Jump to content

Bell Laboratories Alles LSI-11 Microcomputer Controlled Digital Sound Synthesizer

   (0 reviews)

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; a 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 was used as master signals and generally meant the system had up to 32-note polyphony (see below). The 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 was 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.

The actual waveforms were generated by looking up the amplitude for a given time from a 64 kWord ROM-based table. Alles used several tricks on the table in order to reduce the amount of math the system needed to run in the controller CPU. In one instance, a multiplication was avoided by looking up two numbers from the table and subtracting them, as it was noticed the result was the same as a multiplication of two related numbers. Running everything was a set of 255 times with 16 FIFO stacks for events. The controller posted events into the queues which were then sorted by timestamp and fed into the generator in order.

The Bell Laboratories LSI-11 Microcomputer Controlled Digital Sound Synthesizer was designed to be a Portable Digital Sound Synthesis System. The complete real-time digital sound synthesis system has been
constructed. In one compact unit.

All the devices are bus interfaced to the LSI-11 computer and all the control words appear in LSI-11 address space (6k words). Approximately 1400 IC's are used in the entire system.

All of the system components have been designed to complement each other's capabilities. Special purpose hardware was constructed to perform those tasks which are repetitive and time-consuming (timekeeping and performer input filtering).

Since there are no hard-wired connections between the input devices and the synthesizer hardware, and since synthesizer interconnections are accomplished through program loaded control registers, the whole system may be used in a variety of ways. For example:

A. All the control parameters may be specified in real time and at performance time.

B. Several files may be prepared in real time but before the performance. Then at performance time, the files may be played with some subset of the control parameters supplied during the performance.

C . Files may be prepared and/or edited in nonreal time, incrementally improving the original performance.

The total real-time synthesis capacity depends, of course, on the type of synthesis techniques and configuration used. The LSI-11 and floppy disc multiple file system can support ~1000 parameter changes/sec. These parameters may be used to specify frequencies, envelopes, configuration changes, graphics displays, etc. This data rate should be able to generate ~100 reasonably complex notes per second.

This system is perhaps the first representative of a new generation of musical instruments that combine in one relatively portable unit all the hardware and interfaces necessary to produce in real time and in a performance environment sounds approaching the complexity of a modest orchestra.

Technical Specifications
Type: Digital
Synthesis: Additive, Frequency Modulation, ROM, Subtractive
Oscillators: 64
Waveforms: Additive, ROM, Sine
ROM Size: 64K
ROM Resolution: 16 bit
Osc Modulation: Continuous Controller, Envelope, Input, Keyboard, Knob, LFO, Oscillator, Sequencer
Envelopes: 256
Filters: 32
Types: 12dB Slope (2-pole), Low Pass
Filter Modulation: Envelope, Input, Keyboard, Knob, Oscillator, Sequencer
Polyphony & Tuning
Polyphony: 32
Timbrality: 2
Tuning: Standard
Modes: Polyphonic, Split
Patches RAM: 1
Storage: Floppy 8 inch
+ 2 seconds Reverb.
+ 64 taps.
+ 256 steps
+ 16 sequences
Chips and Operating System
Digital Equipment Corp. LSI-11 computer.
Case: Desktop, Keyboard
Case Details: Dual Keyboards,
Keyboard: 61 keys, Non-weighted, Plastic
Controls: Buttons, Knobs, Sliders, Joy Stick, Sequencer
Display Type: LED, Backlit
Display Notes: 8" CRT
Dimensions (WxDxH): 42 x 18 x 25 inches
Weight: 300 lbs
Audio Output Connections: XLR, Stereo Main, Stereo 2
Audio Output Count: 4
Inputs: 2
DAC Bits: 16
DAC Frequency Rate: 30 khz
Year Released: 1976
Units Made: 1
Used By
Roger Powell, Laurie Spiegel, Larry Fast
Design Notes:

Designed by Hal G. Alles at Bell Laboratories Murray Hills New Jersey.

The Alles Machine was highly influential within the industry, but the cost of implementation was so high that it was some time before machines based on its principles were available at a price point most musicians could afford.

Crumar of Italy and Music Technologies' of New York collaborated to form Digital Keyboards in an effort to re-package the Alles Machine. The result was a smaller two-part system, with a Z-80-based microcomputer and disk drives as one unit, and a single keyboard and limited set of input sliders as the second unit. Known as the Crumar General Development System, or GDS, it was released in 1980 for $30,000. It was sold to studios that needed a flexible system that could guarantee the same performance time after time. Analog synths of the same era were subject to environmental changes in the input controls that meant every performance, even after a short delay, would be different. Wendy Carlos owned a GDS and used it on the Tron soundtrack. She was also one of the instrument's most devoted users, and still uses it to this day.

Further work on the same basic concept produced the lower-cost Synergy, released in 1981. The Synergy removed the computer component, and re-packaged the entire system into a case with a 77-key keyboard. Another additive synth reached the market at about the same time, the Con Brio ADS200, at the slightly lower price of $20,000. Neither the Con Brio or GDS sold well, while the Synergy managed to find some market share. However, when the famous Yamaha DX7 was released in 1983, it quickly took over the market. The DX7's FM synthesis offered the same basic control over output sound as an additive synth, but could duplicate the effects of many ganged oscillators in as few as two. Its $2,000 price point eliminated any competition from the additive synths. Production of the Synergy ended in 1985.

A final version of the original machine was produced after Digital Keyboards was shut down in early 1985. Digital Keyboards' chief designer, Mercer Stockell, decamped and formed Mulogix with Jim Wright and Jerry Ptascynski. The Mulogix Slave 32 was a Synergy re-packaged into two rack-mount modules with a MIDI interface. The Slave 32 could read and write EPROM cartridges from the Synergy.

In 1981, Ceasar Castro and Alan Heaberland introduced their Casheab S-100 board. It also bore striking resemblance to Alles & Bayer's design. One early adopter was Roger Powell who designed his "Databoy" system around it. Powell used a home-brew 8800 system to scan the keyboard and modulation controllers as well as provide access to a custom library of sounds he created.

Starting in 1984, Atari started an effort to develop a single-chip implementation of the Alles Machine in their Sierra project. The resulting AMY 1 chip used 64 oscillators and added noise generators to provide special effects needed in games. However the AMY was never released, and a 3rd party effort to produce a low-cost synth based on the chip ended when Atari threatened a lawsuit.
Related Synthesizers

  Report Synthesizer

User Feedback

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.


  • Create New...