Soundstream

Soundstream Inc.

The corporate logo of Soundstream, Inc.
Industry	Digital Audio
Founded	Salt Lake City, Utah (1975–1985)
Founder	Dr. Thomas G. Stockham, Jr
Soundstream Technical Specifications
Frequency Response	Flat from 0 Hz to 21 kHz
Wow and Flutter	Unmeasurable
Total Harmonic Distortion	Less than 0.004% at 0VU
Signal-to-Noise Ratio	Better than 90dB RMS, Unweighted
Dynamic Range	Better than 90dB RMS, Unweighted
Crosstalk	Less than -85dB
Print-through	None
Sampling Rate	50,000 per second
Digital Format	16 bits linear encoding / decoding

Soundstream Inc. was the first audiophile digital audio recording company, providing commercial services for recording and computer-based editing.^[1]

The company

Soundstream was founded in 1975 in Salt Lake City, Utah by Dr. Thomas G. Stockham, Jr. The company provided worldwide on-location recording services to Telarc, Delos, RCA, Philips, Vanguard, Varèse Sarabande, Angel, Warner Brothers, CBS, Decca, Chalfont, and other labels. It also leased or sold some recorders (a total of 18 were manufactured). Although most recordings were of classical music, the range included country, rock, jazz, pop, and avant-garde.

The first live digital recording, that of a symphony orchestra, was made in 1976 by Soundstream's prototype 37 kHz, 16-bit, two channel recorder.^[2] New World Records, which recorded the Santa Fe Opera's performance of Virgil Thomson's The Mother of Us All, provided Soundstream with a stereo feed from their multitrack console. Soundstream demonstrated its recording of the opera at the Fall 1976 AES Convention.^[3] Critiques of the recording, most notably from Telarc's Jack Renner and Robert Woods, led directly to the improved four-channel, 50 kHz sample rate recorder that was used for all of Soundstream's future commercial releases.^[4] (The New World Records issue of Mother of Us All was not from the digital recording made by Soundstream, but rather from the analog tape that New World recorded themselves.)

Also in 1976, Soundstream restored acoustic (pre-electronic) recordings of Enrico Caruso, by digitizing the recordings on a computer, and processing them using a technique called "blind deconvolution".^[5] These were released by RCA Records as "Caruso - A Legendary Performer". In subsequent years Soundstream restored most of the RCA Caruso catalog, as well as some RCA recordings by Irish tenor John McCormack.

Soundstream’s first commercially released recording (popular music on the Orinda label) in 1978 was a month shy of the world’s first digitally recorded commercial release, Ry Cooder's "Bop till You Drop". For the ensuing three years, 50% of all classical music recorded digitally used Soundstream equipment.

Unlike its competitors, Soundstream's analog circuitry was transformerless, permitting a frequency response to 0Hz (DC). This accounted for the "bass drum heard round the world"^[6][7] review of the 1978 Telarc recording of Frederick Fennell: The Cleveland Symphonic Winds.^[4][8] Soundstream collaborated with Telarc for several years, producing legendary symphonic recordings; the earliest ones are chronicled in Renner.^[9] The care with which Telarc selected and used its microphones and audio console, combined with the Soundstream recorder, created a gold standard for audiophile recording. Telarc has re-released many of its original Soundstream recordings in SACD format.

Soundstream recordings made before the advent of the CD were released as high-quality vinyl LP albums. Despite analog playback, many of these releases were sufficiently impressive to gain an early acceptance for digital audio.^[10][11] The recording industry’s transition to digital was further facilitated by the many demonstrations given by Dr. Stockham, whose articulate explanations of digital audio theory and practice were renowned.^[12][13]

In 1980, Digital Recording Corporation (DRC) acquired Soundstream. DRC attempted to develop a home digital player that would use a photographically reproducible optical card as opposed to the mechanically pressed CD.^[14] This effort was eclipsed by the rise of the CD, leading to the company’s demise in 1985.

The technology

The company developed its four-channel recorder in 1977. The Soundstream Digital Tape Recorder (DTR) consisted of a modified Honeywell 5600E instrumentation transport and analog and digital circuitry designed and built by Soundstream.

The Digital Tape Recorder

Promotional / publicity photo of the Soundstream Digital Tape Recorder.

The Digital Tape Recorder was a portable four-channel digital audio processor containing the analog to digital converters, tape-data recovery and clock generation circuits, and the digital to analog converters. External hardware (tape drive, editing system, and digital delay unit) connected to the DTR through connectors on the back panel. The unit measured 20"x18"x10" and weighed 67 pounds.

Analog signals entered the DTR through standard XLR connectors at the rear of the unit. There, a differential input amplifier routed the signal through the front panel attenuation fader to the input low-pass (anti-alias) filter.

The filtered analog signal passed through a custom sample and hold and was digitized by an Analogic MP8016 16-bit Analog-to-Digital Converter operating at a 50 kHz sample rate. A three-bit sync pattern and an even-parity bit were added to each 16-bit sample to form a 20-bit word that was serialized and transmitted by interface electronics to the tape transport where each audio channel's data were written to two separate tape tracks.

During tape playback or while recording and monitoring from tape, the redundant tracks of recorded data from the transport were sent to data recovery circuitry. Because the data recorded on tape are necessarily bandwidth-limited, the data-recovery circuitry squared-up the data signals and then created clocks to match the incoming data streams. Additional circuitry located word boundaries and converted the data to parallel format. In the event of tape dropouts, an error-avoidance scheme selected the unaffected track's data.

The selected data were then clocked into an Analogic MP1926A Digital-to-Analog Converter at the original crystal-controlled sample rate. The analog signal from the converter was routed to the output low-pass (reconstruction) filter. Voltage and current gain sufficient for +20dBm into 150 ohms was provided by the output-buffer amplifier which signal was then output at the XLR connector on the DTR's rear panel.

The Honeywell tapedeck (or Honeywell transport)

Soundstream-modified Honeywell 5600e Instrumentation Tape Drives (HTD) used custom high-frequency 18-track record and playback heads. The two outer tracks were reserved for ancillary data - SMPTE time code and the like. The remaining sixteen tracks were used to record up to eight channels of digital audio - two redundant tracks for each audio channel. The two tracks in a redundant track pair were separated as widely as possible to minimize playback errors due to tape defects (dropouts) - audio channel one was recorded on tracks 1 and 9.

At the front of the HTD, Soundstream installed Track Selector hardware. The left side selector allowed the operator to choose which audio channel pair (1,2; 3,4) was assigned to which tape track pair (1,2; 3,4; 5,6; or 7,8). The right-side selector controlled the application of record circuitry power for each of the eight tracks.

The HTD initially used 1" Ampex 460 reel-to-reel tape at 35ips. Later, Soundstream switched to Ampex 466 tape which allowed for the slower tape speed of 30ips.

The Digital editing system

Soundstream’s digital editing system was the first instance of a computer used to edit commercial recordings. It consisted of a Digital Equipment PDP 11/60 computer running the DAP (Digital Audio Processor) editing software (written by Soundstream employee Robert Ingebretsen), Soundstream’s interface (the Digital Audio Interface) to transfer data between its recorder and the computer’s disks (a pair of Braegen 14" disk drives), digital-to-analog playback hardware, a text-based video display terminal for entering commands to operate and control the DAP software, and a storage oscilloscope to display the waveforms of the audio being edited or processed. For all intents and purposes, this system was the very first digital audio workstation. In addition to its own facility, Soundstream installed editing systems at Paramount Pictures (Hollywood), RCA (New York), and Bertelsmann (Germany). A system was delivered to the U.S. Department of Justice to aid the analysis of bootleg recordings.

Editing could be performed at sample accuracy (i.e., 1/50,000 of a second); any mixing was performed digitally.

The sound system in the editing room in the Salt Lake facility used a Threshold SL-10 preamp, a Sumo "The Power" amp, and Infinity RS4.5 speakers.

Ancillary equipment

Digital Audio Interface

The Digital Audio Interface (DAI) was the input/output path between the Digital Editing System and external hardware. The DAI received raw source data from session tapes and passed the data on to the editing system's computer for storage. Finished (edited) data passed through the DAI from the editing system's computer to a DTR for creation of a master tape. During the editing process, data from the editing system's computer passed through the DAI to a Digital Audio Conversion Unit (DAC Box) in the editing room.

The DAI resided in the Editing System's computer and contained a one-megabyte FIFO. Realtime input/output capacity was eight channels of 16-bit audio data at any of the then standard sample rates.

Digital Delay Unit

To allow for a preview channel during the LP cutting process, Soundstream built a digital delay unit (DDU). Digital data from tape could be delayed by a user selectable time: 3ms to 1.308s in increments of 5.12ms. Delay was accomplished by the use of a variable-depth FIFO or ring buffer.

S-1610 adapter

So that users of the Sony PCM-1610 Digital Audio Processor could take advantage of Soundstream's editing system, the company developed the S-1610 Adapter. The adapter was a bidirectional two-channel format converter. Data from the Sony PCM-1610 were converted to the format used by the Soundstream DTR so that the data appearing at the input to the Digital Audio Interface looked to the DAI as if it had come from a DTR. Similarly, finished (edited) data in Soundstream format were restored to the Sony format by the adapter. Sony data were imported/exported at either of the two sample rates 44.1 kHz or 44.1/1.001 kHz.

Any metadata in the Sony format were lost in the format conversion. This was a format conversion only, the adapter did not do sample rate conversion.

M adapter

So that users of the 3M Digital Mastering System could take advantage of Soundstream's editing system, the company developed the M Adapter. The adapter was a bidirectional eight-channel format converter. Data from the 3M Digital Mastering System were converted to the format used by the Soundstream DTR so that the data appearing at the input to the Digital Audio Interface looked to the DAI as if it had come from a DTR. Similarly, finished (edited) data in Soundstream format were restored to the 3M format by the adapter.

DAC box

Essentially derived from the DTR's playback circuitry, the DAC Box was a four channel device used by the Soundstream editors to audition audio data during the editing process. Audio played from the computer through the Digital Audio Interface into the DAC Box.

References

External links

• An article on Soundstream and the introduction of commercial digital recording in the United States