Using surround effect plug-ins, Limitations of the lfe channel – Apple Soundtrack Pro 2 User Manual
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Chapter 9
Mixing Surround Sound
311
Using Surround Effect Plug-ins
Soundtrack Pro includes a collection of professional surround-specific effect plug-ins
for shaping your surround mix, including Surround Compressor, Delay Designer, Space
Designer, and Multichannel Gain.
For a complete list of these true surround effects and a full description of each, see the
Soundtrack Pro Effects Reference document, available in the Help menu. For information
about using processing and realtime effect plug-ins, see Chapter 11, “
Limitations of the LFE Channel
Use the LFE (Low Frequency Effects) channel to enhance the low frequencies of a film or
video so you get the extra boom out of an explosion, thump in a car crash, and so on in
dramatic scenes involving plenty of low frequencies. The low frequency effects (LFE)
channel is a separate signal with a limited frequency range (about 25 Hz to 120 Hz). It is
created by the mixing engineer and delivered alongside the main channels in the mix.
In soundtracks comprised entirely of music, the LFE channel is not necessary. (An
exception to this rule might be the famous cannon shots in Tchaikovsky’s “1812
Overture.”) The LFE signal is also discarded in the downmix process, so that intense bass
signals do not stress small stereo systems. Be sure not to include vital information (such
as dialogue) in the LFE channel that would be missed in mono or stereo playback.
Because LFE is separate from other channels, its ability to blend with higher
frequencies can be affected by filters used to generate the LFE signal. To ensure a
cohesive audio signal, keep the entire signal together in the main channel or channels.
Note: If you are creating Dolby Digital Professional (AC3) output, avoid creating an LFE
channel for material originally produced without one. Dolby Digital Professional’s five
main channels are all full-range, and the LFE channel does not increase the frequency
response. Dolby Digital Professional decoders offer bass management, directing low
frequencies to a subwoofer or other suitable speakers. An LFE track may interfere with
bass management. For more information about Dolby Digital Professional, see
“Frequently Asked Questions about Dolby Digital Professional,” available at the Dolby
Laboratories Inc. website: