Binaural recording

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.

[1] It consisted of an array of spaced pairs of carbon pencil microphones installed along the front edge of the Opera Garnier.

One, referred to as "Oscar" was made by Bell Labs, using 1.4 in (36 mm) microphones inserted into the cheeks of a mannequin's head, and was demonstrated at the World Fair in Chicago, in 1933.

The Dutch firm, Philips, also developed a binaural head, with the microphones located at the ears, which produced a better result.

[3] Their use ranged from acoustic analysis, such as to record word scoring for speech intelligibility measurement,[4] hearing aid design,[5] for music reproduction, and radio drama.

[6] In 1974, Virgin Records issued the first solo album by Tangerine Dream's leader Edgar Froese, titled Aqua.

The sleeve notes inform listeners that the tracks NGC 891 and Upland were recorded using a binaural head system developed by Gunther Brunschen.

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.

During the 1990s, electronic devices which used digital signal processing (DSP) to reproduce HRTFs were made commercially available.

In 2005, Aqua was remixed for limited edition reissue in Germany and Japan, with an additional track Upland Dawn appended to the end of the CD.

The show toured the world, and played on Broadway for several months, winning a Tony Award for its sound design.

[10] Binaural sound is often used in Virtual Reality, to help the user locate the source of something outside their field of vision.

A smart phone, tablet or computer can be used to listen to these with headphones and the music track will be rendered into binaural sound on playback.

The aim is that each microphone records sound in the same spatial relationship: each signal having the relative inter-aural time, level and timbral differences that the two ears of a human being would have if they were situated in the same position as the binaural head.

Our brains are then able to interpret the spatial cues within the recordings to create a three-dimensional soundscape within our consciousness[18] because it mirrors our own hearing system.

Using an MRI scanner, Brüel & Kjær and DTU collected the geometries of a large population of human ears.

The binaural head, or microphone, is therefore theoretically making a recording of how humans will hear multi-channel content.

The problem arises that each human head has different shaped and sized features, making it very difficult to create a binaural effect compatible for everyone's ears.

At the start of each variation, the listener would hear a series of test signals allowing for a choice of which version gives them the best spatial experience.

[citation needed] The issue of timbral coloration is mentioned in a large amount of spatial enhancement research and is sometimes seen as the outcome of the misuse or insufficient amount of HRTF data when reproducing binaural audio for example, or the fact that the end-user simply will not respond well to the collected HRTF data.

The HRTFs used for Private Peaceful[31] were designed by measuring impulse responses in a reverberant room, done so to capture a sense of space, but is not very external and there are obvious timbral issues as pointed out by Pike.

[citation needed] Juha Merimaa from Sennheiser Research Laboratories found that using HRTF filters to reduce timbral issues did not affect the spatial localization previously achieved using the data when tested on a panel of listeners.

But many people may only have access to low quality headphones, which can result in them hearing something very different from what was intended, and that can muddy the spatial cues in the binaural audio.