35
User’s Guide
Another alternative is to use a common source of word clock for both the
DMTi
and the receiving device, assuming that the receiving device has an input for
it. Make sure that the receiving device is explicitly set up to sync to word
clock—this may be a hardware or software setting, depending on the design.
Make sure that whatever you are using as the master sync device is set to its
own internal clock. If every device in the chain is looking elsewhere for sync,
they will “hunt” each other, with the result that the system will be unstable,
creating noise or even failing completely.
Garbage
If the signal deteriorates into a harsh buzz, roar, or “hash” sound, it usually
means that clock sync has been lost. Check to see that the clock source you are
using is generating a valid signal. For example, you may have the
DMTi
’s clock
following the digital output of a DAT deck, as described above; when you turn
the deck off, the clock will go off, but the
DMTi
will continue trying to convert
incoming signals, with unfortunate results.
Pitch changes
These can occur when the wrong sample rate is chosen for a device. Examples:
• A sound file in Pro Tools or a tape on an MDM recorded at 48 kHz is played
back locked to an incoming sample rate of 44.1 kHz. The sound will play
approximately 8.8% slow (about 1
1
/
2
semitones flat).
• A recording on a DAT made at “low speed” (32 kHz sampling rate) is played
back using with a deck locked to an external 44.1 kHz signal. The recording
will play back approximately 37.8% fast (about 4
1
/
2
semitones sharp).
• A recording made on a video-based digital system using “pulldown” (i.e., a
frame rate of 29.97 fps) and a sample rate of 44.056 kHz, is dubbed to another
system nominally running at 44.1 kHz, using the source as the sync master.
When the dub is played back, it will be 0.1% fast (3.6 seconds per hour).
Most of these problems can be avoided by using the
DMTi
’s internal sample-
rate generator (i.e., setting
Clock Select
to
Int 44.1K
or
Int 48K
), and letting
the sources “free run”—that is, use their own internal clocks.