Apple Final Cut Pro 6 - Manual (Page 324)

Chapter 20 Importing Media Files into Your Project 323
IV
Choosing Audio File Sample Rate and Bit Depth
Final Cut Pro can import audio with any bit depth and sample rate supported by
QuickTime and Mac OS X Core Audio. Final Cut Pro 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.
For more information, see Volume III, Chapter 1, “Audio Fundamentals.”
Choosing Sequence Bit Depth
The bit depth setting in the Sequence Settings window determines the bit depth
whenever you output or export your sequence. However, sequence audio is always
mixed using 32-bit floating-point values.
Note: The Aud Format column in the Browser and Item Properties window always
shows the internal mixing bit depth of a sequence, whereas the Sequence Settings
window shows the bit depth used if the sequence is exported or output via an
audio interface.
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 Pro, 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 Volume III, Chapter 29, “Rendering and
Video Processing Settings.”
Even though Final Cut Pro 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 Pro can mix together in real time.