Echo chamber

From Academic Kids

This article is about the technological device. For other meanings, see Vast right-wing conspiracy.

When used literally, the term echo chamber refers to a hollow enclosure used to produce echoing sounds, usually for recording purposes. For example, the producers of a television or radio program might wish to produce the aural illusion that a conversation is taking place in a cave; this effect might be accomplished by playing the recording of the conversation inside an echo chamber, with an accompanying microphone to catch the echoes.

In music, the use of acoustic echo and reverberation effects has taken many forms and dates back many hundreds of years. Medieval and Renaissance sacred music 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, structures that were deliberately built to create internal echoes in order to enhance and project sound from the stage in the days before electrical amplification.

Contents

Electro-acoustic echo chambers

Development 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.

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 a hard material (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.

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

Because virtually every sound we hear in everyday life is a complex mixture of both the source sound and its echoes and reverberations, audiences not surprisingly found the totally 'dry' and echo-free sound of early recordings unappealing. Consequently, record producers and engineers quickly came up with a very effective method of adding 'artificial' echo which could, in the hands of experts, be controlled with a remarkable degree of accuracy.

Producing echo and reverberation in this form of echo chamber is remarkably 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 echo chamber. One or more microphones are placed along the length of the room and these pick up both the sound from the speaker and the echoes of it that bounce off the walls of the chamber. The further away from the speaker, the more echo and reverberation the microphone/s will pick up and the louder the echo becomes in relation to the source. The signal from microphone line is then fed back to the mixing desk, where the echo-enhanced sound can be blended with the original 'dry' input.

An excellent example of the creative use 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 in London was one of the first in the world to be specially built for recording purposes, when the studio 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 for the recording of 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 favoured recording venue of the Montreal Symphony Orchestra and many others, and is much sought after for classical recordings because of its unique acoustic characteristics. Likewise, the distinctive reverberation on the early hit records by Bill Haley & The Comets was created by recording the band under the domed ceiling of Decca's studio in New York, 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, tiled bathrooms and toilets 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 toilet -- a tactic also used by The Doors for the recording of their 1970 album LA Woman.

Electronic echo chambers and echo machines

In the 1950s and '60s, 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. In domestic tape recorders, it is usually not possible to have both the record and playback heads activated at the same time, but tape echo machines are specially constructed to allow this.

When a signal from a voice or instrument is fed into the machine, it records the signal onto the tape loop as it passed over the record head. As the tape travels on, 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 at which the tape loop moves 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 very distinctive 'feedback' effect that adds more and more noise to the loop with each repeat; if fully activated, this control will ultimately produce a continuous feedback loop of pure noise.

Tape echo that has few repeats and a very short delay between each repeat is often referred to as '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.

Oil-can delay method

An alternative echo system was the so-called "oil-can delay" method. Tape delays and oil-can delays work on the same basic electrical principle -- that of encoding voltage variations in some from of magnetic storage medium -- but they differ in the choice of storage medium.

The 'oil-can' method uses a rotating capacitor made of an insulating material (e.g. rubber ) in the form of a belt or drum, which can store electromagnetic charge on its surface. The capacitor is housed within a container of insulating liquid such as mineral oil; as it rotates, its surface is touched by an array of fine metal brushes which are connected to the audio source signal and the capacitor 'records' a representation of the voltage variations onto its surface, which are then picked up by 'playback' brushes mounted further around the assembly. The oil acts as an insulator, preventing the tiny charge from dissipating into the air.

Digital echo

With the advent of digital signal processing and other digital audio technologies, it became possible to simulate almost every "echo chamber" effect by processing the signal digitally. Because they are able to simulate an almost limitless variety of real reverberant spaces, as well as replicating the classic tape-based echo effects, physical echo chambers fell into disuse although, as noted above, the use of naturally reverberant spaces such churches as recording venues continues in classical and other forms of acoustic music.

As a metaphor

Metaphorically, the term echo chamber can refer to any situation in which information or ideas are amplified by transmission inside an enclosed space.

For example, observers of journalism in the mass media describe an echo chamber effect in media discourse. One purveyor of information will make a claim, which many like-minded people then repeat, overhear, and repeat again (often in an exaggerated or otherwise distorted form) until most people assume that some extreme variation of the story is true.

References

R.G. Keen: The Technology of Oil Can Delays http://www.geofex.com/Article_Folders/oil_can_delays.htm

Echo Chamber - Disinfopedia http://www.disinfopedia.org/wiki.phtml?title=Echo_chamber

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