Apple Compressor 2 - Manual (Page 176)

176 Chapter 12 Creating QuickTime Movie Output Files
Sound Sampling Rates
Digitized sound consists of sound samples captured at different frequency rates. The
more sound samples per second, the higher the sound quality. For example, audio CDs
use a 44.1 kHz sampling rate, DVDs sample at 48 kHz, and telephone networks sample
voices at 8 kHz. The sample rate you choose depends on the nature of the sound. Music
requires a higher sampling rate than voice, because music contains a wider range of
frequencies. Spoken voice has a more limited range of frequencies, so you can choose a
lower sampling rate and still maintain acceptable audio quality. In most cases, you
should choose the highest sampling rate available.
Reducing the sampling rate can shrink a media file by as much as 5:1. The audio quality
will be affected, but not as much as it would be if you used 8-bit sampling. The
following table shows common sampling rates and the audio device quality to expect
at each rate:
Sound Sampling Size
The sound sampling size determines the dynamic range of the sound. 8-bit sound
provides for 256 possible values, whereas 16-bit sound allows for more than 65,000
possible values.
Choose 16 bit for music that has both soft and loud sections, such as orchestral music.
For spoken voice or music that has a more or less constant volume level, choosing 8 bit
can still yield good results.
If you need to shrink your media file, you can reduce the sample size from 16 bit to
8 bit. This cuts the file size in half but also degrades the audio quality.
Sample rate Audio device quality
48 kHz DAT/DV/DVD
44 kHz CD
22 kHz FM radio
8 kHz Telephone