Changing Audio Capture Settings to 32 kHz

[ This article was first published in the October, 2008, issue of
Larry’s Final Cut Pro Newsletter. Click here to subscribe. ]

Note: In looking over my email for the last couple of months, I’ve been getting a lot of questions about drifting audio sync. if you are capturing a clip and the audio slowly drifts out of sync, you need to pay close attention to this article. This is the classic symptom of shooting audio at one sample rate and capturing at another.

While most professional cameras record audio at a 48 kHz audio sample rate (also called 16-bit in some camera menus), less expensive cameras tend to record audio at a 32 kHz sample rate (which is sometimes called 12-bit audio, just to keep us all confused).

While 32k sample rates are perfectly adequate for recording human speech, it tends to be insufficient to adequately record music. More importantly, Final Cut defaults to capturing all audio at 48 kHz. When the audio isn’t captured at the same rate at which it was shot, the audio slowly drifts out of sync.

To fix this, you need to change your audio capture settings before you capture any clips. Here’s how.

1. First, determine what sample rate your camera records audio. This is generally done by checking the audio setting in your camera menu. If it says 48 kHz or 16-bit, you don’t need to do anything. Feel free to jump to the next article.
2. If it is set to 32 kHz, or 12-bit, you need to do two things: change the camera settings so it records all future audio at 48 kHz, then, create a new setting in Final Cut so that it will properly capture any material that you’ve already shot.

   It is generally considered best practice to shoot all your audio at the same settings and 48 kHz is considered a professional audio sample rate.

3. To create a new capture setting, open Final Cut Pro and go to Final Cut Pro > Audio / Video Settings.



4. Click the Capture Presets tab.



5. Select the video format that matches what you are shooting in your camera. In this case, I’m using DV NTSC 48 kHz.The lock at the right side indicates this is an Apple preset that can not be deleted or modified. Click the Duplicate button at the bottom to make a copy of this preset.



6. In the Capture Preset Editor dialog box, give the new capture preset a name, for instance “DV NTSC 32 kHz,” then look to the lower right and change the audio Format menu from 48 kHz to 32 kHz.
7. Click OK to create the new preset. Put a check mark next to it in the Capture Presets tab, then click OK again.

You are now ready to capture your 32 kHz audio.

Remember to go back to the Audio / Video settings menu and change your capture preset when you need to capture audio at 48 kHz.

UPDATE – Oct. 11

Sabrina Nelson adds:

Capturing 32khz 12bit audio is the bane of my existence… until now, I’d refused to work on any project that was recorded in that way. I’ve spent days redubbing tapes to DVNTSC48k for one naughty client, and suddenly I see your timely tip and is like, “Wow, I coulda had a V8!”. Thank you for the tip on creating a new preset. Its so simple, I should have thought of it 😛

Larry replies: Thanks.

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