DigiDesign Digidesign Pro Tools 8.0, Reference Manual

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Pro Tools Reference Guide 18
Tick-Based and Sample-Based
Time
Pro Tools lets you set any track timebase to
either sample-based or tick-based. You can also
set the Timeline to be viewed as tick-based or
sample-based.
Audio in Pro Tools is sample-based by default.
This means that if an audio region is located at a
particular sample location, it will not move
from that location if the tempo changes in the
session—though its Bar|Beat location
will
change.
MIDI data in Pro Tools is tick-based by default.
This means that if a MIDI region is located at a
particular Bar|Beat location, it will not move
from that Bar|Beat location if the tempo changes
in the session—though its sample location
will
change.
You can select whether a track is sample-based
or tick-based when it is created, or change time-
bases later.
Sample-Based Audio and MIDI
With a sample-based audio track, all regions in
the track have an absolute location on the Time-
line. Regions stay fixed to the sample time, re-
gardless of where tempo or meter changes occur
in a session.
If you make a MIDI track sample-based, all MIDI
events in the track have an absolute location on
the Timeline. MIDI events stay fixed to sample
time, regardless of any tempo or meter changes
in a session.
Tick-Based Audio and MIDI
Tick-based audio is fixed to a Bars|Beat location,
and moves relative to the sample Timeline when
tempo and meter changes occur. However, MIDI
events and tick-based audio respond differently
to tempo changes with respect to duration.
MIDI note events change length when tempo or
meter is adjusted, while audio regions do not
(unless Elastic Audio is enabled). When Elastic
Audio is
not enabled on an audio track, meter
and tempo changes affect only the start point
(or sync point) for each audio region in a tick-
based track. If Elastic Audio is enabled on an au-
dio track, tempo changes apply Elastic Audio
processing, which changes the duration of the
audio region.
Elastic Audio
Elastic Audio provides real-time and non-real-
time (rendered) Time Compression and Expan-
sion (TCE) of audio. Tick-based Elastic Audio
tracks actually change the location of samples
according to changes in tempo. The audio
stretches or compresses to match changes in
tempo. Elastic Audio also provides high-quality
non-real-time region-based pitch shifting.
Pro Tools Elastic Audio uses exceptionally high-
quality transient detection algorithms, beat and
tempo analysis, and real-time or rendered TCE
processing algorithms. Elastic Audio lets you
quickly and easily tempo conform and beat
match audio to the session’s Tempo ruler. It also
provides an unprecedented degree of control
over transient detection and TCE processing on
an event-by-event basis.