Apple Final Cut Pro 5 - Manual (Page 315)

314 Part IV Logging, Capturing, and Importing
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 24, “Rendering.”
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 postproduction, they are used for most sequences in Final Cut Pro.
Important: DV sequences sometimes use 32 kHz/12-bit settings, but these settings are
not recommended. As long as you don’t record your DV footage using 32 kHz/12-bit,
you should not use these settings for your sequence.
Audio files can be converted using the Export Using QuickTime Conversion command.