Video as a Clock Master

Bob Katz Leave a Comment

From: Clifford Britto

Hi Bob,
I was reading your articles on recording & compression . The section on digital recorders & DAW is really interesting . I have a question, hope you can clear it for me. If a wordclock signal depends on the sampling frequency, what happens when one uses Video as the clock master? How can you change the pitch of the recorded audio signal , of , say a tascam DA-88 recorder in the digital chain?

Good question. In many cases, the tape machine that has varipitch has to be the master, or independent. First of all, only if you take the analog output of these machines can you take advantage of varipitch anyway. The reason is if you are taking the digital output and you slow them down or speed them up, the following device in the chain will still lock to the samples…. You may even hear it slowed down or speed up, but as soon as you record it, and then play it back, the original pitch returns, as you are then playing it back at the correct sample rate.

Varipitch in the digital domain requires a sample rate converter between the source tape machine and the following recorder. You would have to “release” the source machine from video or word clock in order to run it at a different speed. Another alternative is to use a software pitch converter like the TC Electronics System 6000, which changes pitch but remains at (for example) 44.1 k in and out. The System 6000 uses intelligent splicing algorithms to accomplish the pitch shift. It solves a lot of problems…

Hope this helps,

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