[ This article was first published in the March, 2009, issue of
Larry’s Final Cut Pro Newsletter. Click here to subscribe.
Updated: 5/31/10 ]
One of the questions I get asked frequently is how to solve a problem where audio is slowly drifting out of sync, or an error message appears saying that the capture or sequence settings don’t match the audio rate.
In all these cases, the problem is the audio sample rate used by your camera.
While virtually all professional cameras record audio at a 48 kHz sample rate (sometimes called 16-bit, though this number has nothing to do with audio bit-depth), most consumer cameras are preset to record audio at 32 kHz. There are some marketing benefits to this setting, but no technical or audio benefits to recording at 32 kHz.
NOTE: The sample rate determines the frequency response of the audio our cameras record. In general, the higher the sample rate, the higher the fidelity – or accuracy – of the sounds being recorded. A 48 kHz sample rate has a frequency rate that exceeds the range of human hearing, while a 32 kHz sample rate is not quite as high a quality.
While bar fights have broken out over how much we should worry about this, my general feeling is that recording your audio at 48 kHz generates professional results and is the sample rate FCP is optimized for. If possible, set your camera to record all audio at 48 kHz. Then, read the rest of this article on how to capture the material that you’ve already shot.
Unfortunately, once audio has been recorded, you can’t change the sample rate on the tape. Instead, we need to change the way Final Cut processes the audio.
Just as you need to tell Final Cut what video format you are using, you also need to tell Final Cut the audio settings. Fortunately, the audio settings are few and easy to change — if you know where to look.
And that is what this technique is about.
First, take a look at the menus on your camera. If the audio is set to record at 32 kHz or 12-bit, then, you’ll need to make these adjustments. Or, if you have a friend with this problem, share this article with them.
If your camera says it is recording audio at 48 kHz, or 16-bit, don’t touch a thing. Your camera and Final Cut are perfectly suited to one another.
But, if these don’t match there are two settings that need to be adjusted in Final Cut so that it will process your audio properly:
CHANGING THE CAPTURE SETTING
NOTE: Before you can change the capture setting, you’ll need to connect your camera or deck to your computer. Be sure to turn on your camera before starting Final Cut Pro.
To change the capture setting, go to: Final Cut Pro > Audio / Video Settings.
There are five tabs across the top. We will be working in tab number 2 and 3.
Click the Capture Preset tab to select it.
In the list below it are all the different video formats that FCP supports. Notice how almost all of them list the audio as 48 kHz?
NOTE: The little lock icon, on the right side, indicates this is one of the essential presets shipped by Apple. The lock means you can’t delete it. While this is not, completely, true, in general, you don’t mess with these locked settings. Instead, we will duplicate the setting and modify the duplicate.
Click the Duplicate button.
In the setting screen that appears, change the title so that it reflects this is a 32 kHZ setting. While this is just a label, make it clear enough so that you will know to select this again if you need it in the future.
The real work is below, in the QuickTime Audio section. Change this from its default setting of 48 kHz, to 32 kHz. Then, click OK.
That’s it. You’ve told FCP to capture all audio at 32 kHz.
NOTE: Here’s the trap. As long as you capture your audio properly, FCP can handle 32, 44.1, and 48 kHz audio on the same Timeline with no problem. But if it is NOT captured properly, FCP can’t fix it afterward. That’s why this setting is so important.
Now, whenever you need to capture 32 kHz material, just select the setting you just created. (The check-mark to the left of the title indicates that this is the currently active capture setting.)
You could stop here. But, if you want FCP to play 32 kHz audio on the timeline without rendering it, you’ll need to change the Sequence setting as well.
NOTE: Remember! Changing a preference setting has NO affect on any existing sequences or clips. You must change the preference setting BEFORE capturing any clips, or creating a new sequence. Once a sequence has been created, changing preferences does nothing.
Click the Sequence Preset tab to select it.
Duplicate the video format that you want to set to 32 kHz.
Change the name of the preset so you can easily find it again.
Then, in the lower right corner of the window, change the audio setting from 48 kHz to 32 kHz. Click OK to save your work.
Now, when you want to capture 32 kHz material, change to the Capture setting you just created.
When you want to edit 32 kHz material to your timeline without FCP needing to render it, change to the Sequence setting you just created.
If you need to adjust an existing sequence so that it will play 32 kHz audio without rendering, open the sequence you want to change into the Timeline.
Be sure the Timeline is selected and choose Sequence > Settings.
In the lower right corner, change the audio setting from 48 kHz – the default – to 32 kHz. At which point, all 48 kHz audio will probably need to render, but all your 32 kHz material will play perfectly without rendering.
NOTE: Changing the audio setting of the sequence is simply an issue about rendering. FCP will properly handle 32, 44, and 48 kHz – however, depending upon your sequence settings, it may need to render audio files that don’t match the sequence setting.