Dbx Model 700 Digital Audio Processor

The dbx Model 700 Digital Audio Processor was a professional audio ADC/DAC combination unit, which digitized a stereo analog audio input into a bitstream, which was then encoded and encapsulated in an analog composite video signal, for recording to tape using a VCR as a transport. Unlike other similar pieces of equipment like the Sony PCM-F1, the Model 700 used a technique called Companded Predictive Delta Modulation, rather than the now-common pulse-code modulation. At the time of its introduction in the mid-1980s the device was the first commercial product to use this method, although it had been proposed in the 1960s and prototyped in the late '70s.

Unlike the many digital recording formats that would follow (e.g. DAT and ADAT), the Model 700 had no capability for storage on its own, and relied on an analog recording medium supplied by the user. In general, any high-quality VHS VCR would do, although 3/4" U-matic or Beta decks could also have been used. If viewed on a monitor, the output stream of a Model 700 looked like analog TV "static" or noise, with slight black bars running down either side.

Early on, the machine was hailed as "the best recording device you can buy," and Stereophile Magazine reviewed it positively. Many people liked the format because it offered more dynamic range than analog tape, but without the "hard clipping" inherent in PCM audio recorders of the time. The Model 700 had been designed from the beginning to have many 'tape-like' characteristics, including "soft saturation," and at a time when most professional and amateur recordists were used to analog tape, this was considered a significant feature. It also offered 14dB more dynamic range than 44.1kHz/16b audio, and because of its very high sample rate (644kHz), it did not contain the same anti-aliasing filters necessary in PCM recorders at the time, which were thought to cause undesirable harmonic interference.

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