DigiDesign DigiRack, Manual

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Chapter 6: DigiRack Real-Time TDM and RTAS Plug-ins 91
Using TimeAdjuster for Manual
Delay Compensation
DSP and host-based processing in all digital sys-
tems incurs delay of varying amounts. You can
use the TimeAdjuster TDM plug-in to apply an
exact number of samples of delay to the signal
path of a Pro Tools track to compensate for de-
lay incurred by specific plug-ins. TimeAdjuster
provides presets for common delay-compensa-
tion scenarios.
To compensate for several plug-ins in-line, use
the delay times from each settings file as refer-
ences, 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.
To manually compensate for DSP-induced de-
lays, try one of the following methods:
Phase Inversion
If you are working with phase-coherent track
pairs, or tracks recorded with multiple micro-
phones, you can invert the phase to negate the
delay. If you don’t hear any audio when you in-
vert a signal’s phase, you have precisely adjusted
and compensated for the delay. This is because
when you monitor duplicate signals and invert
the polarity (phase) of one of them, the signals
will be of opposite polarity and cancel each
other out. This technique is convenient for find-
ing 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, invert the phase.
4
Control-drag (Windows) or Command-drag
(Mac) to fine-tune delay in one sample incre-
ments, or use the up/down arrow keys to change
the delay one sample at a time until the audio
signal disappears.
5
Change 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 plug-ins display their delay values in
the channel delay indicators, this can be used as
another method for determining delay compen-
sation.
Some plug-ins (such as Digidesign’s Maxim
and DINR BNR) have different delays at
different sample rates. Refer to the Digide-
sign Plug-ins Guide for more information
about these plug-ins.
A delay table for DigiRack plug-ins appears
in Appendix B, “DSP Delays Incurred by
TDM Plug-ins.”