MOTU micro express-USB, Руководство пользователя

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S M P T E S Y N C H R O N I Z A T I O N
74
Take care after using the offset/start time
The LTC Start setting in the Express interface
serves as the start frame when striping, but also as
the offset when reading. If you stripe at 1 hour
(1:00:00/00) and then lock to the time code you
just striped — without readjusting the offset/stripe
setting back to zero (0:00:00/00), then the
Express interface converts starting at 2 hours
(2:00:00/00).
Striping SMPTE on a multitrack tape deck
The goal when striping SMPTE time code is to
generate an error-free signal strong enough for
reliable lockup, but not so strong that the SMPTE
bleeds through to adjacent tracks.
There are several ways to handle this. One way is to
leave an empty track on your multi-track tape deck
as a buffer between the SMPTE and other tracks.
With a buffer track, SMPTE can be recorded at
very strong (“hot”) levels (above 0 VU) without
risk of bleedthrough.
If your tape deck has no tracks to spare, a good
level at which to record is around –3 VU. That is,
the VU meter for the SMPTE track on your tape
deck should read –3 when you stripe the SMPTE.
This records SMPTE that is hot enough for reliable
lockup and weak enough so that it will not bleed
into adjacent tracks. -3 VU is only a rule of thumb,
though, so don’t hesitate to use other levels if they
work better for you.
LTC MODE
In LTC mode, your Express interface locks to
incoming SMPTE time code received on its
SMPTE IN jack. But LTC mode differs from LTC
QuikLock mode in several significant ways. In LTC
mode, your Express interface:
■
Emits regenerated LTC on its SMPTE OUT jack
■
Analyzes incoming time code and responds in
several useful ways, depending on what happens to
the incoming time code
■
Measures incoming time code with an extremely
accurate internal clock to see how fast or slow it is
running and displays the results in the SMPTE
Reader window in Express Console
Because LTC mode employs a sophisticated phase-
lock synchronization engine in your Express
interface, the amount of time it takes to establish
lockup to incoming time code is considerably
longer than LTC QuikLock mode. On the other
hand, LTC mode offers the additional capabilities
mentioned above. These features, and how you can
use them, are discussed in the next few sections.
Regenerating fresh time code (‘jam syncing’)
SMPTE is a problem when you are copying tapes: it
degrades rapidly every time you try to copy it from
one tape to another. Often, the SMPTE signal
deteriorates so much that it will not be
recognizable by any SMPTE-to-MIDI converter,
including your Express interface, and you will no
longer be able to lock to it.
The solution to this problem is to use your Express
interface to regenerate fresh SMPTE time code that
matches the original time code while you are
copying the tape. Some people refer to this process
as
jam syncing . When your Express interface
receives a SMPTE signal on its SMPTE IN cable, it
always regenerates a fresh signal that exactly
matches the incoming signal and sends it out the
SMPTE OUT cable (except for drop-outs, which it
eliminates with freewheeling).
!USB Interfaces Manual Book Page 74 Tuesday, October 10, 2000 12:43 PM