GB1409763A - Musical tone wave shape generating apparatus - Google Patents

Abstract

1409763 Electrophonic musical instruments NIPPON GAKKI SEIZO KK 12 Jan 1973 [17 Jan 1972 (3)] 1768/73 Heading G5J An electrical waveform generator comprises memories M 1 ... M m each storing a number N of samples of a sine wave of one of a harmonic series of frequencies f ... mf. Clock pulses at a frequency Nf from a generator 1, via an encoder 2 and decoders D 1 ... D m , simultaneously scan the corresponding samples in all memories repetitively; and the read-out signals, via respective variable-gain amplifiers VA 1 ... VA m , are mixed at a common output terminal 3 to constitute a complex waveform of fundamental frequency f. The output wave shape is determined by control units C 1 ... C m which set the amplifier gains according to predetermined input resistances Ra 1 ... Ra m etc. For example the resistors Ra 1 ... Ra m are connected to a manual control VR a which, with the said resistance values, determines the amplitude and waveform of a first signal; a second control VR b , via resistors Rb 1 ... Rb m , determines the amplitude and waveform of a second signal to be superimposed on the first; and so on. The fundamental frequency of the output signal is determined by the clock-pulse frequency Nf of the generator 1. Preferably each memory M (Fig. 2) comprises an array of potential dividers R 1a /R 1b ... R Na / R Nb each applying an analogue potential to the drain of one of an array of FETs T 1a ... T Na , whose sources are connected to a common output terminal T out . Excitation of each FET gate in turn by a clock pulse produces a stepwise output signal approximating a sine wave. Memory M 1 stores a single cycle, M 2 two cycles, and so on up to M m which stores m cycles. In a modification (Fig. 3, not shown) the digitized outputs from the memories (M a1 ... M am ) and the control units (A 1 ... A m ) are multiplied in multipliers (ML 1 ... ML m ), digitally added and converted to analogue form. In a further modification (Fig. 4, not shown) the control-unit input resistors are replaced by spectrum memories (SM 1 ... SM 20 ) each storing digitized harmonic-content signals for a desired wave. These signals, multiplied by digitized amplitude signals from units (A a1 ... A a20 ) and added to the weighted signals from other spectrum memories, are passed on to the respective harmonic-frequency multipliers (ML 1 ... ML m as in Fig. 3).