Help! Audio Lag on 23.98 sequence

My audio is lagging on a 23.98 timebase sequence. Even if I create a new one, add no video, only audio (it's 17 min long) it lags behind its own waveform, noticeably after the 5 min mark and VERY noticeable after the 10 min mark.

If I create a 30p sequence, audio is fine and corresponds normally to its waveform.

It's definitely not the rate, because both sequence and file are 48khz.

What could I be doing wrong? Known bug?

OK, if this is not a nasty bug, I don't know what is.

Suppose I create a brand new sequence from scratch and add nothing but this audio clip, then I try the following steps, keeping every other setting but editing timebase:

- if editing timebase is set to 30, audio corresponds to waveform
- same for 29.97
- same for 25
- same for 24
- PROBLEM if it's 23.98. audio lags

FCP version is 7.0.2, OSX is 10.6.3

It's not clear to me from context what you mean by "lags." At first I thought you meant you were out of sync, but then you referred to putting down audio without picture? What's there to be out of sync with?

Jeff, with the waveform. Suppose you have a beep in the audio track, if you scrub over the waveform at the precise point, you'll hear the beep right? This works fine on all editing timebases but 23.98

This also means if I add video it's out of sync on 23.98.

You're saying the Waveform representing the sound doesn't line up with its occurrence through the speaker? Does it move the ballistics of the audio meter, such as a 2-pop peaking where it should on the waveform?

And only at 23.98? Bizarre. I wonder if recent versions have some extra processing in this format over 29.97... it could be a selective latency.

You may have discovered something wonderful... and annoying.

- Loren

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I've seen that. You play an audio clip in the Viewer and it's fine. The minute you stick it in a timeline, it changes positions, and waveforms no longer reflect what you're hearing.

I couldn't nail down the cause, either. Perhaps it's a corruption specific to certain batches of clips, similar to when a clip changes In/Out points after render. Or a combination of certain codecs and frame rates. (Yeah, that sounds thin to me too.) When it happened to me the most, I was working with Motion JPEG A clips.

Some Hail Mary ideas:

Re-export the audio by using a conversion program -- Compressor, QuickTime Player, Soundtrack etc.

Turn off audio renders; use only Audio Mixdown to render audio.


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