Here is the recipe, to clarify, so that it might help others:
To tempo adjust a, say, a 127 bpm (even when it drifts and varies slightly) audio file to a 125 bpm project:
- Import the audio file / drag to an empty track.
- Select it and choose Project → Tempo Detection…
- Change that first time signature marker that gets created from its default 1/4 to 4/4 (if appropriate).
4) Temporarily change every other track in the project from Musical time base to Linear time base. - Select the audio file track and choose Audio → Advanced → Set Definition from Tempo…
- Deactivate that new Tempo Track and/or delete all the events on it and set it to the original (or desired) tempo.
- Change all the tracks back to Musical time base (as appropriate).
The imported audio file should now lock to the tempo (as well as all the other tracks).
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