Low-frequency effects
The low-frequency effects (LFE) channel is a band-limited audio track that is used for reproducing deep and intense low-frequency sounds in the 3–120 Hz frequency range.[1] [2] [3] [4]
This track is normally sent to a
Types
Low-pitched musical arts
LFEs include both low-pitched musical notes and low-pitched sound effects. The musical
Sound effects
The most challenging sounds to reproduce from a sound engineering standpoint are usually the extremely low-pitched
It is a formidable challenge for an amplifier, subwoofer speakers, and cabinet to reproduce these sound effects at a high volume without encountering 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 World War II film U-571 (2000) to test the accuracy of subwoofer systems.[5]
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 a straightforward installation of extra dedicated subwoofers, and removed the need to upgrade the main speakers.
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 a bass management system to redirect bass from all channels to a subwoofer.
Home theater systems
In the 1990s
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 surround sound programming, while the subwoofer output is bass information from up to all six channels that has been selected to be reproduced by the subwoofer via a 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 channel.
Bass Shaker
The LFE channel can be output to one or more tactile transducers, also known as "bass shakers". When connected to the subwoofer output, the bass shaker will vibrate at the frequency of the bass, usually between 20 and 200 Hz, without producing much audible sound. Tactile transducers are frequently mounted directly to the frame of a chair or sofa. A listener's body can feel the vibrations from the LFE, enhancing the overall sensation of the bass.
See also
References
- ^ a b "What is the LFE channel?" (PDF). Dolby Laboratories, Inc. 2000. Retrieved 2021-04-11.
- ^ "5.1-Channel Production Guidelines" (PDF). Dolby Laboratories, Inc. 2000. Retrieved 2021-04-11.
- ^ "5.1-Channel Music Production Guidelines" (PDF). Dolby Laboratories, Inc. 2005. Retrieved 2021-04-11.
- ^ Mason, Andrew (August 2011). "Use of the low frequency effects (LFE) channel in broadcasting" (PDF). BBC Research and Development White Paper WHP 203. Retrieved 2021-04-11.
- ^ a b Kumin, Daniel (June 2005). "Tiny Killer Subs – Can you get big bad bass from little bitty boxes?". Sound & Vision. Retrieved 2021-04-11.