Synchronization - MOTU MIDI Timepiece AV User Manual

Figure 15-1: Converting time code. When your Express interface
converts incoming time code, the red TACH light blinks, the green
LOCK light glows steadily, and the green computer OUT light glows
steadily as well. For the micro express, the lights on the front panel
are arranged slightly differently than what is show here on the XT, but
they perform in an identical fashion.
If the LOCK and TACH lights do not behave as
described, your Express interface is not
successfully locking to the SMPTE time code. This
could be a problem with the audio connections
between the tape deck and your Express interface.
It could also be that the SMPTE level is not high
enough. See Appendix C, "Troubleshooting and
Customer Support" page (173).
If the LOCK and TACH lights look OK, but the
green computer OUT LED is not glowing, this
means that your Express interface settings have
been altered somehow such that it is not sending
MIDI time code to the computer. To correct the
settings, see Figure 7-15 on page 50.
Getting a running update of SMPTE
You can get a running update of SMPTE in the
ClockWorks SMPTE Reader and Sync/MMC
windows. For details, see chapter 10, "Sync and
MIDI Machine Control" (page 59).
SMPTE Offset
When reading time code, there may be times when
you need to offset your Express interface a certain
amount from the time code you are feeding it. See
Figure 10-3 on page 60 for details.
92
Red TACH light
Green
Green
computer OUT
LOCK light
light
Routing MIDI Time Code to other devices
At times, you may need to route MIDI Time Code
to a device connected to one of your Express
interface's MIDI OUTs. Similarly, you may have the
need to route MTC to serial port B on your Express
interface. For example, serial port B might be
connected to a Macintosh, which you need to slave
to time code. To make time code routings such as
these, see "The MTC In and MTC Out
connections" on page 49.
Freewheeling to avoid time code dropouts
When your Express interface encounters a drop-
out —a series of missing or unreadable frames—in
the SMPTE time code, it "freewheels" past them,
pretending that they were not missing by briefly
generating its own code to make up for the missing
frames. The default freewheel value is 4 frames.
This means that your Express interface will
continue to generate time code for four more
frames after it stops receiving time code. If it does
not receive any more time code after four frames, it
will stop converting.
The factory default base setups have the
freewheeling feature set to 4 frames for fastest
response when you stop the tape deck. The
Freewheel amount can be adjusted up to 32 frames.
This allows your Express interface to maintain
lockup even over lengthy SMPTE drop outs.
If you encounter a time code drop out that causes
your Express interface to stop converting for a
moment, try increasing the freewheel amount in
the Sync/MMC window. Try adding just a few
frames at a time when adjusting the amount. (For
details on the "one time jam sync" option, see
"Regenerating fresh time code ('jam syncing')" on
page 95.)
your Express interface freewheels at the frame rate
it is reading at the time it begins freewheeling —
except for 29.97 drop and non-drop. If you intend
S Y N C H R O N I Z A T I O N