LFE
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LFE, an abbreviation for Low-Frequency Effects, is commonly used in describing an audio track contained within a motion picture sound mix. The signal from this track, ranging from 10 Hz to 120 Hz, is normally sent to a subwoofer, known as the Low Frequency Emitter.
[edit] Development
The LFE channel originated in Dolby Stereo 70 mm Six Track film prints, as a way of providing louder bass and sub-bass effects, without detracting from the quality of the standard audio channels. The LFE channel is conventionally played back 10 dB louder than the main channels, giving significantly more recording headroom. Also, the separate recording allowed straightforward installation of extra dedicated subwoofers, removing the need to upgrade the main speakers, or install extra crossovers.
Later formats such as Dolby Digital retained the LFE channel, although this is more through convention and backwards compatibility than necessity, as digital formats have greater dynamic range than the magnetic analogue recordings on 70 mm prints, and modern sound processors have bass management functions to redirect bass from any channel to a subwoofer.
