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Digidesign Universal Slave Driver

Synchroniser By Mike Collins
Published January 1998

Digidesign Universal Slave Driver

Digital devices need synchronisation just as much as analogue ones, and this new offering from Digidesign aims to be a one‑box solution for most audio and visual sync requirements. Mike Collins says it's about time...

All digital audio systems, whether workstations like Digidesign's Pro Tools, mixers like the Yamaha 02R, or outboard like the Lexicon PCM90, have internal quartz crystal oscillators which control the speed of the digital audio playback or recording — just as the motors in analogue tape machines control the speed of the tapes. If you want to link two or more analogue tape machines together and have them play back or record in sync with each other, you need a machine synchroniser which will control the speeds of the motors on the analogue machines to keep them in step. The machine synchroniser typically reads SMPTE timecode and 'tach' pulses coming from each machine, compares these with the synchroniser's internal clock or with an external clock feeding the synchroniser, and speeds up or slows down the motors of the analogue machines accordingly. SMPTE timecode is also used to provide location information, so that locate points can be entered into the synchroniser and the machines will wind forward or backwards to the correct points. Some of you may have come across 48‑track recording systems in professional studios, where two 24‑track tape machines are linked and controlled in this way, while others may be more familiar with linking a Sony U‑Matic VCR with a Fostex B16 multitrack tape recorder to put music to picture.

What you may not have fully realised is that when you connect digital audio systems together, their clocks need to be synchronised too — even if they are mixers or other outboard devices. Digital audio signals are similar in some respects to video signals, in that they carry sync information within the signal. So, whether you connect your digital devices using S/PDIF, AES/EBU or ADAT optical connectors, sync information will be available which the receiving device can 'lock' to. Most professional digital devices will also have a separate sync connection, which would be a so‑called 'wordclock' signal via BNC connectors for most equipment, a Digidesign 'Super Clock' (wordclock x 256) in the case of Digidesign equipment, or possibly an AES/EBU sync signal via XLR. Another option...

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Published January 1998