Patent GB-1286128-A (GB)
Title: Signal processing arrangement for an electronic musical instrument
Inventor: KAWAMOTO KINJI
IPC: G10H1/02
Filed: 1969-10-14
Abstract: 1286128 Electrophonic musical instruments MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 14 Oct 1969 [21 Oct 1968] 50348/69 Heading G5J A tone generator 101 generates a tone consisting of a fundamental together with a series of exact harmonies, and the output is fed to a frequency shifter 201 which moves all the frequencies up or down by a given amount ## which is preferably a sub-audio frequency so that the inharmonicity function Y (n) = fn/nf1, where fn is the frequency of the n'th partial and f 1  is the frequency of the fundamental, which is equal to unity for all n for an exact sequence of partials becomes:- The muscial interest of the sound is thus enhanced and in the former case, it is possible to match the inharmonicities of conventional instruments, e.g. the piano, as in Fig. 3 (not shown). A number of tone generators and frequency shifters can be combined, together with a keyboard switching system and a tone filter to form a musical instrument, the sequences of exact harmonics generated by derives 101 . . . 104 . . . &c. preferably being biased so that the output frequencies are those of a musical scale. The quantities ## for each output tone may be constant or variable. In the case of a single tone generator of different exact harmonic frequency sequences, the shifting frequency may be dependent on the frequency sequence, Fig. 4 (not shown). In Fig. 6 (not shown) the tones are grouped and fed through a lesser number of frequency shifters, and in Figs. 7, 9 and 10 (not shown), the tone frequencies are added and filtered into frequency bands which are separately shifted. In Fig. 10 (not shown) there are four frequency bands, the lowest being shifted downwards, and the upper two shifted upwards, the remaining band being unchanged, Fig. 11 (not shown). This system provides octaves at the extremes of the frequency range which are wider, and more pleasing to the ear than the exact 2:1 ratio of the tone generator, Fig. 8 (not shown). The system of Fig. 10 (not shown), uses generators providing 12 semitones within an octave, with frequency dividers to provide a set of tones with exact harmonics for the filters and frequency shifters. The tone generators may be replaced by an input consisting of the sounds of conventional musical instruments, or other sound sources, whose tonal properties are thus modified. Means to produce the frequency shift may be an oscillator of frequency ## producing two signals in quadrature, together with a phase-shifter producing two signals of frequency f in quadrature from a single input of frequency f, and these when multiplied will give frequencies #Œ##, Fig. 12 (not shown). The multiplying means may consist of an amplitude modulator, modulating a frequency f with the frequency ##, and a phase inverter to remove the carrier leaving sidebands at #Œ##, Fig. 13 (not shown). Alternatively the frequency fa, Fig. 41 (not shown), may be respectively modulated with frequency cf with subsequent filtering out of the lower side band, modulating the resulting frequency with a frequency fc<SP>1</SP> and filtering the result to give a frequency #α-##, where ## = #c-#c<SP>1</SP> Fig. 15 (not shown).