Apple Logic Pro 8 - Manual (Page 853)

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Working With Split Channel Audio
File Formats
You can store multi-channel audio as interleaved or split
channel audio files.
An interleaved audio file contains all channel information, stored in an alternating
single “stream.”
 For stereo files, this would be left channel, right channel, left, right, and so on.
 For surround files, this would be channel 1, channel 2, channel 3, and so on, then
back to channel 1. Put into the context of a 5.1 surround mix: left, center, right, left
surround, right surround, LFE (then back to left, center, and so on) in a six channel
interleaved file.
Split channel audio files couple separate audio files, allowing you to deal with each
channel (file) independently.
 For stereo files, two separate files are created, where one file contains the left
channel samples, and the other file contains the right channel samples. The files are
generally identified by a .L and .R suffix. The two files are linked, and are edited as a
pair. You can, however, disconnect them (in the Audio Bin), allowing each to be
handled independently.
 For multi mono (or split surround) files, multiple mono files are created: one for each
surround channel. As with split stereo, each file is identified by a suffix. This is
commonly as follows for a 5.1 surround mix: .L, .C, .R, .Ls, .Rs, and .LFE. Each file is
independent.
Logic Pro, and most other audio applications, support the import and recording of
interleaved files when using Core Audio hardware.
A handful of audio applications (including Pro Tools) only support split file formats, and
will automatically separate interleaved files when you import them. This is also true of
Logic Pro when importing interleaved stereo files using DAE/TDM hardware (Logic Pro
does not support split surround files).
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Tip: You should use interleaved audio files if your audio hardware supports them. Split
channel audio files require significantly more hard disk I/O performance.