How do digital recorders handle selective synchronization?
Selective Synchronization, or “Sel-Sync” as it is often called, is the ability of a recorder to play and record simultaneously, allowing synchronous recording of new material onto specific tracks without erasing everything on tape. This technique is what makes overdubbing possible. On an analog recorder, audio tracks are discrete entities, and the sync head is really just a stack of individual heads, any one of which is capable of recording or playing back. Thus sel-sync is a relatively simple matter of putting some heads into record and others into repro. In the digital world, the problem is highly complex. First, A/D and D/A conversion involves an acquisition delay of several milliseconds. Second, and more importantly, digital tracks are not discrete. Rather, they are multiplexed together on a tape, along with subcode and other non-audio information. So how can you replace one track and leave the others untouched? The answer is a technique called “read before write” (RBW) or “read, m
