Bell Labs Digital Synthesizer

The Bell Labs Digital Synthesizer, better known as the Alles Machine or Alice, was an experimental additive synthesizer designed by Hal Alles at Bell Labs during the 1970s. The Alles Machine used 64 computer-controlled oscillators whose output was mixed to produce a number of discrete "voices" for output. The Alles Machine has been called the first true digital additive synthesizer, following on earlier Bell experiments that were partially or wholly implemented as software on large computers. Only one full-length composition was recorded for the machine, before it was disassembled and donated to Oberlin Conservatory's TIMARA department in 1981. Several commercial synthesizers based on the Alles design were released during the 1980s, including the Atari AMY sound chip.

The Alles Machine consisted of three main parts; an LSI-11 microcomputer, the programmable sound generators, and a number of different input devices. The system was packaged into a large single unit, and weighed 300 pounds – the designers optimistically referred to it as being portable.

The microcomputer was supplied with two 8-inch floppy disk drives (from Heathkit, which sold their own LSI-11 machine, the H11) and an AT&T color video terminal. It was connected to a customized analog-to-digital converter that sampled the inputs at 7 bit resolution 250 times a second. The input devices consisted of two 61-key piano keyboards, four 3-axis analog joysticks, a bank of 72 sliders, and various switches. Any of the controllers could be used to control any parameter, under program control. The inputs were interpreted and then used to generate outputs that were sent to the sound generators as a series of parameters. The bandwidth needed to control the synthesizer was quite limited. The computer could process about 1,000 parameter changes per second before it would bog down in the CPU.

The sound generator was fairly complex, containing 1,400 integrated circuits. The first bank of 32 oscillators were used as master signals, and generally meant the system had up to 32-note polyphony (see below). A second set of 32 oscillators was slaved to one of the masters, generating the first N harmonics, where N was from 1 (first harmonic) to 127. Additionally there were a bank of 32 programmable filters, 32 amplitude multipliers, and 256 envelope generators. All of these signals could be mixed in an arbitrary fashion into a bank of 192 accumulators. These were then sent to one of four 16-bit output channels, and from there to a digital-to-analog converter for output.

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