Solving Audio Sync Drift

Posted on by Larry

Recently, I received a number of emails from folks with problems with audio that slowly drifts out of sync. These complaints cover Final Cut Pro X, Final Cut Pro 7, and Compressor.

Sync drift is generally caused by audio sample rates that don’t properly match the audio settings in the sequence. Here’s an article that explains this.

www.larryjordan.com/solving-problems-caused-by-audio-sample-rates-that-dont-match/

However, there are also problems with ProRes HQ and how it handles audio sync. Take a look at the two comments at the end of this article for more information:

www.larryjordan.com/fixing-out-of-syncsound-in-a-prores-file/

But in the cases this week, the audio sync problem was caused by trying to edit an MP3 audio file. MP3 is extremely compressed and often difficult to edit. I strongly recommend converting (or transcoding) any MP3 files that you need to edit into AIF before you start editing. This won’t improve the quality, but it will simplify your editing. And the good news is that this conversion process is very fast and can be automated.

NOTE: Soundtrack Pro just hates editing MP3 audio – transcoding (or conversion) is almost mandatory.

Here’s how to convert your MP3, or any other audio format, to AIF using Compressor. (I’m using Compressor 4 for this example, but the process is the same using Compressor 3.x.)

1. Open Compressor.

2. Click Add File in the top left corner and import the MP3 file(s) you want to convert.

3. Click the Settings tab, twirl down the Apple folder, twirl down Audio Formats and look for the AIFF File setting.

4. Drag the AIFF File setting on top of the task that contains your audio file in the top window.

5. Look in the Inspector and make SURE the sample rate is set to 48.000 kHz. This is the default setting for recording audio with video. If the sample rate is correct, go to Step 10. If it isn’t, go to Step 6.

6. Click the Encoder button at the top of the Inspector.

7. If the automatic sensor button is dark, as it is here, click it to turn it off.

8. If the clip is mono, set the Channel layout to Mono. If it is Stereo, set Channel layout to Stereo.

9. Change the Sample rate popup menu to 48000.

10. In the task bar at the top, make sure the Destination (middle column) is set and you’ve given the compressed file a name (right column). Then, click Submit in the lower-right corner.

11. In the next dialog, click Submit and your file is sent off to be converted. Converting audio files is VERY fast, so even if you have a lot of MP3 files to convert, you won’t be wasting a lot of time.

NOTE: Once you have a setting you like, turn it into a Compressor droplet which automates the entire audio transcoding workflow. This article explains how. www.larryjordan.com/technique-creating-a-compressor-droplet/


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73 Responses to Solving Audio Sync Drift

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  1. Iain Davidson says:

    Hi Larry – thanks for ths tip – I’ve been tearing my hair out for days wondering why an audio commentary kept losing sync with the video. It was recorded at 44.1 kHz.

    Now I’ve converted it from .aiff to .aiff, but with the correct sample rate and a 90 minute presentation is in perfect sync all the way through!

    Cheers, Iain

  2. Andrea says:

    I have just started working with Final Cut Pro 6. I have about a 30 minute video and towards the end the video and audio don’t match up. The video is behind the audio. Is there any way to fix this without starting all over again?

    Thanks so much,

    Andrea

  3. Daniel says:

    I’m experiencing an issue when exporting from FCPX both as Master, and for Youtube, where the audio drifts out of sync in the exported version, yet it seems fine within FCPX. I’m using FCPX 10.0.9. I’m suspecting that it may have to do with some 48K audio wav files that I used in the project. I assumed that Wav and Aiff were close enough there wouldn’t be a problem. Have you ever heard of or experienced a problem like this?

  4. Robert says:

    Hi Larry,

    I’ve been having an audio sync drift issue that no matter what I do I, can’t seem to figure out a solution for.

    I recently recorded sound for a film on a Tascam DR-680 and the footage was shot on the Black Magic Cine Camera. The sample rate was 48 kHz for both the camera and the mixer and the film was shot in 24 FPS. The bit rate was 24 for the Tascam but 16 for the camera (which you can’t change) but I’ve read having a different bit rate shouldn’t effect things. I’m editing on FCP 7 and all the sound files are WAV.

    When I sync up the clips, they start in sync and gradually drift out of sync by about 7 – 10 frames by the end of a clip that’s around 4 minutes long. The footage is pro res LT but I’ve never had a problem with that codec with any other camera. I tried converting the WAV files to AIFF but there was no change. I also tried the deleting preferences route but there was no change there as well. I don’t think its the mixer because I’ve done shoots with that and a Sony FS 100 and its synced up perfectly and I don’t think my macbook pro retina could have anything to do with it either; it only has happened with the Black Magic camera. I’ve had no luck finding answers while scouring the Internet and am at my wits end. Do you have any suggestions? If you would need any additional information to help me figure out the answer let me know but I think I covered most of the bases.

    Thanks!

    Robert

    • Larry Jordan says:

      Robert:

      I *think* this is a frame rate issue, which, normally, wouldn’t affect audio.

      But the very slow sync drift is acting like one file is recorded at 24 fps, while the other is recorded at 23.976.

      That would account for the difference. I would contact Tascam and see if they have a solution.

      Larry

  5. arnaud says:

    Hi all,
    Just to let you know I’he had the same problem with 5Dmkii video shot 25fps ( hello France )
    The sound was drifting gradually.
    I’ve set the sound to 48hz same as video, and change the speed to 100,3 %
    I still don’t understand why but it works, seems to be a pb with the prores 422 format.
    Hope this will help.
    Thanks

  6. David Bernstein says:

    Hi y’all,

    I’ve been searching and reading so many blogs about this. It seems to be an ongoing error and no one I found yet had a good answer.

    Thank you Arnaud for your simple but amazing suggestion to change the speed. This worked for me as a temporary solution. I changed the sound file to 48khz and then changed the speed of my audio file to 99.90% and now it’s in sync with the audio of the camera’s built in mic. Amazing.

    I have read on another blog: http://forums.creativecow.net/thread/8/1120919

    that they suggested to make the edit of the video in final cut pro and then bring the exported video file into Protools to then sync with the audio there and apparently that works too. Though I don’t have protools so this is what I got for now.

    Good luck and I hope the next person who reads this doesn’t have to suffer like all the rest of us wasting so much time on this.

  7. Kristof Deak says:

    Hey guys, it seems I have stumbled upon a solution to this issue.
    It’s a software bug in FCP7 so don’t look for an explanation, it’s just how it is for no reason.
    So in my own experience, even exporting a .wav and then re-importing the same (!) file resulted in this sync-drift issue.
    The trick is that the time code of all files imported gets automatically aligned with the FPS setting of FCP.
    Now, counter-intuitively, FCP takes the fps data NOT from the sequence settings, not from the files themselves – but from the Easy Setup template setting!
    So for example, if your sound file is coming from a 23.98fps project, but your Easy Setup is accidentally set to 25fps, it will always drift out of sync (or just simply won’t relink without problems)

    The solution: set your FPS to the correct rate in Easy Setup BEFORE importing the file that’s the culprit and then quit and RESTART FCP.
    To re-iterate: you can’t have any files in your project already imported at the wrong frame rate (because the new imports will just assume the same rate) – you need to start fresh, change the setting, restart FCP (the change won’t take effect without restarting) and THEN import the same files.

    This solution has worked for me every time. The only other option is retiming/time stretching the audio to fit (press ‘sss’ and drag) but that affects quality.

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  9. lily says:

    Hello I have a problem with audio sync drift in final cut pro 7
    I shot in AVCHD and recorded the audio in MP3.

    For editing I converted the AVCHD files to MP4s and then to apple pro res 422
    I have converted the MP3s into Aif files.

    I have set the sequence settings before importing the files to 48hrz and 16bit (which is the audio setting for both my video files and separate audio files) but still about half way through the timeline the audio slips around 1 second out of sync

    so by process of elimination I know that it is not due to
    – audio sample rates that don’t properly match the audio settings in the sequence
    – trying to edit MP3 files
    – deleting final cut user preferences
    – exporting the file using quicktime in imovie
    None of these things worked for me,
    do you have any suggestions?
    Thank you very much, lily

    • LarryJ says:

      Lily:

      Well… if the audio is DRIFTING out of sync, its caused by a sample rate mis-match. If the audio starts and stays out of sync, or, at some point in the project, JUMPS out of sync, that will be caused by missing audio or missing video.

      First, I would not convert my AVCHD material to MPEG-4, then, again, to ProRes. I would go straight to ProRes from AVCHD.

      Second, what software did you use to convert the MP3 to AIF? My suspicion is that this is the conversion that did not work properly. I would try reconverting your audio using different software and see if the problem goes away.

      Larry

  10. Inshra says:

    Hi Larry,

    It seems I too am having this sync drifting issue and could really use some help.

    I’m trying to export my short film, which I shot on a Canon c300. It’s the final edited and colour graded version, with no sound, just a .mov file. When I put the audio file into the FCP timeline, for final output, I’m getting the sync drift. There’s an ‘x’ in the video file to sync with a beep in the audio file, but after a few minutes the sync is drifting and by the end of the 12 min fill it’s totally out of sync. This is what I did-

    1) I’ve got my final colour graded .mov file, which I made a copy of on Apple Pro Res 422, set it on 48khz.

    2) Then I’ve got my final sound which is a single 48khz .aif file.

    3) I opened a new FCP project, with a sequence setting of 48khz, but the audio sync drift is STILL happening.

    I’m working on FCP 7.0.3 and the final audio file is from Logic Pro 9. How to fix this issue?? Somebody please enlighten me!

    Inshra

    • LarryJ says:

      Inshra:

      Hmmm… If audio sync is drifting, then my first suspicion is that one of these sample rates is not set correctly.

      1. Trash your FCP 7 preferences
      2. Double-check that your project file is 48 kHZ
      3. Add a tone to your entire project, then make it inaudible
      4. Triple check that your audio file is actually 48 kHZ, then add it to your project.

      If things still drift, change the project settings to 44 kHz and see if sync holds.

      Larry

      • Inshra says:

        Trash the FCP preferences? How do I do that? And how do I add a tone to the project? (Advance apologies for silly questions, I’m not a pro)

        The project file is definitely 48khz and I’ve triple checked the audio is 48khz, things are still drifting, I also changed the project settings to 44khz but it’s still drifting. I’m not sure what the problem is at this point.

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