The 6581 Sound Interface Device (SID) is a single-chip, 3-voice electronic music synthesizer/sound effects generator compatible with the 65XX and similar microprocessor families. SID provides wide-range, high-resolution control of pitch (frequency), tone color (harmonic content), and dynamics (volume). Specialized control circuitry minimizes software overhead, facilitating use in arcade/home video games and low-cost musical instruments.



The 6581 consists of three synthesizer "voices" which can be used independently or in conjunction with each other (or external audiosources) to create complex sounds.
Each voice consists of a tone oscillator/waveform generator,an envelope generator and an amplitudemodulator.
The tone oscillator produces four waveforms at the selected frequency, with the unique harmonic content of each waveform providing simple control of tone color. The volume dynamics of the oscillator are controlled by the amplitude modulator under the direction of the envelope generator. When triggered, the envelope generator creates an amplitude envelope with programmable rates of increasing and decreasing volume.
In addition to the three voices, a programmable filter is provided for generating complex, dynamic tone colors via subtractive synthesis.
Please note that the SID is not a FM-based synthesizer, like the Yamaha OPL series !!

SID allows the microprocessor to read the changing output of the third oscillator and third envelope generator. These outpus can be used as a source of modulation information for creating vibrato, frequency/filter sweeps and similar effects. Two A/D converters are provided for interfacing SID with potentiometers. These can be used for "paddles" in a game environment or as front panel controls in a music synthesizer. SID can process external audio signals, allowing multiple SID chips to be daisy-chained or mixed in complex polyphonic systems.

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