Compressor 4 - Limitations of the LFE Channel

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Limitations of the LFE Channel

The Low Frequency Effects (LFE) channel is a separate signal with a limited frequency
range and is created by the mixing engineer and delivered alongside the main channels
in the mix. A “brick wall” filter at 120 Hz in the Dolby Digital Professional encoder limits
use of the LFE channel to the bottom two audible octaves. Dolby recommends limiting
the signal to 80 Hz when mixing your sound.


Chapter 12

Creating Dolby Digital Professional Output Files

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In most music productions (with such exceptions as the famous cannon shots in
Tchaikovsky’s “1812 Overture”), the LFE channel is not necessary. The LFE signal is also
discarded in the Dolby Digital Professional downmix process, so intense bass signals do
not stress small stereo systems. Be sure not to include vital information in the LFE channel
that would be missed in mono, stereo, or Pro Logic 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.

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.