Variable frequency generator for polyphonic electronic music system

Abstract

Simultaneously played notes on a keyboard are automatically provided with different voice timbres. The assignment of voices to notes is by relative frequency-scale position within the chord. If four or more notes are played, the notes are scanned along the musical scale and the three lowest notes played and the highest note are sounded in different voices with the solo voice assigned to the highest note. Assignment of voices occurs automatically when fewer than four keys are played. One form of the system combines time multiplexed keying with priority coupling of the keying information to a plurality of voltage controlled oscillators through sample-and-hold memory circuits. Each oscillator has its own tone voicing circuits. In another preferred all-digital embodiment, the time division multiplex digital logic signals representative of the played keys are applied instead to a memory circuit and a comparator circuit. If the information stored in the memory from the previous scan cycle is the same as the information of the present cycle, thereby indicating no change in played keys, the comparator provides an enabling signal to a monostable and enable logic circuit. A priority selector circuit provides logic information representative of the three lowest keys played and the highest key played to the monostable and enable logic circuit. The monostable and enable logic circuit provides on four outputs information representative of the three lowest keys played and the highest key played and also information representative of the total number of keys played. This information is combined with the octave information and the note time slot information in four programmable counter circuits which divide four input frequencies from a rate scaler frequency generator to produce four tone signals having fundamental output frequencies f1 - fH corresponding to the three lowest notes and single highest note played. Also, the four programmable counter circuits provide control voltages corresponding to the played notes. The tone signals and control voltages are applied to voltage controlled gates and filter circuits which provide the necessary voicing to produce different orchestral effects on different notes. The resulting orchestral effect can be enhanced from an ensemble standpoint by controlled detuning of the four output frequencies, both within the chordal relationship and relative to other tones of corresponding pitch nomenclature under control of the same master oscillator. The outputs of the voltage controlled gate and filter circuits are applied to at least 2 output channels to avoid electrical cancellations when two programmable counters are assigned to the same note but slightly detuned.