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.

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:

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.

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75 Responses to Solving Audio Sync Drift

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  1. Al says:

    Hi Larry,
    I’m working with FCP7 and have encountered the first audio drift that I have not been able to correct.
    You’re the best. I follow many of your comments and suggestions in your different forums. Figured since you’re the guru of FCP, you’re the man to ask!

    This was my first time filming with an iPhone 14 (presumably at 30 fps). I have an external mike which is set at 48 hz. After a few mins into the recording, on the FCP7 timeline, the audio drifts.
    Plural Eyes synced it all up fine, but when playing on FCP7 it starts drifting.

    Any cure for this? Any suggesting to avoid this happening for future recordings?
    Please share your wisdom, as I tried your idea of re-sampling the audio using compressor from 48 to 44.1 hz and that didn’t seem to help the situation.
    Thanks for any help you can offer.

    • Larry Jordan says:


      My GUESS is that the frame rate for FCP 7 is set incorrectly. Seeing as the audio starts in sync, then drifts out, that tends to suggest that the timeline is set to 29.97, rather than 30. Or, it is set to 30 when it needs to be 29.97.

      Try switching frame rates in the project – remember, you can ONLY do this when the project is empty – and see if that fixes the problem. (You can copy/paste clips to move them from the old project to the news.)


      • al says:

        Hi Larry, thanks for your reply.
        I tried those ideas already, switching the timelines to either 29.97 or 30 fps. Neither helped!
        I used Compressor to change the audio sample rate from its original setting of 48kh to 44.1kh and put those audio clips on both timelines. Still, it won’t match up more than for just a few mins before it starts drifting out again.
        There must be another solution we’re missing here!

        • al says:

          Good day. Was hoping I could still get a reply as to the audio drift issue on FCP7 as outlined above.
          I had tried your suggestion of changeing the timelines, and both at 29.97fps and 30fps, the timelines yielded no success and the drift continued.
          Are there any other possible ways to help avoid a repeat of this in the future with the iPhone and an external recorder? Is there any other option to help correct my current out-of-sync clip?
          Thank you for any help you can offer!

          • Larry Jordan says:


            Depending upon your settings, the iPhone tends to record at 29.97 fps. Ideally, you should have FCP 7 automatically set the frame rate to match the video.

            Then, record audio at 48K sample rate. As always, do a test before a major production. However, while FCP 7 is older software, if frame rates match between video and project, and the SOURCE audio is recorded at 48K, I have not heard of consistent problems.

            Also, be sure to trash FCP preferences before started a new project.


          • al says:

            Thank you. I will make a “test-run” and update you with the results. Appreciate your help!

  2. al says:

    Hi Larry,
    Your suggestion was right on target and worked perfectly!
    iPhone video rate was 29.97fps as well as the timeline
    For some I did have better success with adjusting the audio bit rate down to 44.1k for some reason, especially when a clip ran very long. All in all, the problem has been solved.
    Thank you!

  3. Larry Jordan says:


    Happy to help.


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