Patent GB-1442063-A (GB)
Title: Electronic musical instruments
IPC: G10H5/00
Filed: 1974-04-10
Abstract: 1442063 Electrophonic musical instruments NIPPON GAKKI SEIZO KK 10 April 1974 [1 April 1973 19 April 1973 7 May 1973 16 June 1973 (2) 11 Sept 1973] 15937/74 Heading G5J In an electronic musical instrument, the frequency of a tone generator and/or a formant filter is varied with time during the attack and decay periods of a note. As shown, a voltage controlled oscillator (VCO) 12 produces a tone signal with a frequency mainly determined by a voltage from keyboard 11 indicating which key is depressed. The tone signal is given a desired tone colour by a voltage controlled filter (VCF) 13 and a desired envelope by a voltage controlled amplifier (VCA) 14 before being fed to an output system 15, 16. Wave form generators 17, 18, 19 receive key depression and key release signals from the keyboard 11 and, using parameters stored in the waveform controlling circuit 20, generate waveforms which respectively modify the frequency of VCO 12 the characteristics of VCF 13 and determine the envelope provided by VCA 14. In modifications, waveform generator 17 may be omitted or fixed filters may be switched in or out of circuit between VCO 12 and VCF 13 by the waveform controlling circuit 20. Figs. 11 and 12 (not shown). VCO 12, Fig. 6, receives the tone pitch signal from the keyboard at 21, stores it on a capacitor 22 and through a high-impedence input buffer 23 derives a pitch voltage which is mixed with the waveform control voltage at 24 before being converted to a corresponding current at 25. The oscillator comprises a capacitor 27 which is discharged by transistor 30 every time its voltage reaches a level determined by Schmitt trigger 29. The frequency thus varies with the charging current provided by converter 25. V.C.F. 13, Fig. 7, comprises a current-controlled resistor 34 and a reactor (e.g. a capacitor) 36. The one signal from VCO 12 is applied at 32 and the waveform voltage from generator 18 is converted to e current to vary the reistor 34 to change the filter characteristics. A further signal from the waveform controlling circuit 20 may be applied at 39 to vary the feedback across amplifier 37 and thus the Q of the filter. VCA 14, Fig. 8 (not shown) comprises a current controlled differential amplifier having its in-phase and anti-phase outputs mixed to remove D.C. fluctuations. Waveform generators 17, 18 produce waveforms which rise rapidly to an attack level and immediately fall to a sustain level where they remain until key release when they return to their initial level. The waveform is produced on capacitor 51, Fig. 9. On key actuation capacitor 51 charges up to an attack level determined by a controllable voltage source 50 at a rate determined by controllable resistor 49. On reaching the attack level capacitor 51 is discharged to a sustain level at a rate determined by controllable resistor 55 and, on key release, to the initial level at a rate determined by resistor 57. Waveform generator 19, Fig. 10 (not shown) is similar. Waveform controlling circuit 20.-The parameters needed by the wave form generators are stored in circuit 20 as voltages on voltage dividers. In one embodiment the voltage dividers are potentiometers mounted on a board 71, Fig. 14, which has representations of the waveforms 75, 76, 77 thereon, the potentiometer controls 78 being located at the part of the waveforms they control. An arrangement is described for quickly copying the potentiometer settings into pre-set memory circuit boards for rapid retrieval of a particular group of settings and circuit boards with hard-wired voltage dividers may be provided to simulate particular instruments.