Binaural recording

Binaural recording

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Binaural recording is a method of recording
Recording
Recording is the process of capturing data or translating information to a recording format stored on some storage medium, which is often referred to as a record or, if an auditory medium, a recording....

 sound that uses two microphone
Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...

s, arranged with the intent to create a 3-D
Three-dimensional space
Three-dimensional space is a geometric 3-parameters model of the physical universe in which we live. These three dimensions are commonly called length, width, and depth , although any three directions can be chosen, provided that they do not lie in the same plane.In physics and mathematics, a...

 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
Dummy head recording
In acoustics, dummy head recording is a method used to make binaural recordings, that allow a listener wearing headphones to perceive the directionality and the room acoustics of single or multiple sources.Human perception of the direction of a sound source is complex, and consists of:#Simple...

", wherein a mannequin
Mannequin
A mannequin is an often articulated doll used by artists, tailors, dressmakers, and others especially to display or fit clothing...

 head is outfitted with a microphone in each ear. Binaural recording is intended for replay using headphones and will not translate properly over stereo speakers.

The term "binaural" has frequently been confused as a synonym for the word "stereo
Stereophonic sound
The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...

", and this is partially due to a large amount of misuse in the mid-1950s by the recording industry, as a marketing
Marketing
Marketing is the process used to determine what products or services may be of interest to customers, and the strategy to use in sales, communications and business development. It generates the strategy that underlies sales techniques, business communication, and business developments...

 buzzword
Buzzword
A buzzword is a term of art, salesmanship, politics, or technical jargon that is used in the media and wider society outside of its originally narrow technical context....

. 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 their own ITDs
Interaural time difference
The interaural time difference when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localisation of sounds, as it provides a cue to the direction or angle of the sound source from the head. If a signal arrives at the head from one...

 (interaural time differences) and ILDs (interaural level differences). Because loudspeaker-crosstalk of conventional stereo interferes with binaural reproduction, either headphones are required, or crosstalk cancellation of signals intended for loudspeakers such as Ambiophonics
Ambiophonics
Ambiophonics is a method in the public domain that employs digital signal processing and two loudspeakers directly in front of the listener in order to improve reproduction of stereophonic and 5.1 surround sound for music, movies, and games in home theaters, gaming PCs, workstations, or studio...

. For listening using conventional speaker-stereo, or mp3 players, a pinna-less dummy head may be preferable for quasi-binaural recording, such as the sphere microphone or Ambiophone
Ambiophonics
Ambiophonics is a method in the public domain that employs digital signal processing and two loudspeakers directly in front of the listener in order to improve reproduction of stereophonic and 5.1 surround sound for music, movies, and games in home theaters, gaming PCs, workstations, or studio...

. As a general rule, for true binaural results, an audio recording and reproduction system chain, from microphone to listener's brain, should contain one and only one set of pinnae (preferably the listener's own) and one head-shadow.

Examples


Recording technique


With a simple recording method, two microphones are placed 18 cm (7") apart facing away from each other. This method will not create a real binaural recording. The distance and placement roughly approximates the position of an average human's ear canal
Ear canal
The ear canal , is a tube running from the outer ear to the middle ear. The human ear canal extends from the pinna to the eardrum and is about 35 mm in length and 5 to 10 mm in diameter....

s, but that is not all that is needed. More elaborate techniques exist in pre-packaged forms. A typical binaural recording unit has two high-fidelity microphones mounted in a dummy
Dummy
Dummy may refer to:*Military dummy:**dummy round—a cartridge that is inert, i.e. contains neither primer nor gunpowder**decoy—fake military equipment intended to deceive the enemy...

 head, inset in ear-shaped molds
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....

 to fully capture all of the audio frequency
Audio frequency
An audio frequency or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human...

 adjustments (known as head-related transfer function
Head-related transfer function
A head-related transfer function is a response that characterizes how an ear receives a sound from a point in space; a pair of HRTFs for two ears can be used to synthesize a binaural sound that seems to come from a particular point in space. Some consumer home entertainment products designed to...

s (HRTFs) in the psychoacoustic research
Psychoacoustics
Psychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound...

 community) that happen naturally as sound wraps around the human head and is "shaped" by the form of the outer and inner ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....

. The Neumann KU-81, and KU-100 are the most commonly used binaural packages, especially by musicians. The KEMAR system is another alternative. It was presented already in 1972 as a research mannequin for in-situ testing of hearing aids. The HEAD acoustics aachenhead unit (HMS IV) provides different equalization interfaces, either to make signals compatible with loudspeaker reproduction or to allow for comparison of signals with standard microphone recordings. Other alternatives are the Brüel & Kjær
Brüel & Kjær
Brüel & Kjær is a subsidiary of UK-based Spectris plc. Brüel & Kjær is a manufacturer and supplier of sound and vibration measurement apparatus. The company headquarters is based in Nærum, Denmark...

 and the 01dB-Metravib mannequins. A simplified version of binaural recordings can be achieved using microphones with a separating element, like the Jecklin Disk
Jecklin Disk
A Jecklin Disk is a sound-absorbing disk placed between two microphones to create an acoustic "shadow" from one microphone to the other. The resulting two signals can possibly produce a pleasing stereo effect...

. It used a 30 cm (11.81") acoustically-absorptive disk between the mics, spaced 18 centimeters. Now the new Disk is 35 cm in diameter and has a spacing of the microphones of 36 cm (double head). Nevertheless, not all cues required for exact localization of the sound sources can be preserved this way, but it works also well for loudspeaker reproduction.

In the late 1960s, Aiwa and Sony offered headphones with a pair of microphones mounted on the headband. around two-inches above the ears. These allowed pseudo-binaural recordings to be made.

Miniature binaural "in-ear" or "near-ear" microphones can be linked to a portable Digital Audio Tape (DAT) or MiniDisc recorder, bypassing the need for a dummy head by using the recordist's own head. The first clip-on binaural microphones using the recordist's own head were offered by Core Sound LLC
Core Sound LLC
Core Sound LLC is an audio equipment manufacturer of microphones and audio electronics, primarily addressing portable recording and microphones designed using psychoacoustic principles. Founded in 1989, it is a manufacturer of binaural microphones for binaural recording...

 in 1989. The first completely "in-ear" binaural microphones using the recordist's own head were offered by Sound Professionals
Sound Professionals
The Sound Professionals, Inc. is a manufacturer of professional and consumer microphones and audio electronics, primarily for portable audio recording. Created in 1997, they are one of a small number of manufacturers of binaural and other types of microphones for binaural recording...

 in 1999.

Playback


Once recorded, the binaural effect can be reproduced using headphones or a dipole stereo. It does not work with mono
Monaural
Monaural or monophonic sound reproduction is single-channel. Typically there is only one microphone, one loudspeaker, or channels are fed from a common signal path...

 playback; nor does it work while using loudspeaker units, as the acoustics of this arrangement distort the channel separation via natural crosstalk (an approximation can be obtained if the listening environment is carefully designed by employing expensive crosstalk cancellation equipment.)

The result is a listening experience that spatially transcends normally recorded stereo, since it accurately reproduces the effect of hearing a sound in person, given the 360° nature of how human ears pick up nuance in the sound waves. Binaural recordings can very convincingly reproduce location of sound behind, ahead, above, or wherever else the sound actually came from during recording.

Any set of headphones that provide good right and left channel isolation are sufficient to hear the immersive effects of the recording, and anyone who has even a cheap set of headphones can enjoy the recordings. Several high-end head set manufacturers have created some units specifically for the playback of binaural. Etymotic Research
Etymotic Research
Etymotic Research is a United States audio company specializing in the research, design, and production of high fidelity in-ear products. It is notable for being one of the earliest and foremost manufacturers of canalphones for consumer use....

's ER-4B canal phone actually sits inside the ear, much like a hearing aid
Hearing aid
A hearing aid is an electroacoustic device which typically fits in or behind the wearer's ear, and is designed to amplify and modulate sound for the wearer. Earlier devices, known as "ear trumpets" or "ear horns", were passive funnel-like amplification cones designed to gather sound energy and...

. The B model is tuned and equalized to enhance binaural playback. In addition, a number of headphone amplifier companies have created hardware that takes advantage of these special recordings. However, these in-ear-canal phones tend to suffer from poor externalization i.e. inside-head localization. It is also found that even normal headphones suffer from poor externalization, especially if the headphone completely blocks the ear from outside. A better design for externalization found in experiments is the open-ear one, where the drivers are sitting in front of the pinnae with the ear canal connected to the air. The hypothesis is that when the ear canal is completely blocked, the radiation impedance
Radiation impedance
In acoustics, radiation impedance is the impedance of any vibrating solid or fluid that radiates sound in the surrounding medium.-See also:*Acoustic impedance...

 seen from the eardrum to the outside has been altered, which negatively affects externalization.

There are some complications with the playback of binaural recordings through normal headphones. The sound that is picked up by a microphone placed in or at the entrance of the ear channel has a frequency spectrum that is very different from the one that would be picked up by a free-standing microphone. The diffuse-field head-transfer function, that is, the frequency response at the ear drum averaged for sounds coming from all possible directions, is quite grotesque, with peaks and dips of 10 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

. Frequencies around 5 kHz in particular are strongly attenuated as compared to side-presentation. If headphones were designed to have a flat response, then they would sound much too 'bright' when used to listen to stereo recordings and for this reason, most headphones are designed to have a notch around 5 kHz. This can only ever approximate to a particular listener's ears, meaning that there can be no such thing as a 'flat' pair of headphones - they have to match the listener's ears, unlike speakers which aim to produce a flat free field response. For binaural listening though, the headphones need to have a flat response to the ear-canal entrance (not the eardrum) since it is at the ear-canal entrance that the recording microphones are placed. While it is in theory possible to equalise any headphones for a flat response at the entrance, a better approach is to use headphones designed without the notch in the first place.

The fact that most headphones are actually designed to have a notch in the 5 kHz region is not widely understood, and this may have led to errors in the assessment of binaural recordings, since flat headphones are not normally available, and 'high quality' headphones incorporate the notch just like any others, though perhaps with a better approximation to that needed by the average ear. Male and female ears are of course different in size, and the outer ear gets bigger with increasing age, raising the possibility that most headphones are only really suited to young men. If headphones were designed to be flat, with a choice of equalisations available in headphone amplifiers, then headphone listening could be a more controlled experience, whether in binaural or stereo mode.

History


The history of binaural recording goes back to 1881. The first binaural unit, the Théâtrophone
Théâtrophone
Théâtrophone was a telephonic distribution system that allowed the subscribers to listen to opera and theatre performances over the telephone lines. The théâtrophone evolved from a Clément Ader invention, which was first demonstrated in 1881, in Paris...

, was an array of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 microphones installed along the front edge of the Opera Garnier
Palais Garnier
The Palais Garnier, , is an elegant 1,979-seat opera house, which was built from 1861 to 1875 for the Paris Opera. It was originally called the Salle des Capucines because of its location on the Boulevard des Capucines in the 9th arrondissement of Paris, but soon became known as the Palais Garnier...

. The signal was sent to subscribers through the telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 system, and required that they wear a special head set, which had a tiny speaker for each ear.

The novelty wore off, and there wasn't significant interest in the technology
Technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...

 until around forty years later when a Connecticut radio station
Radio station
Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...

 began to broadcast binaural shows. Stereo radio had not yet been implemented, so the station actually broadcast the left channel on one frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 and the right channel on a second. Listeners would then have to own two radios, and plug the right and left ear pieces of their head sets into each radio. Naturally, the expense of owning two radios was, at the time, too much for a broad audience, and again binaural faded into obscurity.

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
Walkman
Walkman is a Sony brand tradename originally used for portable audio cassette, and now used to market Sony's portable audio and video players as well as a line of Sony Ericsson mobile phones...

 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
Market value
Market value is the price at which an asset would trade in a competitive auction setting. Market value is often used interchangeably with open market value, fair value or fair market value, although these terms have distinct definitions in different standards, and may differ in some...

. Recordings that are done in studio
Studio
A studio is an artist's or worker's workroom, or the catchall term for an artist and his or her employees who work within that studio. This can be for the purpose of architecture, painting, pottery , sculpture, scrapbooking, photography, graphic design, filmmaking, animation, radio or television...

s 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.

The modern era has seen a resurgence of interest in binaural, specifically within the audiophile
Audiophile
An audiophile is a person who enjoys listening to recorded music, usually in a home. Some audiophiles are more interested in collecting and listening to music, while others are more interested in collecting and listening to audio components, whose "sound quality" they consider as important as the...

 community, partially due to the widespread availability of headphones, and cheaper methods of recording. A small grassroots
Grassroots
A grassroots movement is one driven by the politics of a community. The term implies that the creation of the movement and the group supporting it are natural and spontaneous, highlighting the differences between this and a movement that is orchestrated by traditional power structures...

 movement of people building their own recording sets and swapping them on the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 has joined the very few CDs available for purchase.

In the late 1970s, Lou Reed
Lou Reed
Lewis Allan "Lou" Reed is an American rock musician, songwriter, and photographer. He is best known as guitarist, vocalist, and principal songwriter of The Velvet Underground, and for his successful solo career, which has spanned several decades...

 recorded 3 albums in binaural: Street Hassle
Street Hassle
Street Hassle is the eighth solo album by Lou Reed, originally released by Arista Records. The album is notable as the first commercially released pop album to employ binaural recording technology. Street Hassle combines live concert tapings and studio recordings.The album is also notable for...

, Live: Take No Prisoners
Live: Take No Prisoners
Live: Take No Prisoners is Lou Reed's third live album. Released in 1978, it was Reed's contribution to the double live album era. It was recorded at the Bottom Line in New York, and there is no overdubbing...

, and The Bells
The Bells (album)
The Bells is the ninth album by Lou Reed, released through Arista Records in 1979. It is recorded in binaural sound. "City Lights" is a tribute to Charlie Chaplin. "Disco Mystic" is indeed played in a disco style, and the lyrics consist of those two words repeated...

. In 2000, the American rock band Pearl Jam
Pearl Jam
Pearl Jam is an American rock band that formed in Seattle, Washington, in 1990. Since its inception, the band's line-up has included Eddie Vedder , Jeff Ament , Stone Gossard , and Mike McCready...

 released an album titled Binaural
Binaural (album)
Binaural is the sixth studio album by the American alternative rock band Pearl Jam, released on May 16, 2000 through Epic Records. Following a full-scale tour in support of its previous album, Yield , Pearl Jam took a short break before reconvening toward the end of 1999 to commence work on a new...

, in which the binaural recording method was used for some tracks.

The additional content present on the DVD release of Monsters, Inc.
Monsters, Inc.
Monsters, Inc. is a 2001 American computer-animated film and the fourth feature-length film produced by Pixar Animation Studios. It was directed by Pete Docter, co-directed by Lee Unkrich and David Silverman, and written by Jill Culton, Peter Docter, Ralph Eggleston, Dan Gerson, Jeff Pidgeon, Rhett...

 includes a practical presentation of binaural recording, featuring a Pixar
Pixar
Pixar Animation Studios, pronounced , is an American computer animation film studio based in Emeryville, California. The studio has earned 26 Academy Awards, seven Golden Globes, and three Grammy Awards, among many other awards and acknowledgments. Its films have made over $6.3 billion worldwide...

 sound engineer and actors John Goodman
John Goodman
John Stephen Goodman is an American film, television, and stage actor. He is best known for his role as Dan Conner on the television series Roseanne for which he won a Best Actor Golden Globe Award in 1993, and for appearances in the films of the Coen brothers, with prominent roles in Raising...

 and Billy Crystal
Billy Crystal
William Edward "Billy" Crystal is an American actor, writer, producer, comedian and film director. He gained prominence in the 1970s for playing Jodie Dallas on the ABC sitcom Soap and became a Hollywood film star during the late 1980s and 1990s, appearing in the critical and box office successes...

.

In 2004, many lacquer masters were discovered in the vaults of Sony Music Studios in New York which consisted of recordings that Leopold Stokowski
Leopold Stokowski
Leopold Anthony Stokowski was a British-born, naturalised American orchestral conductor, well known for his free-hand performing style that spurned the traditional baton and for obtaining a characteristically sumptuous sound from many of the great orchestras he conducted.In America, Stokowski...

 and his All-American Youth Orchestra had made for Columbia Records in Hollywood in the summer of 1941. These lacquers had been recorded in pairs, on two separate turntables, one being a safety back-up to the other in case something went wrong with the subsequent dubbing to 78rpm discs. Significantly, the pairs of lacquers were labelled "Left" and "Right" respectively, rather than "A and "B" as was usually the case. It was also usually the case in 78rpm recordings that the same microphone source fed each of the two turntables. However, these labelling differences led to a couple of experiments whereby the "Left" and "Right" lacquers of two recordings were painstakingly synchronised. These experiments proved that for these sessions two separate microphones had been used, placed near each other and each leading to its own turntable, with binaural sound being the result when synchronised. The two binaural recordings were made available to the Leopold Stokowski Society and both have now been released on CD: Wagner's Ride of the Valkyries
Ride of the Valkyries
The Ride of the Valkyries is the popular term for the beginning of Act III of Die Walküre, the second of the four operas by Richard Wagner that comprise Der Ring des Nibelungen. The main theme of the Ride, the leitmotif labelled Walkürenritt, was first written down by the composer on 23 July 1851...

 on Cala Records CACD0549 and the 'Scherzo' from Mendelssohn's Midsummer Night's Dream on Cala Records CACD0551.

In 2009, the BBC Radio 7 science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 drama
Drama
Drama is the specific mode of fiction represented in performance. The term comes from a Greek word meaning "action" , which is derived from "to do","to act" . The enactment of drama in theatre, performed by actors on a stage before an audience, presupposes collaborative modes of production and a...

 Planet B
Planet B
Planet B is a science fiction drama series first broadcast on BBC Radio 7 on 2 March 2009 as part of BBC Radio's science fiction season between February and March 2009. Planet B is set in a virtual world called "Planet B" in which people play as life-size avatars...

 used an online binaural advert in order to promote the programme's second series.
There are several games for the iPhone which use binaural audio. These include Zen Bound from developer Secret Exit, and Aves by Action = Reaction Games. In its April 2010 issue, the UK edition of Wired magazine covered Papa Sangre from developer Somethin' Else, a "video game with no video" created entirely in binaural audio and which claims to be the first iPhone game to have an engine that can create binaural audio in real time by processing sound sources using an HRTF
Head-related transfer function
A head-related transfer function is a response that characterizes how an ear receives a sound from a point in space; a pair of HRTFs for two ears can be used to synthesize a binaural sound that seems to come from a particular point in space. Some consumer home entertainment products designed to...

.

See also

  • Alan Blumlein
    Alan Blumlein
    Alan Dower Blumlein was a British electronics engineer, notable for his many inventions in telecommunications, sound recording, stereo, television and radar...

  • Ambiophonics
    Ambiophonics
    Ambiophonics is a method in the public domain that employs digital signal processing and two loudspeakers directly in front of the listener in order to improve reproduction of stereophonic and 5.1 surround sound for music, movies, and games in home theaters, gaming PCs, workstations, or studio...

     – binaural with speakers, not headphones
  • Binaural tones
  • Environmental audio extensions
    Environmental audio extensions
    The environmental audio extensions are a number of digital signal processing presets for audio, present in Creative Technology's later Sound Blaster sound cards and the Creative NOMAD/Creative ZEN product lines...

  • Field Recording
    Field recording
    Field recording is the term used for an audio recording produced outside of a recording studio. The recording is typically recorded in the same channel format as the desired result, for instance, stereo recording equipment will yield a stereo product...

  • Head-related transfer function
    Head-related transfer function
    A head-related transfer function is a response that characterizes how an ear receives a sound from a point in space; a pair of HRTFs for two ears can be used to synthesize a binaural sound that seems to come from a particular point in space. Some consumer home entertainment products designed to...

  • Holophonics
    Holophonics
    Holophonics is a binaural recording system created by Hugo Zuccarelli that is claimed to be based on the claim that the auditory system acts as an interferometer. The sound characteristics of Holophonics are most clearly heard through headphones, though can be demonstrated to be effective with 2...

  • Psychoacoustics
    Psychoacoustics
    Psychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound...

  • QSound
  • SRS Labs
    SRS Labs
    SRS Labs, Inc. , is a Santa Ana, California-based audio technology engineering company that specializes in audio enhancement solutions for wide variety of consumer electronic devices. Originally a part of Hughes Aircraft Company, the audio division developed the Sound Retrieval System technology,...

  • Stereophonic sound
    Stereophonic sound
    The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...

  • Tchad Blake
    Tchad Blake
    Tchad Blake is an American record producer, audio engineer, mixer and musician.He has worked with numerous artists and musicians, including State Radio, Apartment 26, Elvis Costello, Peter Gabriel, Pearl Jam, Tom Waits, Richard Thompson, Brazilian Girls, Sheryl Crow, November 2nd, Travis, Marike...

  • Théâtrophone
    Théâtrophone
    Théâtrophone was a telephonic distribution system that allowed the subscribers to listen to opera and theatre performances over the telephone lines. The théâtrophone evolved from a Clément Ader invention, which was first demonstrated in 1881, in Paris...


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