User Manual

AUDIO SYNC
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MIDI tracks, on the other hand, will always remain
continuously resolved to the incoming time code.
The discrepancy between MIDI and audio tracks is
caused by the fact that the audio tracks, after they
begin, resolve to the computer’s internal timing
hardware, not external time code. So, in essence,
there are two independent clock sources: external
time code and the computer’s internal clock. MIDI
is slaving to the external time code and audio is
slaving to the computer. The inevitable result of
two clocks running independently of each other is
that they will drift, no matter how accurate they
are. Practically speaking, the issue is: how long will
it take for them to noticeably drift apart?
When using the computer’s built-in audio, the time
it takes for MIDI and audio tracks to noticeably
drift apart depends on the accuracy of the time
code that Digital Performer is slaving to. If you
have an extremely accurate time code source, such
as a time code generator or other crystal clock-
based time code source, you might be able to play
MIDI and audio for minutes at a time with no
noticeable drift. If, however, the time code being
received is not accurate (such as time code from an
analog tape deck with its varispeed control
adjusted several percent high or low), you might
hear drift after only a few measures.
In most situations, you will probably be able to play
for at least several minutes without noticeable drift.
However, if you are using Digital Performer in a
professional situation, we strongly recommend
that you invest in a hardware-based digital audio
recording system that can be properly and
continuously resolved to time code as described
earlier in this chapter.
AUDIO SYSTEM CLOCK
If the audio hardware you are using with Digital
Performer doesn’t support multiple clock sources,
the Audio System Clock menu item (Setup menu)
will be grayed out. If your audio hardware does
support multiple clock sources, they appear in the
Audio System Clock sub-menu. The current clock
source is checked; to change it, choose another
clock source. Be sure to choose the correct clock
source for the situation in which you are running
Digital Performer. See your Digital Performer
manual for details. Using the proper clock source
will prevent clicks, pops, and other undesirable
artifacts during digital transfers. It will also ensure
that your digital audio is properly resolved with
external clock sources, such as SMPTE time code
or word clock.