sync trouble after rec with tempo changes

SnackDaddy · Post by **SnackDaddy** » Mon Jul 26, 2004 6:28 pm

Hi,

I'm trying to use Live in Session View to record loops while it's synced to an external sync master via midi clocks. Everything works fine until I change tempo while recording. After I finish recording the loop, it does not sync up correctly in playback.

I tested with a straight forward setup:
- input was audio beat clicks on every quarter note at 100bpm coming from "Program A" which was sync master
- recorded for several measures
- Program A then speeds up by one BPM every beat, up to 130bpm. So, over 30 beats, the tempo changed steadily from 100bpm to 130bpm.
- continued to play and record the clicks at 130bpm for a few more measures
- while all this is happening the Live metronome is playing and keeping sync with the incoming audio beat clicks, even while tempo is changing (although, Live seems to average midi clocks over approx 2 beats, so the tempo changes lag just slightly)

When I play this loop back in Live, the sync starts to get off as soon as the part comes where the tempo was changing. By the end, Live is off by a full 1/8th note.

Here's my guess as to what is happening - after Live has recorded the loop, it puts it through the standard module for finding warp markers, and is assuming that the loop was played at a steady tempo. Since it wasn't played at a steady tempo, it gets it wrong.

BUT, since Live was following the tempo and the beat as it was recording, it could in fact set the warp markers correctly if it tracked the tempo changes during recording and used them to determine the warp markers while the loop was being recorded, or when recording was done - that would seem (relatively!) straight forward. Warp markers ought to be pretty trivial to setup when the tempo is known at every moment.

This would be a great help to me (and others?), since I like to do live sampling of other musicians while we play and the tempo is changing. Currently I have to be sure to only do live sampling when I know the tempo is fixed, so I don't run into this problem.

Cheers,
Michael