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An echo chamber is a hollow enclosure used to produce reverberated 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 large room or a cave; these effects might be accomplished by playing the recording of the conversation inside an echo chamber, with an accompanying microphone to catch the reverberation. Nowadays, digital, algorithmic, and convolution reverbs are more widely used to create such effects, but echo chambers are still used today, such as the famous echo chambers at Capitol Studios. 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; these were deliberately built to create internal reflections in order to enhance and project sound from the stage in the days before electrical amplification. Sometimes echo effects were the unintentional side effect of the architectural or engineering design, such as for the Hamilton Mausoleum in Scotland, reportedly having the longest reverberation of any building. ==Electro-acoustic echo chambers== 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. 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/reverberation chambers was important for sound recording because of the limitations of early recording systems. Except in the case of live performances, most commercial popular recordings were 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 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 reverberation-free sound of early recordings unappealing. Consequently, record producers and engineers quickly came up with a very effective method of adding 'artificial' reverberation/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 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) will pick 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 the late Clive Robinson, who was site foreman at the time of construction. His construction and engineering team 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 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. 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, 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 ''L.A. Woman''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「echo chamber」の詳細全文を読む スポンサード リンク
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