User:Musimath/Systems Concepts Digital Synthesizer

Systems Concepts Digital Synthesizer The Systems Concepts Digital Synthesizer was a unique special-purpose digital signal processing computer designed for audio and music applications developed in the mid-1970's by Peter Samson of Systems Concepts, a small computer peripheral manufacturing company in San Francisco. It was an important landmark in the transition from the use of general-purpose computers to real-time systems for music and audio. It was on the vanguard of the revolution that transformed the music industry from analog to digital technologies beginning in the 1980’s.

Exactly one machine, nicknamed the "Samson Box", was built. It was commissioned in 1975 by John Chowning and Andy Moorer, two of the principals of the Center for Computer Research in Music and Acoustics (CCRMA) at Stanford University. It was delivered to CCRMA in 1977, and was placed into service in early 1978. At that time, CCRMA was a project of the Stanford Artificial Intelligence Laboratory (SAIL). Under the direction of John McCarthy, SAIL was housed in the Donald C. Power Laboratory building in the hills above the Stanford University campus. The Samson Box served for a decade as the principal real-time music generation system at CCRMA, serving researchers, composers, musicians, psychoacousticians, and computer scientists. Over its lifetime, it facilitated many research projects and more than one hundred finished compositions, many of them award-winning.

Prior to the invention of real-time digital synthesizers such as the Samson Box, computer music research and composition relied on slow general-purpose mainframe computers to synthesize sound. Though general-purpose machines could record and play back high-quality multi-channel digital audio, even the fastest main-frame computers could not calculate music of useful complexity in real time. To calculate interesting results on mainframes required ratios of compute-time to real-time that were on the order of a magnitude or more, meaning that users might wait hours or days to hear the results of a brief musical excerpt. Given that the sounds being generated were often highly experimental in nature, the extremely slow turn-around time was a serious impediment to development of digital music. The Samson Box provided a way to calculate digital audio of useful complexity in real time so the field could move forward more quickly.

Though the Samson Box was but one of a number of digital synthesizers developed in that time frame, it was uniquely powerful. A set of programmable signal processing elements could be patched together into arbitrary topologies via a summing scratchpad memory called "sum memory." The processing elements included 256 waveform generators, 128 signal modifiers, as well as a large (64K-word) memory that could be used for delay lines, reverberation, and table lookup functions.

The waveform generators included segmented envelope generation and oscillator circuitry. Generators could produce sine, band-limited sum-of-cosine, and analytic functions including square, pulse, and sawtooth waveforms. Generators could be combined via sum memory to provide multi-carrier and multi-modulator frequency modulation and amplitude modulation synthesis. Ganged together, generators could perform sample-synchronized additive synthesis. The modifiers could perform mixing, modulation, filtering, as well as logical operations on signals. Modifiers interfaced to the 64K-word memory via delay unit generators provided for reverberation and table lookup. Four channels of linear PCM audio were available via Digital to Analog Converters. The Samson Box could also read audio data files and write files to disk storage for further processing.

The Samson Box was designed to be controlled by an external computer as a peripheral. At first, the Samson Box was controlled by a Digital Equipment Corp. (DEC) PDP-6 mainframe computer executing a dedicated application that received synthesizer commands from SAIL's DEC PDP-10 computer via a shared memory. The PDP-6 fed commands on demand to the Samson Box in real time. Later, after CCRMA became an independent research unit at Stanford, the Samson Box was controlled by a Foonly F2 (and later still, a Foonly F4) computer, designed by David Poole.

At first, the Samson Box was used as a special-purpose real-time batch processor of music. Software for the Samson Box was developed by CCRMA staff and graduate students using the SAIL WAITS operating system. Andy Moorer, then a SAIL systems programmer, architected the software system and wrote the PDP-6 executive that controlled the Samson Box in real time. Mark Kahrs and Ken Shoemake provided code libraries for resource allocation, parameter loading, scheduling, command assembly and disassembly. A compiler (MUSBOX) was written by Gareth Loy using these code libraries that ran on the PDP-10. Loy adapted the lightweight process discipline of the SAIL programming language to read scores in MUSIC-N notation: MUSBOX read "note statements" from a text file, which specified time-based parameters to control synthesis. Each note statement contained an instrument name, a begin time and duration, and a list of additional parameters, such as pitch and loudness information. The compiler parsed note statements, created SAIL instances of the named instruments, and initialized the instrument's local variables with the parameters. A time-based hierarchical scheduler in the compiler received scheduling requests from the instances as they executed. The instances claimed synthesizer processing resources, then emitted synthesizer instructions appropriate to generate or process sounds, each according to its software design. The synthesizer command stream output from the compiler was first stored in a file in the PDP-10 filesystem, and could then be transferred in real time to the Samson Box via the PDP-6 to realize a composition. This system provided rapid prototyping of musical works and research projects.

The first production use of the Samson Box — in December, 1978 — was to recast John Chowning's landmark mainframe composition Turenas, to be performable in real time. After that, the Samson Box supported hundreds of compositions and research projects for over a decade at CCRMA. Later, user controls such as knobs and an electronic organ keyboard were connected to the Samson Box via the PDP-6, and it was then capable of being performed in real time. A KIM-1 microprocessor (based on the 6502 microprocessor architecture) was developed by Andy Moorer to sample the user controls and forward data to the PDP-6, and thence to the Samson Box. Additional software was contributed by many users, including Julius Smith, David Jaffe, John Strawn, Marc LeBrun, Jan Mattox, Paul Wieneke, Xavier Serra and others. Bill Schottstaedt developed a new compiler (PLA) in 1983.

Problems

Progress in digital technology eventually rendered the Samson Box obsolete, and it was retired April 2, 1992. After being decommissioned, it was moved to the permanent collection of the Musée de la Musique, part of the Cité de la Musique, in Paris, France.

Recently, a Samson Box emulator (sam.c) has been written by Bill Schottstaedt and Mike McNabb that runs in realtime on a standard laptop.

External links

• example.com