Apple Final Cut Pro 7 - Manual (Page 379)

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.
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
“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.
If the sample rates of all the audio in your 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.
Converting Audio Clips to Match Sequence Settings
If you are working with preexisting audio material, such as music from audio CDs, you
need to convert the audio files so they match your sequence settings. For example, if you
plan to use a lot of sound effects or music from audio CDs (which have a sample rate of
44.1 kHz) in a DV sequence with a sample rate of 48 kHz, it’s a good idea to convert your
audio files to a sample rate of 48 kHz.
Most professional video formats, including DV, have a sample rate of 48 kHz and a bit
depth of 16 (this is often abbreviated as 48 kHz/16-bit). Since these settings are so common
for video post-production, they are used for most sequences in Final Cut Pro.
379 Chapter 26 Importing Media Files into Your Project