Binaural recording is a method of recording sound that uses two microphones, arranged with the intent to create a 3-D 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.
The term "binaural" has frequently been confused as a synonym for the word "stereo", due in part to systematic misuse in the mid-1950s by the recording industry, as a marketing buzzword. Conventional stereo recordings do not factor in natural ear spacing or "head shadow" of the head and ears, since these things happen naturally as a person listens, generating interaural time differences (ITDs) and interaural level differences (ILDs) specific to their listening position. Because loudspeaker-crosstalk with conventional stereo interferes with binaural reproduction (i.e. because the sound from each channel's speaker is heard by both ears rather than only by the ear on the corresponding side, as would be the case with headphones), either headphones are required, or crosstalk cancellation of signals intended for loudspeakers such as Ambiophonics is required. For listening using conventional speaker-stereo, or MP3 players, a pinna-less dummy head may be preferable for quasi-binaural recordings such as the sphere microphone or Ambiophone. As a general rule, for true binaural results, an audio recording and reproduction system chain, from the microphone to the listener's brain, should contain one and only one set of pinnae (preferably the listener's own), and one head-shadow.
History
The history of binaural recording goes back to 1881. The first binaural unit, the théâtrophone, was invented by Clément Ader. It consisted of an array of carbon telephone microphones installed along the front edge of the Opera Garnier. The signal was sent to subscribers through the telephone system, and required that they wear a special headset, which had a tiny speaker for each ear.
The dummy head recording is associated with the use of the physical synthetic head called the “Kunstkopf”. The Kunstkopf would be placed in concert halls during the recording of a live orchestra or in the film industry actors could stand around the head whilst recording their dialogue. The dummy head could also be used to imprint positional information on prerecorded sound effects by playing sounds through a loudspeaker in a suitable orientation to the head. For example thunder and birdsong sounds to be played above the dummy head.
Within the film industry Demolition (1973) was the first radio drama recorded using a dummy head.
In 1974 Virgin Records issued the first solo album by Tangerine Dream's leader Edgar Froese, titled Aqua. The brief sleeve notes inform listeners that side 2 of the disc (i.e. the tracks NGC 891 and Upland) were recorded using the artificial head system developed by Gunther Brunschen. Listeners were advised to optimize their listening by using stereo headphones for that side of the album.
Although Edgar was keen to continue to use and promote this system for subsequent recordings, it was abandoned, due to the fact that, although it worked well through headphones, the improved sound quality did not translate adequately through a hi-fi speaker system.
In 1978, Lou Reed released the first commercially produced binaural pop record, Street Hassle, a combination of live and studio recordings.
Binaural stayed in the background due to the expensive, specialized equipment required for quality recordings, and the requirement of headphones for proper reproduction. Particularly in pre-Walkman days, most consumers considered headphones an inconvenience, and were only interested in recordings that could be listened to on a home stereo system or in automobiles. Lastly, the types of things that can be recorded do not have a typically high market value. Studio recordings would have little to benefit from using a binaural set up, beyond natural cross-feed, as the spatial quality of the studio would not be very dynamic and interesting. Recordings that are of interest are live orchestral performances, and ambient "environmental" recordings of city sounds, nature, and other such subject matters.