Tach pulse

A signal generated by the tachometer roller of an audio or video transport, one or more times per rotation. Because the tach roller is in contact with the tape in fast-wind modes as well as play or record mode, it can be used to get approximate tape location data when SMPTE timecode data cannot be read. Tach pulses sent by various decks to the synchronizer allow it to stop each deck near the SMPTE timecode designated by the engineer. Once in play or record modes, the decks will again interlock via the SMPTE timecode data. Tach pulses do not include location information, only speed and direction. Tach pulse is the mechanical, or analog, equivalent of word clock. See also bi-phase/tach.

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