Setup guide

Appendix E: DSP-Induced Delays in Mixing 89
appendix e
DSP-Induced Delays in Mixing
This appendix provides an overview of DSP-in-
duced mixer delays, and explains how you can
compensate for these delays to improve time
and phase alignment of audio in complex or
critical mixing situations.
• To learn about DSP-induced delays and when
you should compensate, see “Introduction to
DSP-Induced Delay” on page 89.
• To learn how to compensate for delays auto-
matically with Delay Compensation
(Pro Tools HD only), see “Using Delay Com-
pensation” on page 90.
• For details on the sources of DSP-induced de-
lay, see “Delay Factors” on page 96.
Introduction to DSP-Induced
Delay
In all digital systems, DSP processing causes sig-
nal delays of varying amounts. These DSP-in-
duced delays can vary from as short as several
microseconds to as long as several milliseconds,
depending on the type of processing or routing
being performed.
Each plug-in, hardware insert, and mixer assign-
ment on a track delays that track by an amount
equal to the total of all DSP-delay factors. (For
more information on these delays, see “Delay
Factors” on page 96.)
In some cases, signal processing delays matter
only if you use a real-time TDM plug-in on one
channel of a stereo or multichannel signal but
not the others. This imparts an unequal amount
of delay to the signals on that channel, which
subsequently may cause undesirable cancella-
tion of certain frequencies.
In simple terms, DSP-induced delay can cause
audio to arrive at the main output (or a submix
output) at different times. To maintain time
alignment, you can compensate for DSP-induced
delays.
When to Compensate
You may only really need to compensate for de-
lays between tracks where phase coherency
must be maintained (as with instruments re-
corded with multiple microphones or stereo
pairs). If you are working with mono signals,
and the accumulated delays are small (just a few
samples, for example), you probably do not
need to worry about compensating for delays.
Do not confuse signal processing-induced
delays with monitoring latency or time do-
main effects processing (such as delay, echo,
reverb, and other desirable delay effects).
Audible symptoms of phase issues include
comb-filtering and loss of high frequencies.