Atari AMY

The Atari AMY (or Amy) was a 64-oscillator additive synthesizer implemented as a single-IC sound chip. It was initially developed as part of a larger effort to develop a 16/32-bit workstation known as Sierra, but this project was canceled in 1984. For a time, AMY was slated to be included in updated versions of the Atari 8-bit family, but this did not occur before development of that line was discontinued as well. The technology was later sold, but when the new owners started to introduce it as a professional synthesizer, Atari sued, and work on the project ended.

The AMY was based around a bank of 64 oscillators, which emit sine waves of a given frequency. The sine waves were created by looking up the amplitude at a given time from a 16-bit table stored in ROM, rather than calculating the amplitude using math hardware. The signals could then be mixed together to perform additive synthesis. The AMY also included a number of ramp generators that could be used to smoothly modify the amplitude or frequency of a given oscillator over a given time. During the design phase it was believed these would be difficult to implement in hardware, so only eight frequency ramps are included.

Sounds were created by selecting one of the oscillators to be the master channel, and then attaching other oscillators and ramps to it, slaved to some multiple of the fundamental frequency. Sound programs then sent the AMY a series of instructions setting the master frequency, and instructions on how quickly to ramp to new values. The output of the multiple oscillators was then summed and sent to output. The AMY allowed the oscillators to be combined in any fashion, two at a time, to produce up to eight output channels. The output was then converted to analog in a separate (user-provided) digital-to-analog converter.

While the additive synth system works well for sounds with a narrow spectrum, it is not useful for wider spectrum sounds like white noise. To fill the need to generate the sounds of explosions, jet engines and similar sounds, AMY also included random noise generators that could be mixed into the master oscillator to randomly shift the output.

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