Binaural synthesis, head-related transfer functions, and uses th

Details Binaural synthesis, head-related transfer functions, and uses th Binaural synthesis, head-related transfer functions, and uses th

1996-12-27

2000-09-12

Kuntz, Curtis A.

Electrical audio signal processing systems and devices

Binaural and stereophonic

381309, 381310, H04R 500

Patent

active

061188751

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to improved methods and apparatus for simulating the transmission of sound from sound sources to the ear canals of a listener, said sound sources being positioned arbitrarily in three dimensions in relation to the listener. In particular, the invention relates to novel uses of certain Head-related Transfer Functions and the production of such Head-related Transfer Functions, as well as to methods and apparatus using the Head-related Transfer Functions.


BACKGROUND OF THE INVENTION

Human beings detect and localize sound sources in three-dimensional space by means of the human binaural sound localization capability.
The input to the hearing consists of two signals: sound pressures at each of the eardrums. These two sound signals are called binaural sound signals. The term binaural refers to the fact that a set of two signals form the input to the hearing. It is not fully known how the hearing extracts information about distance and direction to a sound source, but it is known that the hearing uses a number of cues in this determination. Among the cues are coloration, interaural time differences, interaural phase differences and interaural level differences. Thorough descriptions of cues to directional hearing are given by J. Blauert: "Raumliches Horen", Hirzel Verlag, Stuttgart, Germany, 1974, and "Spatial Hearing", The MIT Press, Cambridge, Mass., 1983.
This means that if the sound pressures at the eardrums are created exactly as they would have been created by a given spatial sound field, a listener would not be able to distinguish this sound experience from the one he would get from being exposed to the spatial sound field itself.
One known way of approaching this ideal sound reproducing situation is by the artificial head recording technique. An artificial head is a model of a human head where the geometries of a human being which are acoustically relevant especially with respect to diffraction around the body, shoulder, head and ears are modelled as closely as possible. During a recording, e.g. of a concert, two microphones are positioned in the ear canals of the artificial head to sense sound pressures, and the electrical output signals from these microphones are recorded.
When these signals are reproduced, e.g. by headphones, the sound pressures in the ear canals of the artificial head during the concert are reproduced in the ear canals of the listener and the listener will achieve the perception that he was listening to the concert in the concert hall. The signals for the headphones are also called binaural signals.
The term binaural signals designates a set of two signals, left and right, having been coded using transmission characteristics corresponding to the transmission to the two ears of the human listener, for instance to be presented in the left and right ear canals, respectively, of a listener.
The binaural signals may typically be electrical signals, but they may also be, e.g. optical signals, electromagnetic signals or any other type of signal which can be transformed, directly or indirectly, into sound signals in the left and right ears of a human.
The transmission of a sound wave propagating from a sound source positioned at a give n direction and distance in relation to the left and right ears of the listener is described in terms of two transfer functions, one for the left ear and one for the right ear, that include any linear distortion, such as coloration, interaural time differences and interaural spectral differences. These transfer functions change with direction and distance of the sound source in relation to the ears of the listener. It is possible to measure the transfer functions for any direction and distance and simulate the transfer functions, e.g. electronically, e.g. by filters. If such filters are inserted in the signal path between a playback unit such as a tape recorder and headphones used by a listener, the listener will achieve the perception that the sounds generated by the headphones originate from a sound sou

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