5.1 DigiRack Plug-Ins Guide - Digidesign Support Archives

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Using TimeAdjuster for Delay
Compensation
DSP processing in all digital systems incurs delay
of varying amounts. You can use the Time-
Adjuster TDM plug-in to apply an exact number
of samples of delay to the signal path of a
Pro Tools track to compensate for delay incurred
by specific plug-ins. TimeAdjuster provides presets
for common delay-compensation scenarios.
To compensate for several plug-ins in-line, use
the delay times from each settings file as references,
and add them together to derive the total
delay time.
Alternatively, look up the delay in samples for
the plug-ins you want to compensate for, then
apply the appropriate amount of delay.
A delay table for DigiRack plug-ins appears
in Appendix B, “DSP Delays Incurred by
TDM Plug-Ins.”
To compensate for DSP-induced delays, try one
of the following methods:
Phase Inversion
If you are working with phase-coherent track
pairs, or tracks recorded with multiple microphones,
you can use a common studio technique
to null out the delay. Flop the phase of
the target track using the TimeAdjuster plug-in’s
Phase Invert button, and adjust the plug-in’s delay
time until the signal disappears. Then disengage
the Phase Invert button.
If you don’t hear any audio when you flop a signal’s
phase, you have precisely adjusted and
compensated for the delay. This is because when
you monitor duplicate signals and invert the po-
DigiRack Plug-Ins Guide
larity (phase) of one of them, the signals will be
of opposite polarity and cancel each other out.
This method is convenient for finding the exact
delay setting for any plug-in.
To determine the delay of a plug-in by inverting its
signal phase:
1 Place duplicate audio regions on two different
audio tracks and pan them to the center
(mono).
2 Apply the plug-in whose delay you want to
calculate to the first track, and a Time Adjuster
plug-in to the second track.
3 With TimeAdjuster, reverse the phase.
4 Command-drag (Macintosh) or Control-drag
(Windows) to fine-tune delay in one sample increments,
or use the up/down arrow keys to
change the delay one sample at a time until the
audio signal disappears.
5 Flop the polarity back to normal.
6 Save the TimeAdjuster setting for later use.
Comb-Filter Effect Cancellation
Adjust the delay with the signal in phase until
any comb-filter effects cancel out.
Viewing Channel Delay
Because TDM plug-ins display their delay values
in the Mix window’s channel delay indicators,
there is a third method for determining delay
compensation, performed as follows.