Holophonics is a binaural recording system created by Hugo Zuccarelli that is 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 channel stereo speakers, as long as they are phase coherent. Zuccarelli's company, Acoustic Integrity, also sells loudspeakers under the Holophonics brand.
There has been some controversy over the claims made by Hugo Zucharelli regarding this recording technique. The effects achieved are comparable to traditional binaural recording using mannequin heads, or via more traditional 3D audio techniques via HRTF's. There is no evidence nor studies conducted that indicate that the Holophonic technique is substantially different from or superior to these methods, nor has Zucharelli ever published his technique, nor has he allowed independent study of the results. The only available publication is a patent[1], which describes a fairly typical dummy-head binaural recording.
While otoacoustic emissions do exist, there is no evidence to support the assertion that these play a role in sound localization, nor is any mechanism for this "interference" effect claimed by Zucharelli supported. On the contrary, there is abundant literature proving that properly presented spatial cues via HRTF synthesis (mimicking binaural heads) or binaural recording is adequate to reproduce realistic spatial recordings comparable to real listening, and comparable to the Holophonics demonstrations.[2]
Holophonics was created by Argentine Hugo Zuccarelli in 1980, during his studies at the Politecnico di Milano university. In 1983 Zuccarelli released a recording entitled Zuccarelli Holophonics (The Matchbox Shaker) the UK by CBS which consisted entirely of short recordings of sound effects designed to show off the system. These included the shaking matchbox, haircut & blower, bees, balloon, plastic bag, birds, airplanes, fireworks, thunder, and racing cars. In its early years, Holophonics was used by various artists including Pink Floyd (The Final Cut, 1984), Roger Waters solo album (The Pros and Cons..., 1985), Psychic TV (Dreams Less Sweet, 1983). It has been used in film soundtrack, popular music, television and themeparks.[3]
Zuccarelli states that the human auditory system is a sound emitter, producing a reference sound that combines with incoming sound to form an interference pattern inside the ear. The nature of this pattern is sensitive to the direction of the incoming sound. According to the hypothesis, the cochlea detects and analyzes this pattern as if it were an acoustic hologram. The brain then interprets this data and infers the direction of the sound. An article from Zuccarelli presenting this theory was printed in the magazine New Scientist in 1983. This article was soon followed by two letters, casting doubt on Zuccarelli's theory and his scientific abilities.[4][5]
To date, there has been no evidence provided that any acoustic emissions are used for sound localization. Holophonics, like binaural recording, instead reproduces the interaural differences (arrival time and amplitude between the ears), as well as rudimentary head-related transfer functions (HRTF). These create the illusion that sounds produced in the membrane of a speaker emanate from specific directions.