Speed up fail vs audio sync

Hi all. I've cut together some video footage of a live music performance from various different cameras and takes, all is nicely in sync with the audio that was recorded separately at the time and has been imported and it all lines up well. It's about 7 minutes long...and it's all a bit slow.  I've sped up the music in Logic a bit, and it sounds great. I've exported the video, and reimported to a new project, then imported the faster music. I've made sure that they both start at the same point, and tried to speed up the video so that the loud final note of the music on the original video lines up with the end note of the new music.  To fit, it comes out at 107%. BUT...when I play it back the music is in sync for about the last 30 seconds only - everything in the 6.5 minutes before is way out of sync.  What am I doing wrong!? If I put markers at key moments in the video new audio they will never seem to line up. Thanks everyone.

Rather than trying to do this separately, audio then video, I would combine the video and audio into a compound clip and speed up the compound.

Thank you, Tom. Yes, I tried this, and it's in sync with itself - but the audio degrades as a result. The music software is good for speeding up audio, FCP is good for speeding up video! Perhaps I'll have to start again and retime individual clips to the faster audio.  Or import the faster video to the music software and try and time the music to it...?

CRS wrote: I've sped up the music in Logic a bit...exported the video, and reimported to a new project, then imported the faster music... both start at the same point...tried to speed up the video so that the loud final note of the music on the original video lines up with the end note of the new music.  To fit, it comes out at 107%. BUT...when I play it back the music is in sync for about the last 30 seconds only - everything in the 6.5 minutes before is way out of sync...

I tested a similar scenario but exported full-duration audio and changed the audio speed externally with Audacity to 107%. After re-import of that and changing the exported/imported A/V timeline to 107% in FCP, both audio tracks were in sync.

Do you have any mixed-frame-rate video clips in the project, or clips which do not match the project frame rate?  especially, 23.98 and 25 fps?  I wonder if FCP did rate conforming on that before the export, which could have selectively changed the duration of the non-matching clips. 

PluralEyes can do continuous sync drift correction, whereas FCP audio sync only picks a single sync point (just like you'd do it manually). However give your description, I don't understand why it's out of sync.

I also don't understand why audio would degrade if retimed in FCP vs Logic. I've never seen that reported before. FCP handles the 32-bit floating point files from our Sound Devices recorders, but we usually don't retime that. I think Logic has more sophisticated and tunable pitch correction than FCP, so I suppose retimed audio could sound different between the two apps.

When you go to Logic, it wants to natively make all audio 44.1kHz. Change the project settings so it works with 48kHz audio, which is standard video. If you take 44.1kHz back into FCP, the of that audio will be off.

I find I can re-time audio (depending on content) in FCP +/- 5-7% max before it sounds unnatural. Some audio I can't push that far. If you say the quality of the audio degrades, export it and test it.

I'd try retiming in Compressor, too.

That's so helpful, thank you.  I'll go back and check everything and work through your suggestions. I really appreciate the advice.