note. If a further key is operated while 12 notes are already sounding the key assigner detects whether any of the notes are decaying, and if so the decay of the most decayed note is accelerated by a "truncate" counter b in Fig. 13 so that this note may be replaced by the new note. Percussion counters P1C, P2C and the touch responsive counter TRC and their associated memories operate in a manner similar to the envelope counter EC and memory EM. Tone frequency generation (Fig. 10).-At each address in the memory 4 defined by the code K2, K1, B2, B1, N4, N3, N2, N1 is stored a 15- digit binary number n 1 -n 15  representing the corresponding frequency. The number n 1 -n 15  is applied to adders AD1-AD3 and put in the first stage of shift registers SR1-SR3 which have 12 bits so as to be able to deal with 12 notes at once. The number is stepped through registers SR1-SR3 and numbers are added corresponding to other notes by a 1 Ás clock # 1 . Every 12 Ás a number in SR1-SR3 reappears and is added to the same number n 1 -n 15  from memory 4 and replaced in the first stage of SR1-SR3. Thus a number in a given stage of SR1-SR3 increases in 12 Ás steps thus: (n 1 - n 15 ), 2(n 1 -n 15 ), 3(n 1 -n 15 ) .... The number in the most significant shift register SR3 is used to read out analoque samples from tone waveform memories 6a-6c. The sampling number may be reduced when dealing with high frequencies so that the highest harmonic concerned does not approach the sampling frequency too closely. In an alternative logic system the key address code is held in a memory and the frequency information is read from a lower speed read only memory during the 12 Ás period between the time-slots of a given channel, the information being added in the later channel slot. Chorus effect may be achieved by providing a plurality of frequency information memories with slightly differing information in each. These may be used in parallel for all notes, Fig. 23 (not shown) or each assigned to a par. ticular keyboard Fig. 24 (not shown). In another system Figs 25 and 26 (not shown) an adder alters the information from the memory 4 and the altered and unaltered values are applied to separate counters 5 and memories 6. The numbers may be altered by a fixed number or a by a proportion 2<SP>-n</SP> of themselves. Reference has been directed by the Comptroller to Specifications 1,312,161, 1,312,162, and 1,317,385.