Atari's AMY (or Amy) was a 64-oscillator additive synthesizer implemented as a single-IC sound chip. For a time, AMY was slated to be included in newer versions of the Atari 8-bit family, but this did not occur before development of that line was discontinued. The technology was later sold, but when the new owners started to introduce it as a product, Atari sued, and work on the project ended.
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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. There were only 8 frequency ramps, as they appeared to be more difficult to build during the design stage.[1][2]
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 8 output channels. The output was then converted to analog in a separate (user-provided) digital-to-analog converter.[2]
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.[1]
The AMY was particularly useful for digital sound playback given the limited memory and bandwidth resources available at the time. An input sample could be run through an Fast Fourier transform to extract the spectral pattern, and then that pattern could be input to the AMY to set up the oscillators. The result is a highly accurate rendition of the original signal, but reduced to a handful of parameters that could easily be stored. That pattern could then be shifted up or down simply by changing the frequency of the master oscillator, with the slaved oscillators following those changes naturally. In one experiment, telephone-quality voice audio was produced using this method, requiring only 2400 baud of bandwidth.[1]
The AMY was developed as an experiment within the Advanced Technologies Group (ATG) of Atari, starting in 1983 and then known as Project GAZA. The system design was based on Hal Alles' experimental work at Bell Labs during the 1970s, which produced a similar system that required several racks of equipment to implement the so-called "Alles Machine". Several of Alles' solutions to particularly thorny implementation issues were used in GAZA.[1]
At the time, it was intended to be used in a new Motorola 68000 machine being designed, which also used a new graphics chip known as "Rainbow". The GAZA team was led by Gary Sikorski, and the primary architects were Scott Foster and Steve Saunders. The single-chip implementation was handled by Sam Nicolino, while John Palevich and Tom Zimmerman wrote support software.[1]
AMY was announced in an Atari-internal mailing list in March 1984, with a short description and a June estimated time frame for shipping the first version, the AMY-1, with volume quantities available that December.[1] The first versions would run up to 5 MHz, but a second run improved this to 10 MHz. Spec sheets used 4 and 8 MHz and basic clock speeds, respectively.[2] Like most ATG projects, AMY was not the result of a specific product requirement, and at the time there were no planned uses.
In July, Jack Tramiel bought Atari from Warner Communications and quickly dismantled the majority of Atari's engineering departments. During this process they came across the AMY team, who persuaded them to adapt it for use in the 8-bit machines. These machine's sound capabilities were lacking in comparison to contemporary machines like the Commodore 64, which the AMY would address convincingly. The result was the 65XEM project, which combined the existing 65XE with the AMY.[3]
First shown publicly at the Consumer Electronics Show in January 1985, the XEM carried a premium $30 to $50 above the basic 65XE, which was also being launched at the same show. However, as the company's focus quickly shifted from the 8-bit line to the new Atari ST's being launched at the same time, the XEM was shunted aside and never released commercially. A few prototypes were built, some of which later found their way into the hands of private collectors.[4]
Tramiel later decided to sell off the technology, and reached an agreement with the Millwaukee-based company, Sight & Sound. They developed a new version with 32 oscillators, along with a rack-mount MIDI synthesizer based on it. However, as they were preparing to ship the product, Atari threatened to sue them, and the system never shipped.[1]