Echo chamber

Last updated March 28, 2024

An echo chamber is a hollow enclosure used to produce reverberation, usually for recording purposes. A traditional echo chamber is covered in highly acoustically reflective surfaces. By using directional microphones pointed away from the speakers, echo capture is maximized. Some portions of the room can be moved to vary the room's decay time. Nowadays, effects units are more widely used to create such effects,^[1] but echo chambers are still used today, such as the famous echo chambers at Capitol Studios.^[2]

In music, the use of acoustic echo and reverberation effects has taken many forms and dates back many hundreds of years. Sacred music of the Medieval and Renaissance periods relied heavily on the composers' extensive understanding and use of the complex natural reverberation and echoes inside churches and cathedrals. This early acoustical knowledge informed the design of opera houses and concert halls in the 17th, 18th, and 19th centuries. Architects designed these to create internal reflections that would enhance and project sound from the stage in the days before electrical amplification. Sometimes echo effects are the unintentional side effect of the architectural or engineering design, such as for the Hamilton Mausoleum in Scotland, which has one of the longest reverberation times of any building.^{[ citation needed ]}

Electro-acoustic

Developments in electronics in the early 20th century—specifically the invention of the amplifier and the microphone—led to the creation of the first artificial echo chambers, built for radio and recording studios. Until the 1950s, echo and reverberation were typically created by a combination of electrical and physical methods.^[1]

Acoustically speaking, the "classic novel" echo chamber creates echoes in the same way as they are created in churches or caves—they are all simply large, enclosed, empty spaces with floors and walls made of hard materials (such as polished stone or concrete) that reflect sound waves well. The basic purpose of such chambers is to add colour and depth to the original sound, and to simulate the rich natural reverberation that is a feature of large concert halls.

The development of artificial echo and reverberation chambers was important for sound recording because of the limitations of early recording systems. Except in the case of live performances, most commercially popular recordings are made in specially constructed studios. These rooms were both heavily insulated to exclude external noises and internally somewhat anechoic—that is, they were designed not to produce any internal echoes or sound reverberation.

Because virtually every sound in everyday life is a complex mixture of direct sound from the source and its echoes and reverberations, audiences naturally found the totally 'dry' and reverberation-free sound of early recordings unappealing. Consequently, record producers and engineers quickly came up with an effective method of adding "artificial" echo and reverberation that experts could control with a remarkable degree of accuracy.

Producing echo and reverberation in this form of echo chamber is simple. A signal from the studio mixing desk—such as a voice or instrument—is fed to a large high-fidelity loudspeaker located at one end of the chamber. One or more microphones are placed along the length of the room, and these pick up both the sound from the speaker and its reflections off the walls of the chamber. The farther away from the loudspeaker, the more echo and reverberation the microphone(s) picks up, and the louder the reverberation becomes in relation to the source. The signal from the microphone line is then fed back to the mixing desk, where the echo/reverberation-enhanced sound can be blended with the original 'dry' input.

An example of this physical effect can be heard on the 1978 David Bowie song "Heroes", from the album of the same name. The song, produced by Tony Visconti, was recorded in the large concert hall in the Hansa recording studio in Berlin, and Visconti has since been much praised for the striking sound he achieved on Bowie's vocals. Visconti placed three microphones at intervals along the length of the hall; one very close to Bowie, one halfway down the hall, and the third at the far end of the hall. During the recording, Bowie sang each verse progressively louder than the last, and as he increased volume in each verse, Visconti opened up each of the three microphones in turn, from closest to farthest. Thus, in the first verse, Bowie's voice sounds close, warm, and present; by the end of the song, Visconti has mixed in a large amount of signal from all three microphones, giving Bowie's voice a strikingly reverberant sound.

The original echo chamber at EMI's Abbey Road Studios was improved by Clive Robinson, site foreman at the time of construction. His construction and engineering teams perfected the echo booth at Abbey Road Studios in London. It was one of the first studios in the world to be specially built for recording purposes when it was established in 1931; it remains in place and is a prime example of the early 20th-century electro-acoustic echo chamber.

Buildings such as churches, church halls, and ballrooms have often been chosen as recording sites for classical and other music because of their rich, natural echo and reverberation characteristics. Famous examples include Sir George Martin's AIR Studios at Lyndhurst Hall in Belsize Park, London, a large, vaulted 19th-century building originally constructed as a church and missionary school. Montreal's Church of St. Eustache is the favored recording venue of the Montreal Symphony Orchestra and many others and is much sought after for classical recordings because of its unique acoustic characteristics. The distinctive reverberation on the early hit records by Bill Haley & His Comets was created by recording the band under the domed ceiling of Decca's studio in New York City, located in a former ballroom called The Pythian Temple.

Some recording companies and many small independent labels could not afford large purpose-built echo chambers such as the Abbey Road Chamber, so enterprising producers and engineers often made use of any large reverberant space. Corridors, lift-wells, stairwells, and tiled bathrooms were all used as substitute echo chambers. Many famous soul music and R&B music recordings released by the New York-based Atlantic Records feature echo and reverb effects produced by simply placing a speaker and microphone in the office bathroom—a process also used by Producer/Engineer Bruce Botnick while recording The Doors for their 1970 album L.A. Woman .

Electronic echo machines

The Roland RE-501 is an audio effects device capable of creating echo, chorus, reverb and sound on sound type effects RE-501.jpg — The Roland RE-501 is an audio effects device capable of creating echo, chorus, reverb and sound on sound type effects

In the 1950s and 1960s, the development of magnetic audio tape technology made it possible to duplicate physical echo and reverberation effects entirely electronically. The Watkins Copicat, designed and built by renowned British electronics engineer Charlie Watkins in the late 1950s, is typical of this kind of electronic delay device.

Tape echo units use an endless loop of magnetic tape, which is drawn across a series of recording and playback heads. When a signal from a voice or instrument is fed into the machine, it records the signal onto the tape loop as it passes over the record head. As the tape advances, the newly recorded signal is then picked up by a series of playback heads mounted in line with the record head. These play the sound back as the signal passes over each head in turn, creating the classic rippling or cascading echoes that are typical of tape echo units.

The number of playback heads determines the number of repeats, and the physical distance between each playback head determines the ratio of delay between each repeat of the sound (usually some fraction of a second). The actual length of the delay between each repeat can be varied by a pitch control that alters the speed of the tape loop across the heads.

Typically, the playback heads of tape echo machines are also connected to controls that allow the user to determine the volume of each echo relative to the original signal. Another control (sometimes called "regeneration") allows the signal from the playback heads to be fed back into and variably mixed with the original input signal, creating a distinctive "feedback" effect that adds more and more noise to the loop with each repeat. If fully activated, this control ultimately produces a continuous feedback loop of pure noise. Roland manufactured various models of magnetic tape echo and reverb sound effect machines from 1973 until the introduction of digital sound effect machines.

A tape echo that has few repeats and a very short delay between each repeat is often referred to as a "slapback" echo. This distinctive sound is one of the key sonic characteristics of 1950s rock and roll and rockabilly, and can be heard on the classic mid-50s Sun Records recordings by Elvis Presley and others. This effect was a result of the unintentional combination of the recording and monitoring tape heads (physically located a few inches apart), which, on playback, created a gap that inadvertently produced the iconic "slap-back" effect.

Digital echo

With the advent of digital signal processing and other digital audio technologies, it has become possible to simulate almost every "echo chamber" effect by processing the signal digitally. Because digital devices are able to simulate an almost limitless variety of real reverberant spaces as well as replicate the classic tape-based echo effects, physical echo chambers fell into disuse. However, as noted above, naturally reverberant spaces such as churches continue to be used as recording venues for classical and other forms of acoustic music.

Related Research Articles

An effects unit, effects processor, or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing.

Musique concrète is a type of music composition that utilizes recorded sounds as raw material. Sounds are often modified through the application of audio signal processing and tape music techniques, and may be assembled into a form of sound collage. It can feature sounds derived from recordings of musical instruments, the human voice, and the natural environment as well as those created using sound synthesis and computer-based digital signal processing. Compositions in this idiom are not restricted to the normal musical rules of melody, harmony, rhythm, and metre. The technique exploits acousmatic sound, such that sound identities can often be intentionally obscured or appear unconnected to their source cause.

A sound effect is an artificially created or enhanced sound, or sound process used to emphasize artistic or other content of films, television shows, live performance, animation, video games, music, or other media.

Binaural recording is a method of recording sound that uses two microphones, arranged with the intent to create a 3D stereo sound sensation for the listener of actually being in the room with the performers or instruments. This effect is often created using a technique known as dummy head recording, wherein a mannequin head is fitted with a microphone in each ear. Binaural recording is intended for replay using headphones and will not translate properly over stereo speakers. This idea of a three-dimensional or "internal" form of sound has also translated into useful advancement of technology in many things such as stethoscopes creating "in-head" acoustics and IMAX movies being able to create a three-dimensional acoustic experience.

Audio feedback is a positive feedback situation that may occur when an acoustic path exists between an audio input and an audio output. In this example, a signal received by the microphone is amplified and passed out of the loudspeaker. The sound from the loudspeaker can then be received by the microphone again, amplified further, and then passed out through the loudspeaker again. The frequency of the resulting howl is determined by resonance frequencies in the microphone, amplifier, and loudspeaker, the acoustics of the room, the directional pick-up and emission patterns of the microphone and loudspeaker, and the distance between them. The principles of audio feedback were first discovered by Danish scientist Søren Absalon Larsen, hence it is also known as the Larsen effect.

Reverberation, in acoustics, is a persistence of sound after it is produced. Reverberation is created when a sound or signal is reflected. This causes numerous reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and air. This is most noticeable when the sound source stops but the reflections continue, their amplitude decreasing, until zero is reached.

<span class="mw-page-title-main">Recording studio</span> Facility for sound recording

A recording studio is a specialized facility for recording and mixing of instrumental or vocal musical performances, spoken words, and other sounds. They range in size from a small in-home project studio large enough to record a single singer-guitarist, to a large building with space for a full orchestra of 100 or more musicians. Ideally, both the recording and monitoring spaces are specially designed by an acoustician or audio engineer to achieve optimum acoustic properties.

<span class="mw-page-title-main">Multitrack recording</span> Separate recording of multiple sound sources to create a cohesive whole

Multitrack recording (MTR), also known as multitracking, is a method of sound recording developed in 1955 that allows for the separate recording of multiple sound sources or of sound sources recorded at different times to create a cohesive whole. Multitracking became possible in the mid-1950s when the idea of simultaneously recording different audio channels to separate discrete tracks on the same reel-to-reel tape was developed. A track was simply a different channel recorded to its own discrete area on the tape whereby their relative sequence of recorded events would be preserved, and playback would be simultaneous or synchronized.

The Roland Space Echo is a line of tape delay units introduced by Roland Corporation in 1974.

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A reverberation room or reverberation chamber is a room designed to create reverberation, a diffuse or random incidence sound field. Reverberation chambers tend to be large rooms and have very hard exposed surfaces. The change of impedance these surfaces present to incident sound is so large that virtually all of the acoustic energy that hits a surface is reflected back into the room. Arranging the room surfaces to be non-parallel helps inhibit the formation of standing waves - additional acoustic diffusers are often used to create more reflecting surfaces and further encourage even distribution of any particular sound field.

<span class="mw-page-title-main">Delay (audio effect)</span> Echo-like effect

Delay is an audio signal processing technique that records an input signal to a storage medium and then plays it back after a period of time. When the delayed playback is mixed with the live audio, it creates an echo-like effect, whereby the original audio is heard followed by the delayed audio. The delayed signal may be played back multiple times, or fed back into the recording, to create the sound of a repeating, decaying echo.

Gated reverb or gated ambience is an audio processing technique that combines strong reverb and a noise gate that cuts the tail of the reverb. The effect is typically applied to recordings of drums to make the hits sound powerful and "punchy" while keeping the overall mix clean and transparent sounding.

Re-amping is a process often used in multitrack recording in which a recorded signal is routed back out of the editing environment and run through external processing using effects units and then into a guitar amplifier and a guitar speaker cabinet or a reverb chamber. Originally, the technique was used mostly for electric guitars: it facilitates a separation of guitar playing from guitar amplifier processing—a previously recorded audio program is played back and re-recorded at a later time for the purpose of adding effects, ambiance such as reverb or echo, and the tone shaping imbued by certain amps and cabinets. The technique has since evolved over the 2000s to include many other applications. Re-amping can also be applied to other instruments and program, such as recorded drums, synthesizers, and virtual instruments.

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Acoustic enhancement is a subtle type of sound reinforcement system used to augment direct, reflected, or reverberant sound. While sound reinforcement systems are usually used to increase the sound level of the sound source, acoustic enhancement systems are typically used to increase the acoustic energy in the venue in a manner that is not noticed by the audience. The correctly installed systems replicate the desired acoustics of early reflections and reverberation from a room that is properly designed for acoustic music. An additional benefit of these systems is that the room acoustics can be changed or adjusted to be matched to the type of performance. The use of acoustic anhancement as electronic architecture offers a good solution for multi-use performance halls that need to be "dead" for amplified music, and are used occasionally for acoustic performances. These systems are often associated with acoustic sound sources like a chamber orchestra, symphony orchestra, or opera, but have also found acceptance in a variety of applications and venues that include rehearsal rooms, recording facilities conference rooms, sound stages, sports arenas, and outdoor venues.

In sound recording and reproduction, audio mixing is the process of optimizing and combining multitrack recordings into a final mono, stereo or surround sound product. In the process of combining the separate tracks, their relative levels are adjusted and balanced and various processes such as equalization and compression are commonly applied to individual tracks, groups of tracks, and the overall mix. In stereo and surround sound mixing, the placement of the tracks within the stereo field are adjusted and balanced. Audio mixing techniques and approaches vary widely and have a significant influence on the final product.

Send tape echo echo delay is a technique used in magnetic tape sound recording to apply a delay effect using tape loops and echo chambers.

Dereverberation is the process by which the effects of reverberation are removed from sound, after such reverberant sound has been picked up by microphones. Dereverberation is a subtopic of acoustic digital signal processing and is most commonly applied to speech but also has relevance in some aspects of music processing. Dereverberation of audio is a corresponding function to blind deconvolution of images, although the techniques used are usually very different. Reverberation itself is caused by sound reflections in a room and is quantified by the room reverberation time and the direct-to-reverberant ratio. The effect of dereverberation is to increase the direct-to-reverberant ratio so that the sound is perceived as closer and clearer.

A reverb effect, or reverb, is an audio effect applied to a sound signal to simulate reverberation. It may be created through physical means, such as echo chambers, or electronically through audio signal processing. The American producer Bill Putnam is credited for the first artistic use of artificial reverb in music, on the 1947 song "Peg o' My Heart" by the Harmonicats.

References

1 2 Huber, David Miles; Runstein, Robert E. (2005). Modern recording techniques (6th ed.). Burlington (Mass.): Focal. p. 108. ISBN 978-0-240-80625-9.
↑ Seetoo, John. "A Visit to Capitol Studios". PS Audio. PS Audio. Retrieved 7 October 2021.

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[:0-1] 1 2 Huber, David Miles; Runstein, Robert E. (2005). Modern recording techniques (6th ed.). Burlington (Mass.): Focal. p. 108. ISBN 978-0-240-80625-9.

[Seetoo-2] Seetoo, John. "A Visit to Capitol Studios". PS Audio. PS Audio. Retrieved 7 October 2021.

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