Audio Tracks Out of Sync?!

Question

I opened up one of my projects today and started playback and everything was all over the place, out of sync.
the project consists of acoustic guitar, electric guitar and two vocal audio tracks plus a b4 organ track and an ultrabeat drum track.
i shuffled things around to get them back to normal, moving my audio regions around a bit until it sounded right. i ended up messing pretty much everything up so i used the command to move all audio regions to original location.
the drums were still out of sync and off tempo, even. i wondered if i had messed with the tempo and not remembered so i started playing with it trying to get it to match.
i quickly discovered that if i adjust the tempo at all, my audio tracks/ regions fall out of sync again. this makes no sense to me whatsoever, and i'm kind of worried i may have a corrupt project or something.
does anyone know what this may be and how to fix it????? thanks.

Answer 1

X-man is correct. This behavior isn't unique to Logic either.
Let's say your sequence is at 60 BPM. That's 1 beat every second. You record 4 tracks, each with an individual hit of a drum and nothing else:
Track 1: Kick on beat 1 - heard at zero seconds
Track 2: Snare on beat 2 - heard at 1 second
Track 3: Kick on beat 3 - heard at 2 seconds
Track 4: Snare on beat 4 - heard at 3 seconds
Now you change the tempo to 120 BPM. That's 1 beat every 1/2 second. Because you've got these individual sounds recorded on separate tracks, their playback will occur more quickly. In fact, twice as fast:
Track 1: Kick on beat 1 - heard at zero seconds
Track 2: Snare on beat 2 - heard at 1/2 second
Track 3: Kick on beat 3 - heard at 1 second
Track 4: Snare on beat 4 - heard at 1 1/2 seconds
This is not time compression. Changing the tempo from 60 to 120 simply causes the individual recordings to play back sooner relative to bar 1/beat1. In this case, half as much time elapses between the playback of each sound.
IT'S A WHOLE DIFFERENT STORY if this kick/snare pattern is contained in a single audio recording, because the spacing of the kicks and snares is frozen in time within the recording.
Let's say you record kick/snare/kick/snare as a single piece of audio at 60 BPM...
a) if the recording is made at bar 1/beat 1, no matter what the tempo of the sequence is changed to at a later time, this recording will be always be 'anchored' at bar 1 beat 1.
b) if the recording was made at bar 4/beat 1 (that's 4 seconds in from bar 1, beat 1) and then you change the tempo to 120 BPM, the timing of the drum sounds in the recording won't move relative to one another, but what will move is WHEN IN TIME that recording is triggered to play back. In this case, doubling the tempo is going to make that region trigger still play back on bar 4, but you get to bar 4 twice as fast at 120 BPM than you do at 60 BPM!! So the region will play back after 2 seconds have elapsed (from bar 1).
HOW TO GET AROUND THIS:
There's a key command called "Lock Regions to SMPTE Postion" (do a search for "SMPTE" or "Lock" in the key commands window). When you select regions and apply this command they'll be locked at the time of their original recording. This way you could record tracks that don't all start together, like this:
XXXXXXXXXXXXXXXX
            YYYYYYYYYYYYYYYYYYYYYY
      ZZZZZZZZZZZZZ
...then change the tempo at a later time but NOT have the tempo change affect the position of the regions relative to one another.