Solving Problems Caused by Audio Sample Rates that Don’t Match

Posted on by Larry

[ This article was first published in the June, 2010, issue of
Larry’s Monthly Final Cut Studio Newsletter. Click here to subscribe. ]


I got burned by this when I was prepping my most recent webinar for posting. My audio slowly slipped out of sync.

I hate when that happens.

What I discovered is that the Soundtrack Pro sample rate preference setting overrides the sample rate of the Final Cut Pro project, resulting in a slow sync drift that will drive you nuts.

Because there are a variety of places where you can choose the wrong sample rate, I wanted to walk you through my process of posting a webinar to show you where the problem occurred and how to prevent it.

I record all my tutorials and webinars using Telestream’s Screenflow. When I am ready to export the file for editing, I always select “Lossless” to give me the highest quality for editing and compression.

Then, for audio, I export the file as a Linear PCM file. (See the article on choosing the right version of “Endian-ism.”)

Here’s the first opportunity you have to screw things up. Notice that the sample rate is set to 48.000 kHz. The problem is that my audio gear, like most audio gear, records at 44.1 kHz. (Both are excellent choices from a quality point of view.)

While Final Cut can easily handle both 44.1 and 48 kHz sample rates, it prefers 48 kHZ. At least, that’s been my experience when working with the Animation codec and synced audio.

So I make sure to set the audio rate to 48 kHz and export.

When getting ready to edit this in Final Cut, I create a new sequence, then drop my clip into it.

If I get a message asking if I want to change the sequence settings to match the clip, I say Yes.

Then, I remove the clip from the sequence and check Sequence > Settings. Removing the clip allows me to adjust all the settings, which can’t be done once a clip is in the Timeline. The main thing I am checking is to be sure my audio sample rate is set to 48 kHz. If not, I change it.

Once I verify my sequence settings are correct, I edit my project as normal. Because both audio and video settings of the clip match the timeline, there’s no rendering until I add effects.

Finally, I do all my audio clean-up and mixing in Soundtrack Pro. Here’s the third place the sample rate can get accidentally reset.

Before sending my file to Soundtrack Pro I SHOULD have (but didn’t) check to be sure the sample rate preference was set correctly.

To check it, go to Soundtrack Pro > Preferences > Project tab and make sure the project sample rate is set to 48000 (48 kHz).

Then, File > Quit Soundtrack Pro.

In Final Cut, select your sequence in the Browser and File > Send it to Soundtrack Pro.

When Soundtrack opens with your sequence in it, be sure the project sample rate is set to 48 kHz. You check it by looking in the top of the Soundtrack Pro tool bar. If this, too, is set to 48 kHz, all your audio sample rates match across all your programs.

At this point, you’ve maintained a consistent sample rate across all your software and elements and sync will remain constant and locked.

Yes, I’ve added this to my editing checklist.

 


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11 Responses to Solving Problems Caused by Audio Sample Rates that Don’t Match

  1. hello, I am having snyc drifting in my 13 minute film when I export the audio only. I bring it back in and it drifts. I have 44 and 48 Khz in the timeline. Is there a way to convert the timeline to have the same sync. Thank you for your time.

  2. Henry B. Lee says:

    You are brilliant! This worked beautifully in repairing my drifting synch issue. Thanks!
    Henry
    New York, NY

  3. Mil-Mil says:

    Larry, I’ve recorded several interviews on a Panasonic PV-GS500 camcorder with 12-bit audio. They are drifting out of sync on FCP X when I transfer them. Does the Sampling rate need to be at 32 kHz? Thanks and any suggestions would be appreciated.

  4. Spud says:

    “Then, I remove the clip from the sequence and check Sequence > Settings. Removing the clip allows me to adjust all the settings, which can’t be done once a clip is in the Timeline. The main thing I am checking is to be sure my audio sample rate is set to 48 kHz. If not, I change it.”

    You are wrong here, FCP 7 does allow you to change sequence settings even with a clip in the timeline.

    • Spud:

      You are correct, mostly. FCP 7 does allow you to change some settings, but not all of them. The biggest example of a non-changeable setting is frame rate. You can only change frame rate when the sequence is empty.

      There are one or two others that I seem to remember can’t be changed, so I long ago made it a habit to only make changes to an empty Timeline.

      Larry

  5. Thom says:

    I have a film whose audio doesn’t match the sample rate of the picture. Any idea how to fix this? I am using FCPX and Logic Pro

    • Larry says:

      Thom:

      Video doesn’t use a sample rate, so there is nothing to match. FCP X can handle audio sample rates of 44,100 and 48,000 bits per second. What problem are you seeing?

      Larry

  6. Nick Crider says:

    Question: I recently recorded using a Midas M32 console. Unfortunately I had the consoles sample rate at 48k but my daw was set to 44.1.
    Now in playback the audio naturally is slowed down and lower pitched. Is there a simple formula I can use to get the audio files to sound natural? (i.e. tune up 2 and speed up 1.10 for example) or a way to convert the audio to sound normal?

    • Larry says:

      Nick:

      I don’t know about ProTools, but I know Adobe Audition has the ability to change the speed of a clip. The conversion amount is 1.08844. At the same time, you need to change the sample rate to 48K.

      Changing the speed, alone, won’t change the sample rate.

      Larry

  7. Ray Mitch says:

    I record audio from 4 dynamic mics into Cubase DAW. at 48k and extract that at 48k rate. I then import it into iMovie to sync with iPhone video at 4k 30fps. I still get audio drift. any help or pointers. Am I doing anything wrong or is it not possible to sync with this setup?

    • Larry says:

      Ray:

      The two 48K files should line up. I wonder if the iMovie frame rate is messing things up. How much is the drift?

      Contact me directly at larry [ at ] larryjordan [ dot ] com.

      Larry

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