Low-Frequency Effects (LFE) is the name of an audio track specifically intended for deep, low-pitched sounds ranging from 10-120 Hz. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. This track is normally sent to a speaker that is specially designed for low-pitched sounds called the subwoofer or Low Frequency Emitter. A subwoofer is a Woofer, or a complete Loudspeaker dedicated to the reproduction of bass audio frequencies, from perhaps 150 Hz down 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. Dolby Stereo (or Dolby Analog) was the original analog optical technology developed by Dolby Laboratories for 35 mm film prints in 1976 Home cinema, also called home theater, are entertainment systems that seek to reproduce cinema quality video and audio in a private home DVD (also known as " Digital Versatile Disc " or " Digital Video Disc " - see Etymology)is

LFE is sometimes expanded as Low Frequency Enhancement^[1].

Types

Low-pitched musical parts

LFEs include both low-pitched musical notes and low-pitched sound effects. The musical soundtrack for many films includes bass instruments that produce very low notes. Until the 1970s, most of the low-pitched instruments were natural, acoustic instruments, such as the double bass or the pipe organ's pedal keyboard. The double bass is the largest and lowest-pitched bowed String instrument used in the modern symphony orchestra. The pipe organ is a Musical instrument that produces sound when pressurized air (wind is driven through a series of pipes, controlled by a keyboard A pedalboard (also called a pedal keyboard pedal clavier or with electronic instruments a bass pedalboard is a keyboard played with the feet that is usually used to After the 1980s, film scores increasingly used synthesized instruments, including synth bass keyboards, which included very low-pitched notes. The bass synthesizer (or "bass synth" is an Electronic instrument capable of producing a variety of sounds by generating and combining signals of different frequencies

Sound effects

The most challenging sounds to reproduce from a sound engineering soundpoint are usually the extremely low-pitched sound effects in the 20 Hz range, such as those used to simulate the sound of an earthquake, a rocket launch, or submarine depth charges. For the album by The Jam see Sound Affects. Sound effects or audio effects are artificially created or enhanced Sounds These sound effects are at the threshold of human hearing, so it takes a tremendous amount of amplification for the human ear to hear them. As well, since they are sound effects, they may have a longer duration or sustain than many low-pitched musical notes, which makes them harder to accurately reproduce.

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). A Bass reflex system (also known as a ported, vented box or reflex port) is a type of Loudspeaker enclosure that uses the sound 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. U-571 is a 2000 film directed by Jonathan Mostow, and starring Matthew McConaughey, Bill Paxton, Harvey Keitel,

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. Dolby Stereo (or Dolby Analog) was the original analog optical technology developed by Dolby Laboratories for 35 mm film prints in 1976 The LFE channel is conventionally played back 10 dB louder than the main channels, giving significantly more recording headroom. The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to In a digital and analog audio systems headroom is the amount by which linear signal capabilities exceed actual signal level Also, the separate recording allowed straightforward installation of extra dedicated subwoofers, removing the need to upgrade the main speakers, or install an extra LFE Crossover. LFE ( Low-frequency effect) Crossover, a basic form of Bass management, is a technical method in audio equipment to cross-feed a low frequency part of the sound spectrum

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). Dolby Digital is the marketing name for a series of lossy audio compression technologies developed by Dolby 70 mm film (or 65 mm film) is a wide high-resolution film gauge of superior quality to standard 35 mm motion picture film format. LFE ( Low-frequency effect) Crossover, a basic form of Bass management, is a technical method in audio equipment to cross-feed a low frequency part of the sound spectrum

Home theater systems

In the 2000s, many western consumers began purchasing "surround sound" home theater systems to enhance the experience of viewing DVD films. 51, Multichannel audio, Multichannel music Surround 3D Surround 5 Home cinema, also called home theater, are entertainment systems that seek to reproduce cinema quality video and audio in a private home Prior to the advent of home theater systems, when VCRs were used, the enhanced sound option was stereo high-fidelity sound. With home theater systems, a multichannel audio system was used to deliver different sounds to six or more different speakers. The widely-used 5. 1-channel audio system consists of five full range main (Left, Center, Right, Left rear Surround, and Right rear Surround) plus a Low-Frequency Effects (LFE) channel.

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. CrossOver (known before version 60 as CrossOver Office) is the collective name for three commercial and proprietary programs developed by CodeWeavers The fundamental principle of bass management in Surround sound replay systems is that bass content in the incoming signal irrespective of channel should be directed only to

In surround sound systems, 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".

See also

• Surround sound
• LFE Crossover

References

External links

• Dolby Laboratories - What is the LFE channel? (PDF)