5.5.7 Common Systems and Characteristics: Video Tape Based Formats
5.5.7.1 There are two variants within this category: systems using videotape in a standard VCR to record digital audio encoded on a standard video signal, and systems using videotape as the storage medium for proprietary digital audio signal formats.
5.5.7.2 Sony has produced a range of formats using VCR systems as a high bandwidth storage device. More recently Alesis introduced the ADAT system, which used S-VHS videocassettes as high capacity storage media for their proprietary format of digital audio, and Tascam released the DTRS system using Hi8 videocassettes as the storage medium.
5.5.7.3 Formats using video recorders were based on interface devices that incorporated A-D and D-A converters, audio controls and metering, and the hardware required to encode the digital bit stream as a video waveform. Sony’s professional system specified NTSC standard (525/60) Black-and-White U-Matic VCR, and these were manufactured specifically for digital audio use. The semi-professional PCM-F1, 501 and 701 series worked best with Sony Betamax recorders, but were generally compatible with Beta and VHS. Machines in this series supported PAL, NTSC and SECAM standards.
5.5.7.4 Reproduction of VCR based recordings requires availability of a VCR of the correct standard, plus the appropriate proprietary interface. There is normally backwards compatibility within related systems, so purchase of later generation equipment should facilitate replay of the widest range of source material. As some of the video based PCM adaptors had only one A/D converter for both stereo channels, there is a time delay between the two channels.When the tapes are replayed and the audio data is extracted the signal processor delay should be corrected in the digital domain. Transfers should be made only with equipment which allows the output of a digital signal.
5.5.7.5 Early digital recorders sometimes encoded in what are now uncommon sampling rates, such as 44.056kHz (see table 4 Section 5.5). It is recommended that the resultant files be stored at the encoding levels at which they were created. Care should be taken to ensure that automatic systems do not misrecognise the actual sampling rate (eg a 44.056kHz audio stream may be recognised as 44.1kHz, which alters the pitch and speed of the original audio). Second files can be created for users in common sampling rates using appropriate sampling rate conversion software. Nonetheless, the original file should be retained.
5.5.7.6 In addition, third-party equipment for systems based on domestic VCRs can provide useful extended functionality, including better metering and error monitoring facilities and professional inputs and outputs.
5.5.7.7 VCR based systems are obsolete, and equipment will need to be sourced second-hand.
| Format | Variants | Carrier Type | Audio and data tracks | Digital Audio Standards supported | Interface |
|---|---|---|---|---|---|
| EIAJ Sony PCM-F1 PCM-501 and PCM-701 systems | Video signal may be PAL, NTSC or SECAM | Domestic VCR — normally Betamax or VHS cassette Rare examples use ½” open reel videotape | Stereo Audio | 14 bit standard, Sony hardware allows 16 bit sampling (with less error correction) 44.056 kHz in NTSC systems, 44.1 kHz in PAL systems | Analogue line in and out standard. Digital I/O capability with third party add-ons |
| Sony PCM1600 PCM1610 and PCM1630 | U-Matic – Black and White, 525/60 (NTSC) | Stereo audio plus Compact Disc PQ codes Timecode on U-matic linear audio track | 16 bit 44.1 kHz | Sony proprietary system. Digital audio on separate Left and Right Channels plus word-clock | |
| DTRS (1991) | Proprietary format on Hi8 video cassettes | 16 bit 48 kHz 20 bit recording optional on some systems | SP-DIF or AES/ EBU | ||
| ADAT (1993) | Proprietary system on S-VHS cassettes | SP-DIF or AES/ EBU |
Table 4 section 5.5 Digital Audio on Videotape – Common Systems
