Arranging : Time, Tempo, Meter, Key, and Chords : Tick- and Sample-Based Timebases : Tick-Based Audio and MIDI

Tick-Based Audio and MIDI
Tick-based audio is fixed to the relative time of the Bars|Beats Timebase ruler, and moves relative to the sample Timeline when tempo and meter changes occur. However, MIDI and Elastic Audio events, and tick-based audio clips (non–Elastic Audio) respond differently to tempo changes in respect to duration. MIDI note events and Elastic Audio clips change their duration when tempo is adjusted, while non–Elastic Audio audio clips do not. Tempo changes affect only the location of the beginning (or sync point) of each audio clip in a tick-based (non–Elastic Audio) audio track.
You can select whether a track is sample-based or tick-based when it is created, or change timebases later.
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To have all new tracks default to tick-based, enable the New Tracks Default to Tick Timebase option in the Editing Preferences.