Low-Frequency Effects (LFE) is the name of an audio track specifically intended for deep, low-pitched sounds ranging from 3-200 Hz. This track is normally sent to a speaker that is specially designed for low-pitched sounds called the subwoofer or Low Frequency Emitter. While LFE channels originated in Dolby Stereo 70 mm film prints, in the 1990s and 2000s they became commonplace in home theater systems used to reproduce film soundtracks for DVDs.
LFE is sometimes expanded as Low Frequency Enhancement.
It is a formidable challenge for an amplifier, subwoofer speakers, and cabinet to reproduce these sound effects at a high volume without problems such as power amplifier clipping (distortion), unwanted rattle or resonance in the wooden cabinet, or excessive "chuffing" sounds from the bass reflex vent (if a vent or port is used in the cabinet). Sound recording magazines sometimes use the loud, rumbling sound effects simulating the sound of the submarine depth charges which were used in the WW II film U-571 (2000) to test the accuracy of subwoofer systems.
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 (LFE Crossover).
The LFE channel delivers bass-only information to supplement the overall bass content. The LFE channel content is not the same as the content of a subwoofer-out jack. The LFE channel is used to carry additional bass information in the Dolby Digital program, while the subwoofer output is bass information from up to all six channels that has been selected to be reproduced by a subwoofer, either by a simple crossover network, which filters out all but the low frequencies, or with a more sophisticated digital bass management system.
The bass management in surround sound replay systems is that bass content in the incoming signal, irrespective of channel, should be directed only to loudspeakers capable of handling it. The bass management system may direct bass to one or more subwoofers (if present) from any channel, not simply the content of the LFE. As such, it is incorrect to call the LFE the "subwoofer channel".
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