Apple Logic Express 7 - Manual (Page 207)

Chapter 6 Logic’s Mixing Facilities 207
MP3 Options in the Bounce Dialog Window
Logic allows the bouncing of MP3 (MPEG-2-Layer-3) format files. This well-known data
reduction format for digital audio signals was developed by the Fraunhofer Institute,
and allows high compression rates while maintaining quite good audio quality
(depending on the compression rate). MP3 is the current standard for audio file
exchange via the Internet.
Due to the fact that encoding an MP3 file equates to a loss of audio quality, you should
not use MP3 files during production if you have access to the same audio data in linear
formats such as: AIFF, WAV, or SDII.
Bounced PCM file(s) is/are also used for encoding to MP3/AAC or burning a CD. It
should be noted that this occurs before dithering takes place.
Note: Should the selected sample rate be higher than 48 kHz, a temporary copy of the
bounced PCM file is created—with an automatic sample rate conversion to 48 kHz
before encoding. This conversion takes place because the MP3 format does not support
sampling rates higher than 48 kHz.
If the PCM option is disabled in the Destination menu, a temporary PCM file is bounced
as a source for encoding to MP3/AAC and/or burning to a CD—in accordance with the
options selected in the PCM page.
Bit Rate (Mono/Stereo)
MP3 bit rates are selectable between 8 kbps and 320 kbps, but default to 80 kbps
mono, and 160 kbps stereo. These rates offer acceptable quality and good file
compression. If you can afford the extra file size, we recommend selecting 96 kbps for
mono and 192 kbps for stereo streams, as this provides better audio quality. You can, of
course, choose even higher rates, but the quality improvement afforded by bit rates
above 96/192 kbps is nominal.
Use Variable Bit Rate Encoding (VBR)
Variable Bit Rate encoding compresses simpler passages more heavily than passages
that are (more) harmonically rich, generally resulting in better quality MP3s.
Unfortunately, not all MP3 players can accurately decode VBR-encoded MP3s, which is
why this option is turned off by default. If you know that your target listener/s can
decode VBR-encoded MP3s, you can switch this option on.
Quality
Keep this set to Highest whenever possible. Reducing the quality accelerates the
conversion process, but at the expense of audio quality.
Use Best Encoding
Again, like the Quality parameter, if you uncheck this option, you will gain encoding
speed at the price of audio quality. This should always be kept on, unless conversion
time is an issue.