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.
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.
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.
[2] 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.
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.
Users can ostensibly watch 360° films and music with the immersive surround sound experience remaining intact despite using just the two headset speakers.
Notably, any full 360° multi-channel soundtrack is automatically converted to simulated binaural audio when listened to with headphones.
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.
There are two main methods used to create a binaural effect: A typical binaural recording unit has two high-fidelity microphones mounted in a dummy head, inset in ear-shaped molds to fully capture all of the audio frequency adjustments (known as head-related transfer functions (HRTFs) in the psychoacoustic research community) that happen naturally as sound wraps around the human head and is "shaped" by the form of the outer and inner ear.
The main focus of recording with a dummy head is to achieve a perfect binaural playback that is suited to all listeners.
Therefore, the simulated dummy head recording algorithm uses average HRTFs to create a moderate binaural effect for everyone.
In 1959, an echo chamber was famously used by Irving Townsend during the post-production process of Miles Davis's 1959 album Kind of Blue.
At 30th Street, a line was run from the mixing console down into a low-ceilinged, concrete basement room—about 12 by 15 feet in size—anywhere we set up a speaker and a good omnidirectional microphone.
The soundtrack to a film, for example, will be recorded by the binaural microphone with all the environmental cues of the given location, as well as reverberations, including those commonly created by the human torso (assuming a HATS[13] model is used).
[14] Using an MRI scanner, Brüel & Kjær and DTU collected the geometries of a large population of human ears.
Based on this, High-frequency Head and Torso Simulator (HATS) Type 5128, creates a very realistic reproduction of the acoustic properties, covering the full audible frequency range (up to 20 kHz).
The diffuse-field head-transfer function (HRTF), that is, the frequency response at the eardrum averaged for sounds coming from all possible directions, is quite grotesque, with peaks and dips exceeding 10 dB.
[19] 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[18] 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.
[19] 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.
As previously discussed, there are issues of timbral effects present while using BRIR and HRTF data to create spatially improved audio, techniques used by Chris Pike and BBC R&D.
"[Are timbral issues brought about by the use of BRIR and HRFT data] any worse than the difference between some cheap headphones that you get with an mp3 player versus some nice Sennheisers".
