M-audio Biport 2x4s User Manual download pdf (Page 40)

At times, you may be given a tape with SMPTE already on it. The offset

time on the tape you receive will affect the start time that you set for

your MIDI sequencing. For example, if the time code on the tape starts at

02:00:00:00 (a 2-hour offset) and you need to start your sequence playing

3 minutes, 30 seconds into the work, you should set the sequencer start

time to 02:03:30:00.

Because MTC requires 8 quarter-frame messages to send a full frame of

time code, a minimum of 2 to 4 frames will be needed for a sequencer to

first sync up to a running SMPTE. Therefore, when syncing a MIDI

sequencer or any program to time code, it is a good idea to set your

sequence start time to a few seconds later than the offset of the time code

on tape. In other words, give your sequencer some time to acquire sync

and stabilize before it begins playing back. For example, if your tape

starting offset is 01:00:00:00, then set the sequence start time to

01:00:05:00, which is 5 seconds later. This is also known as a 5-second

pre-roll. Some sequencers will actually allow you to directly set the

“pre-roll” time to a specific number of seconds. These programs will

automatically sync up to an incoming MTC source for that pre-roll

amount, and then start playing.

Flywheeling

Due to the nature of magnetic tape, sometimes drop-outs occur on the

tape and leave gaps in the recorded time code. When a drop-out or other

media corruption occurs at the sync source and there is a resulting peri-

od of corrupted time code, the BiPort 2x4s continues to “flywheel,” out-

putting time code from the last properly received frame and increment-

ing at the proper frame rate. This flywheeling continues until valid time

code reappears on the BiPort 2x4s SMPTE input or until a preset time-

out occurs. The length of this time-out period is called the “Flywheel

Time.” The BiPort 2x4s flywheel time may be set to any amount from 1

to 255 frames, or infinite. It is good practice to use the shortest Flywheel

setting that will work with the amount of drop-out found on the media

you are syncing to. Infinite flywheeling is also known as Jam Sync and

may be used to continue generating time code long after the time code

source has expired.

Syncing to SMPTE

Recording a SMPTE Stripe (Writing SMPTE)

Before the BiPort 2x4s can be used to synchronize to a source audio

and/or video tape, that tape must be encoded with SMPTE time code.

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M-audio Biport 2x4s User Manual Page 40