Apple Soundtrack Pro 3 - Manual (Page 352)

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 (AC-3) 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 the Dolby
Laboratories Inc. website at
http://www.dolby.com .
Accommodating Stereo Playback
Even with the popularity of 5.1 systems, you should always address stereo reproduction.
There are three basic ways to do this:
• Prepare a new stereo mix from the original multitrack elements (using conventional
stereo-mixing sessions).
• Prepare a studio-adjusted downmix from the multichannel mix. This method takes
advantage of the work that has gone into mixing the 5.1 version. It retains flexibility in
the exact proportions of each channel represented in the final stereo mix.
• Let the decoder derive a stereo downmix, based on preset formulas in the decoder.
Downmix options and dynamic range control effects can be previewed and adjusted
in the production studio, and a range of adjustments is possible.
Tip: Always check the mix on an inexpensive surround system to evaluate how well it
sounds on modest playback systems.
352 Chapter 13 Mixing Surround Sound