Electrical audio signal processing systems and devices – Binaural and stereophonic – Stereo sound pickup device
Patent
1996-03-20
1997-09-09
Oh, Minsun
Electrical audio signal processing systems and devices
Binaural and stereophonic
Stereo sound pickup device
381 1, 381 24, H04R 500
Patent
active
056664257
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a plural-channel sound processing system and has particular, although not exclusive, relevance to such systems as may be used to record music for playback via two loudspeakers.
The principles of sound recording such that, on playback via two spaced sound sources, a stereophonic effect is perceived have long been known. One of the commonest forms of stereophonic sound recording involves using a stereo microphone pair, with the microphones spaced-apart by a distance approximately equal to one head width. This produces an effect of being able to partially reproduce the acoustic image recorded owing to the different arrival times of various sounds between the microphone pair, owing to their separation.
The above technique is far from satisfactory, however, and attempted improvements in stereo recording often utilised a so-called artificial head. This is an artificial lifesize head (and optionally) torso in which a pair of microphones are mounted either in substitution of the ear canals, or incorporated into simulated ear canals. The external ear parts are reproduced according to mean human dimensions and are manufactured from silicone rubber or similar material such that the sounds which the microphones record have been acoustically modified by the artificial head and ears so as to possess all of the natural sound localisation cues used by the brain. Such recording techniques have become known as binaural recordings and an example of one such technique is disclosed in, for example, U.S. Pat. No. 4,910,779.
Such artificial head recording techniques are known to possess remarkable acoustical properties when listened to via headphones. Sounds may be perceived as emanating from outside the listener's head, rather than inside it as with conventional stereophonic recordings which are listened to via headphones, and may also be perceived in three dimensions--even above and behind the listener's head.
There also exist many problems associated with artificial head recordings. For example, it is known that the tonal qualities of binaural recordings are not true to life. This is due to the fact that sounds pass, effectively, through two sets of ears; those of the artificial head during recording, and those of the listener during playback. There is generally a resonance associated with the main cavity in the external ear (the coneha) which occurs at a frequency of several kHz and boosts the mid-range gain of the recording and hence as a consequence of passing through the second set of ears during playback this effect is exacerbated and the sounds appear to lack both low-frequency and high-frequency content.
In order to compensate for this "twice-through-the-ears" effect it is known to use audio filters to shape, or equalise, the spectral response of the sound recorded via the artificial head. The transfer function used for this shaping has been calculated in the prior art in many different ways and confusion seems to exist over which way is the best way to equalise the artificial head recordings. Some practitioners use headphone-to-ear transfer functions, yet these functions will differ from one headphone type to another. Some practitioners use loudspeaker-to-ear transfer functions--here the functions are dependent both upon the angle of incidence of the sound from the loudspeaker to the ear and the distance from the head to the loudspeaker. Other practitioners measure transfer functions under both free-field (anechoic) and diffuse-field (echoic) conditions and then compensate according to either the headphone-to-ear or loudspeaker-to-ear requirements.
When playback of a binaurally recorded sound via loudspeakers occurs, it is known that a further important correction factor is needed. This is known as transaural crosstalk compensation and is also described in the acknowledged prior art. This correction factor essentially compensates for sound detected by the left ear originating from a loudspeaker nearer to the right ear and vice versa. An example of this well-known technique is disclosed
REFERENCES:
patent: 3236949 (1966-02-01), Atal et al.
patent: 4096353 (1978-06-01), Bauer
patent: 4910779 (1990-03-01), Cooper et al.
patent: 5034983 (1991-07-01), Cooper et al.
patent: 5173944 (1992-12-01), Begault
Clemow Richard David
Nackvi Fawad
Philp Adam
Sandford Adrian Miles
Sibbald Alastair
Central Research Laboratories Limited
Oh Minsun
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