GB1394858A - Integrated circuit synthesis and bright wave organ system - Google Patents

Abstract

1394858 Electrophonic musical instruments HAMMOND CORP 20 July 1972 [29 Sept 1971] 34085/72 Heading G5J In an electronic organ the frequency-dividing and keying circuits for a set of octavely-related notes are in a single i.e. package. A given note is synthesized from a fundamental (f), harmonics 2, 3, 4, 5, 6 and 8, a sub-fundamental (f/2) and a sub-third (3f/2). A single i.e. (Figs. 1A and 1B), supplies all the frequencies for synthesizing the C notes of five octaves, a second i.e. (not shown), supplies the frequencies for the C # notes, and so on. In other embodiments (Figs. 4-6, not shown), there are fewer i.c.s and each provides two or more notes in each octave. The proportions of the different frequencies to give the desired tone colour are determined by drawbars 152 (Fig. 3), which set the voltages on nine rails connected to terminals 170-184 of all the i.c.s. In operation, pressing, for example, the playing key for C 2 closes contacts 171 (Fig. 3), whereupon a keying voltage, having an envelope determined by circuit 169, is fed to one of the terminals 168 of the C i.e. and thence to a block 136 (Fig. 1A), of nine keying circuits. There is one such block 136-144 for each C note. Each keying circuit comprises a pair of FETs (146, 148, Fig. 2, not shown). The keying voltage turns on all the transistors (148) of the block 136. Each keying circuit receives a square wave of appropriate frequency (the particular harmonic of the particular note), and a D.C. input from the appropriate 152 to set the level of this harmonic. The outputs of the keying circuits are fed via terminals 190-204 (Fig. 1B), to band-pass filters which convert the square waves to sine waves, and are then combined to give the synthesized note. The required frequencies for all the components of all the C notes are derived from three divider chains 16-40, 60-74 and 106-126 which are included in the C i.e. The input terminals of the divider chains are fed from clock generators. There may be twelve clock generators, giving frequencies C 8 to B 8 , in which case the harmonics are not exact, other tones in the scale being borrowed. Alternatively, there may be thirty-six clock generators, to give exact harmonics, in which case the fundamental and harmonic clock generators may be modulated differently to produce special vibrato effects. Where two or more divider chains are fed from the same clock they are synchronized by means of reset inputs 52, 94, 134 and synchronizing outputs 48, in order to avoid cancellation when notes are played together. The i.e. may include additional circuits (Figs. 7 and 8, not shown), to provide an auxiliary "bright wave" system. The square waves on lines 14-42 (Fig. 1A), for example, are combined to produce staircase waveforms which are then passed to external formant, control and output circuits.