Fons Adriaensen wrote:
Locating (while stopped) is a remote control function,
which
is not the same as syncing. SMPTE in itself does not support
anything similar to a locate command, it's not a remote control
protocol but just an audio signal that can be decoded to time.
SMPTE was developed as a way to sync audio (on magnetic tape)
to optical film, and later to video. It was also used to sync
audio tape machines, e.g. two 24-tracks recorders, to each other.
In all cases the essential trick was to record it on tape as an
audio track, thereby creating a time reference that was physically
bound to the real audio tracks on the same tape. Sort of 'soft'
sprocket holes, with the extra that each such hole also was also
labeled with its number.
Most machines supporting SMPTE sync would also support locating,
by combining conventional mechanical tape motion sensing with
the timecode system, and in the sense that when the master started
rolling the slaves would chase to approximately the same location,
then start rolling, then sync accurately. This latter could take
some seconds, but once sync was established it could be very
accurate, actually better than a sample at 48 Khz.
Ciao,
For decades it was used to sync several VTRs by a computers cut list, to
cut videos and I guess it's still not outdated. Yes, it's very accurate
(IIRC the precursor of SMPTE was invented for the NASA Apollo missions).
I guess a noticeable pre-roll only will occur when tape recorders need
to reach speed, but I don't think noticeable pre-roll is needed for hard
disks. The big exception for a long delay is film cut, when several
machines have immense offsets because of cuts and the machines need to wind.
Ralf