Binaural Recording

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What is Binaural Recording?

The word Binaural simply means 'relating to two ears'. Binaural recording is a method of recording audio which uses a special microphone arrangement. Typical stereo recordings are mixed for loudspeaker arrangements, and do not factor in natural crossfeed or sonic shaping of the head and ear, since these things happen naturally as a person listens, generating their own ITD's (Interaural Time Difference) and ILD's (Interaural Level Difference). Binaural recordings are made specifically for listening to with headphones, rather than speakers. There is one very important difference between headphones and speakers: the left earpiece of a pair of headphones is only audible to the left ear, whereas the left loudspeaker of a conventional stereo pair is audible to both ears, with a slight time delay and loudness difference between them. The basic concept of Binaural Recording is to capture the sounds that should be heard by the left ear, put a microphone where the left ear should be in the recording space and then do the same for the right ear. Good, convincing stereo sound is possible in both cases but for optimal results the recording must have been made, or mastered, specifically for one or the other.


History of Binaural

The first Binaural transmission was demonstrated by inventor Clement Ader, who used pairs of microphones in front of the stage of the Paris Opera, sending signals to the left and right earpieces to listeners elsewhere in the city.

The novelty of Binaural faded into obscurity due to the fact that, if binaural recordings were broadcast over airwaves at the time, the general public would need two radio's to effectively listen to the source. Binaural stayed in the background due to the expensive, specalized equipment required for quality recordings and the requirement of headphones for proper reproduction. In pre-walkman days there was very little use for headphones as people preferred to use home stereo systems to listen to audio. Recordings made in studios tend not to benefit from using a Binaural set up beyond natural crossfeed, as the spatial quality of the studio would not be very dynamic and interesting. Binaural recordings tend to be of most significance when it is capturing a live performance for example an orchestra or an environmental sound.


Why Binaural Heads Are Important?

Dummy heads are used to record sound sources, and are meant to replicate the way humans hear. A head with the right density is important. The human pinna or outer ear helps frequencies to resonate down the auditory canal at in and around 4KHZ. This can never be an exact science because of variables in size depth etc.

Binaural head recordings convey realistic spatial imagining in three dimensions when played back on headphones. This is achieved by placing two microphones inside realistic ears in the Dummy Head. Density is also very important. Every single feature of a persons face can change how a person perceives a sound, from hair, to facial structure, to how thick your head is.

A popular example of a binaural head used in studios today is the Neumann KU 100 dummy head. The dummy head is also contributed essentially as an important tool to preserve natural sounds of all kinds. In addition, the dummy head is frequently used to examine and document the influence of noise in industrial applications at various working places under realistic conditions.

In modern recordings there is very little deviation from the standard stereo sound source. Binaural recording offers a new way for the user to listen to sound sources. This is a very under used recording technique, which gives the impression of almost '3D like' sound. There are many applications for this like, museum in-ear audio tours, audiobooks, and in flight entertainment.

KU100 P.jpg Virtual Barbershop Binaural Recording (Youtube video for the Virtual Barbershop Please Use Headphones!)


Example of a Neumann Dummy head


Recording Technique

With a simple recording method, two microphones are placed seven inches (18cm) apart facing away from each other. The distance and placement roughly approximates the position of an average human's ear canals.

Using head-worn binaurals is simplicity itself - go to location, insert earbuds and start recording. The recorded stereo image will track the wearer's head movement. On playback, it can sound as if the world suddenly spins round in the opposite direction, so the recordist needs to turn their head slowly, or be prepared to edit these sections out. Likewise the "stealth concert taper" sometimes stands out with their wooden stance, while others in the audience are responding to the music.

Binaurals are omnidirectional in nature, so there is no opportunity to discriminate against sounds from particular directions, including behind the recordist. Although omnidirectional mics are usually least affected by wind noise, the binaural setup does not really favour using wind protection

Tchad Blake uses a KU 100 Dummy Head in a room with unique amplifiers and speaker systems and "processes" a signal with their electrical and acoustical properties. He uses everything from Radio Shack amplifiers to guitar amplifiers in garbage cans.

A demonstration of the recording techniques used can be seen in this video: Binaural Technique Demo - Rafael Sentoma

References

  • Entertainment Technology Press Ltd, (2002), 'Tchad Blake Recording Peter Gabriel's Upcoming Release with Neumann's KU 100 Binaural Head' [online], available: http://www.mongrell.com/tbpages/pg.htm [accessed 2 November 2010]
  • Bird vs. Alligator (2009), 'Binaural Technique Demo - Rafael Sentoma', No series title, available: http://vimeo.com/3543550 [accessed 3 November 2010]

Further Reading

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