Holophonics

Holophonics is a binaural recording and reproduction system created by the Argentine inventor Hugo Zuccarelli in 1980, during his studies at the Politecnico di Milano. The source dossier describes it as "a binaural recording system ... based on the claim that the human auditory system acts as an interferometer." It relies on phase variance, as stereophonic sound does. The word "holophonics" is related to "acoustic hologram."

Claimed mechanism

Zuccarelli's stated theory is that the human auditory system is a sound emitter: it produces a reference sound that combines with incoming sound to form an interference pattern inside the ear, whose nature is sensitive to the direction of the incoming sound. Under the hypothesis, the cochlea detects and analyzes this pattern as if it were an acoustic hologram, and the brain interprets the data to infer direction. See Auditory Interferometer Hypothesis.

What the dossier says actually explains it

The dossier's Wikipedia-derived text does not endorse the interferometer theory. It states that "to date, there has been no evidence provided that any acoustic emissions are used for sound localization," and that Holophonics, like Binaural Recording, instead reproduces the interaural differences (arrival time and amplitude between the ears) as well as rudimentary Head-Related Transfer Function (HRTF) cues. These create the illusion that sounds produced in a speaker membrane emanate from specific directions.

The dossier further states that while Otoacoustic Emissions do exist, there is no evidence they play a role in sound localization, and no mechanism for the claimed interference effect is supported. It cites abundant literature showing that properly presented spatial cues via HRTF synthesis or binaural recording are adequate to reproduce realistic spatial recordings comparable to real listening — and comparable to the Holophonics demonstrations.

The practical distinction the dossier implies is therefore: the demonstrations are comparable to what binaural recording and HRTF synthesis already achieve; the theory attached to them is unsupported.

Listening conditions

The dossier states that Holophonics' sound characteristics are most clearly heard through headphones, though they can be effectively demonstrated with two-channel stereo speakers provided those speakers are phase-coherent.

The head-shaped microphone

The concrete artifact behind the system is a head-shaped acoustic monitoring device, described in two Zuccarelli patents:

• US4680856 — Process for Forming an Acoustic Monitoring Device — Process for forming an acoustic monitoring device. A human-head-shaped device reproducing the auricles, auditory meatus, Eustachian tubes, and nasal and oral cavities, with membranes at the eardrum positions coupled to acoustic members that output electrical signals. Manufactured by a multi-stage molding process using liquid silicone rubber.
• EP0050100 — Device for the Spatial Codification of Sounds — Device for the spatial codification of sounds. A head-shaped microphonic support with auricles and internal cavities, a wig providing asymmetry for front/back discrimination, and two microphones in the meatus cavity at the exact position and orientation of the eardrum, communicating at the back with Eustachian-tube cavities; the oral cavity is open to the outside.

Documented use

The dossier lists the following releases as having used Holophonics:

The dossier also states the system has been used in film soundtracks, popular music, television and theme parks, and that most famous sound effects were recorded in Modena at Umbi's Studios by sound engineer Maurizio Maggi.

The 1983 New Scientist exchange

Zuccarelli's article "Ears Hear by Making Sounds" appeared in New Scientist in 1983 (pp. 438–440). The dossier notes it was "soon followed by two letters, casting doubt on Zuccarelli's theory and his scientific abilities" — Baxter and Kemp, "Zuccarelli's Theory," New Scientist, 606 (1983).

Later uses of the term

The dossier also reproduces later patents that use "holophonic" or "holophone" in different senses. These are legal documents describing methods and devices; none is evidence that Zuccarelli's theory is correct.

• WO2014049268A1 (Corteel, Etienne et al.) — generating audio signals for a layered loudspeaker array, where at least one sound spatialisation technique is a holophonic technique.
• US9319794B2 (Betlehem, Terence) — a holophonic speaker system with filters pre-configured from measured acoustic transfer functions.
• DE102011011115A1 (Kirchhof, Axel) — a temporal-spatial crossed holophonic wave pattern formed by non-linear, chaotic initial conditions "corresponding to a neuronal pattern-building process."
• US6430293B1 (Finsterle, Luca Gubert) — a two-channel recording and playback system with a perspective corrector adjusting sound pressure from −15 dB to +9 dB with delayed emission to broaden the range to 360°.
• CN101325822A — a rotating dynamic recording/playback holography acoustic system in which playback rotates at the same speed and direction as recording.
• US3855578A (Watson, C. J. H.) — a "holophone" information storing and/or processing device using a collisionless plasma or spin-bearing material. This is a different sense of the term (plasma/spin-echo information processing) and should not be conflated with the audio system.

Limitations

The dossier contains no primary experimental data, no measurements, and no independent replication. It is a secondary/tertiary compilation mixing a Wikipedia article, patent abstracts, and library links. See Holophonics Claims vs. Evidence: The Interferometer Theory, the Demonstrations and the Binaural Explanation and Patent as Evidence.