Choosing audio file sample rate and bit depth – Apple Final Cut Express 4 User Manual
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Part IV
Choosing Audio File Sample Rate and Bit Depth
Final Cut Express can import audio with any bit depth and sample rate supported by
QuickTime and Mac OS X Core Audio. Final Cut Express performs real-time bit depth
conversion and sample rate conversion when your audio file settings don’t match your
sequence settings. However, less processor power is required when your audio file
settings and sequence settings match.
Common sample rates and bit depths used in the video industry are:
 32 kHz/12-bit: Consumer mini-DV camcorders can record four channels of audio
using these settings. This is not recommended for most productions.
 44.1 kHz/16-bit: Audio CDs and consumer DAT recorders use these audio settings.
 48 kHz/16-bit: DV, HDV, and DVD all use these audio settings.
 48 kHz/20-bit: Some professional video devices record natively in this format.
 96 kHz/24-bit: These settings are becoming increasingly popular for professional
sound and music production, although most video formats still record with 48 kHz.
Mixing Sample Rates and Using Real-Time Sample Rate Conversion
Ideally, the sample rate and bit depth of your audio files should match that of your
sequence settings. When you play a sequence in Final Cut Express, any audio files with
sample rates that don’t match your sequence sample rate are converted in real time.
This is known as sample rate conversion, and it requires additional processing power.
Clip items that require real-time sample rate conversion appear with a green render bar
within the clip item. For more information, see Chapter 57, “
Even though Final Cut Express can perform real-time sample rate conversion,
conversions can reduce your audio mixing and effects performance. The quality of this
conversion is controlled by the Audio Playback Quality setting in the General tab of the
User Preferences window. Higher-quality conversions reduce the number of audio
tracks that Final Cut Express can mix together in real time.
If the sample rates of all the audio matches that of the sequence match, sample rate
conversion is not necessary and the number of audio tracks that can play in real time
increases. If you are working with someone who is creating music or audio files
specifically for your project, you can request audio files at the settings you need to
match your sequence.
However, if your audio clips don’t match your sequence settings, you can improve
audio playback performance by converting your audio files to the sample rate and bit
depth of your sequence.