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Abstract

An audio synthesis circuit is disclosed that incorporates a phase accumulator, adder, sinusoid computing circuit, feedback controller, modulation controller and output accumulator. The audio synthesis circuit generates harmonically complex audio tones, which are output from the sinusoid computing circuit via the output accumulator through the use of frequency modulation of the phase of the audio tones. Instead of feeding back the audio tone to modulate the current phase, the disclosed audio synthesis circuit feeds back the current phase, which is converted by the feedback controller into a scaled feedback factor generated through a process using a waveform computing circuit that, without log-linear conversion, computes a preset cyclical function at an argument equal to the current phase. The feedback factor is then added to the current phase to generate a modulated phase value. The audio synthesis circuit can be used in a time-multiplexed fashion so that multiple audio tones, or operators, can be computed in a single audio synthesis cycle and then combined to form voices/channels. Each audio synthesis cycle can be divided into as few as 0 or as many as 48 time slots, meaning that as many as 48 operators can be played simultaneously. The disclosed circuit provides a preset organization of the 48 operators into 12 2-operator channels and 6 4-operator channels. These channels can be played in various system modes, including backward-compatible 2- and 4-operator modes in which the programming of the operators is restricted, and an enhanced mode, in which the operators can be freely programmed.

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First Claim