[ardour-dev] Re: MTC & MMC ...
thirdoption at hotmail.com
Wed Sep 22 17:41:15 PDT 2004
> > For some reason I have
> > to set the Tape Offset in Seq+ to a value > 0 before it will behave
> > correctly: does anyone know why that's so ?
> this is just always so about the offset. i've always had my cakewalk set
> offset to :03 seconds when I sync to darwin. it's just because it takes a
> second for the sequencer to catch the stream.
here's a more technical explanation of why this is:
But the Quarter Frame is more than just a quarter frame "clock tick". The
Quarter Frame message's data byte contains the SMPTE time (ie, hours,
minutes, seconds, and frames). SMPTE time is normally expressed in 80 bits.
Obviously, this is too many bits to be contained in 1 8-bit data byte. So,
each Quarter Frame message contains just one piece of the time (for example,
one Quarter Frame may contain only the hours). In order to get the entire
SMPTE time at any given point, a slave needs to receive several Quarter
Frame messages, and piece the current SMPTE time together from those
messages. It takes 8 Quarter Frame messages to convey the current SMPTE
time. In other words, by the time that a slave can piece together the
current SMPTE time, two SMPTE frames have passed (ie, since there are 4
Quarter Frame messages in each frame). So, MTC's version of SMPTE time
actually counts in increments of 2 SMPTE Frames per each update of the
current SMPTE time.
-- from http://www.borg.com/~jglatt/tech/mtc.htm
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