Restoration Tips & Notes Working with audio media (mostly tape) restoration

2006-03-19

Digital Audio-VCR

Filed under: — Richard L. Hess @ 15:43

Major updates: 2008-09-13, 2011-06-19

While dedicated reel-to-reel and later cassette-based digital audio recorders were being developed, for stereo use it became obvious that the high bandwidth of analog video recorders could be used for recording a digital audio bitstream. Also, video links were used to transmit high-quality digital audio around the world.

Until the late 1990s, many CDs were mastered on a Sony PCM-1610 or later PCM-1630 system which used 3/4″ U-Matic video cassettes. Tapes made on these systems should interchange with each other. Resources for transfer: Sonicraft, New Jersey — Ted Carson, MusicLane Mastering (905) 852 2193, Uxbridge, Ontario, Canada.

JVC had a competing and incompatible mastering system called the DAS-90 and later the DAS-900. You can see a brochure here (thanks, Don N.). The processor in the DAS-90 system was called (at least at one point) the BP-90 while the processor in the DAS-900 series was the VP-900. The first version (DAS-90) used 3/4″ U-Matic video cassettes while the second version (DAS-900) used either U-Matic of VHS video cassettes (the latter to obtain longer playing time). I have not been able to confirm if tapes made on the DAS-90 can play on the DAS-900 or not. Early input says they are compatible and should interchange.

The JVC DS-FC901 Interface Unit converted the consumer EIAJ (PCM-F1, etc., see below) signals into the professional JVC signals and vice versa. It took video in and out as well as digital in and out on a 50-pin Amphenol connector at TTL levels, 50 ohms! At least some field recordings were apparently made on this system. For sake of completeness, the following modules were part of this system: VP-900 Processor;RM-900 Remote Control; AE-900 Editor;DS-DM900 Digital Audio Mixer;TC-900 Time Code;DS-FC901 Digital Interface Unit; DS-SU900 Audio/Video Synchronizer. At this point, I do not know of any resources to transfer this format.

dbx developed the model 700 which was the first one-bit delta-sigma converter to be used in audio, predating the Sony system used on SACD. This system was used for wire/microwave transmission of the Boston Symphony summer concerts at Tanglewood to WGBH in Boston for broadcast. When recording, this was typically used with 3/4″ U-Matic video cassettes. Resources for Transfer: Safe Sound Archive/George Blood in Philadelphia, Pennsylvania

The most widely used system was the Sony PCM-F1 which was introduced in about 1982. The PCM-F1 and the SL-2000 lookalike BetaMax recorder made a portable system that could run off 12V. In addition to the PCM-F1, there were the PCM-501, PCM-601ES, and PCM-701 AC-operated processors from Sony and the PCM-100 from Nakamichi. The PCM-601ES had an SPDIF output on an RCA jack. All of these are interchangeable and we believe all PCM adapters from Japan (except the Sony and JVC professional systems mentioned above) are compatible as this was an EIAJ standard. Technics made a compatible one-piece, all-in-one unit that included the digital audio electronics and a VHS tape machine in one chassis.

In the EIAJ standard, both 14- and 16-bit operation was supported, although some units were 14 bit only. While Sony wished that the data be recorded on Betamax recorders, this data was also recorded on VHS and U-Matic recorders. In addition to recording, this data was also sent over a variety of video links.

While the F1/EIAJ format was intended for consumer use, it developed a small amount of traction in both consumer and professional circles, although market penetration was never great — probably much less than DAT. Many of the Grateful Dead concerts were recorded on this system by taping enthusiasts (which the band encouraged). For a while, NPR was using this equipment for time-zone delay. WGBH transmitted weekly audio broadcasts of the Boston Symphony in the PCM-F1 format using a local UHF TV channel so that Boston residents who had PCM-F1s could listen to  the  concerts  with the best possible fidelity.  Some of these transmissions were broadcast by PBS in other cities in the same manner. For at least one year the Christmas Eve service of Lessons and Carols from Kings College Cambridge was brought back to PBS and NPR via a PCM-F1 link on a second satellite video channel.

Resources for transfer: Richard L. Hess, Aurora, Ontario — Doug Pomeroy, New York — Bluefield Mastering, North Carolina — Ted Kendall, England

The above has focused on systems that use essentially unmodified video recorders to record bitstreams of digital audio which are made to look like a video signal in order to take advantage of the bandwidth of video recorders. Since the wide bandwidth of video recorders is in the luminance signal (and not the colour subcarriers) all of this information appears to have been carried only in the luminance channel.

To add to the confusion, there were dedicated formats that also used blank video tapes, but did not record in a video format. These are discussed here (link). Most notable of these were the Alesis ADAT which used S-VHS blank tapes and the TASCAM DTRS which used Hi-8 tapes.

Here is a summary of the possibilities of audio-on-videotape in addition to the normal use of both longitudinal and FM tracks for the sound that accompanied the video:

VHS Tapes:

  • Analog: HiFi audio (likely)
  • Adapter Digital: Sony PCM-F1 would be the most common, could be JVC DAS-900 or dbx 700
  • Dedicated Digital: Alesis ADAT (generally S-VHS tapes) 8-track
    Note that Technics had a one-piece PCM-F1 recorder.
  • Unknown: Akai 12-track

Betamax Tapes:

  • Analog: HiFi audio
  • Adapter Digital: Sony PCM-F1 (This was the default combination) could be dbx 700

Hi-8 Tapes:

  • Analog: HiFi audio
  • Digital on VCR: There was a digital audio mode, I believe, on this system
  • Adapter Digital: While possible, probably not likely
  • Dedicated Digital: TASCAM DTRS (DA-88, etc.) 8-track

U-Matic Tapes (3/4-inch):

  • Adapter Digital: Sony PCM 1610/1630, JVC DAS-90/900, dbx 700 are all likely; PCM-F1 is possible. The 1610/1630 format would probably be the most common.

Related Pages: Digital Audio Tape (includes open-reel tapes), Digital Audio on Disks

Thanks are due many people for their help with this page and especially the updates concerning the JVC system. I would like to thank the three who contributed the most to this: Tom Fine, Don Norwood, and Don Ososke.

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