Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Ear or nose prosthesis
Reexamination Certificate
2000-01-13
2002-06-11
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Ear or nose prosthesis
Reexamination Certificate
active
06402782
ABSTRACT:
The present invention relates to a novel artificial ear and auditory canal system, and a means of manufacture of the same.
The invention has particular application in the field of binaural, three-dimensional sound recording and associated techniques, and also in the fields of noise measurement and hearing prostheses development.
Artificial head recording systems are now well known (see for example U.S. Pat. No. 1,855,149) A typical artificial head system comprises a pair of microphones mounted on to the sides of an artificial head assembly where the auditory canal would be, inset into a pair of artificial pinnae (the visible ear flaps). A recording made with an artificial head incorporates many of the 3D sound “cues” which our brains use to interpret the positions of sound sources in 3D space, and so such recordings provide quite dramatic 3D effects when auditioned over headphones. More recently, it has become possible to make acoustic measurements on artificial heads (the measurement of Head-Response Transfer Functions—HRTFs), and synthesise the effects of the head and ears electronically, using digital signal-processing. However, although these effects are initially perceived to be quite dramatic, especially when heard for the first time, several major deficiencies in present-day artificial heads become apparent when they are tested more rigorously.
The two prime deficiencies are (a) poor “height” effects, and (b) poor front-back discrimination. For example, in respect of (a), this means that when a recording is made of a sound-source moving over the top of the head (from, say, a position close to the left ear, over the head to a position close to the right ear), then the sound-source appears to move directly through the head, rather than over the top. In respect of (b), if a recording were made of a sound-source moving around the artificial head in the horizontal plane in a circle of constant distance (say 1 meter), then the recorded source would appear to move back and forth in arcs from the left ear to the right, always in front of the listener and never behind. These spatial inaccuracies are often overlooked or ignored for recording purposes, where most real-life sound-sources are in front of the artificial-head/listener, and not in these more extreme positions. Nevertheless, the poor spatial accuracy of presently available artificial heads prevents the synthesis of an adequate 360° sound-field, such as is required for computer games applications, immersive virtual reality, simulators and the like.
Many researchers have been puzzled over why their artificial head systems are inadequate in the above respects. Some have turned to making measurement on real head-ear systems, by embedding miniature microphones in the pinnae or auditory canals of experimental volunteers. Others have resorted to building their own artificial head systems, attempting to improve on the products of commercial manufacturers, and, in some cases, have taken molding from the ears of volunteers for replicating and using. In one extreme example, U.S. Pat. No. 4,680,856 (Zuccarelli) attempted to replicate or simulate the entire anatomy of the skull, including the bones, double-twisted oval auditory canals, Eustachian tubes, teeth and skin, in order to copy reality as closely as possible. Zuccarelli even stated that a wig was necessary in order to provide good front-back discrimination! Clearly, this latter approach is totally unsuitable for a manufactured product in terms of expense and operational factors (weight, bulk and appearance). In addition, this approach does not allow for the creation of a system with adequate Left-Right matching, because very small L-R differences, introduced during manufacture, in the size, shape or position of any of the acoustic cavities in the structure create significant differences in the overall properties and HRTFs.
The first demonstration of a stereophonic effect is believed to have taken place in Paris in the 1890s, when multiple microphones situated in an array across the front of a stage were each connected to individual ear pieces in an adjacent room, and listeners found that the use of adjacent pairs of ear pieces (and hence microphones) provided very realistic sound reproduction with spatial properties. The first explicit report of a dummy-head type of sound reproduction method appears in U.S. Pat. No. 1,855,149, dated 1927 in which the purpose was to record sounds in such a way that the natural, head-related time-of-arrival and amplitude differences between L and R signals were convolved acoustically on to the sounds, and then replay was achieved using either earphone reproducers or equidistant loudspeakers, placed directly to the left and right of the listener, such that “the virtual sound origins were secured”. British Patent No.394325 (Blumlein) filed in 1931 relates to conventional, present-day stereo in which the use of two or more microphones and appropriate elements in the transmission circuit were used to provide directional-dependent loudness of the loudspeakers, together with means to cut discs and thus record the signals. Stereo sound recording and reproduction was not commercially exploited widely until the 1950s.
At the present time, conventional stereo is largely Blumlein's amplitude-based stereo, in which a number of individual, monophonic recordings are effectively “placed” spatially in the sound-stage between the listener's loudspeakers by virtue of their L-R loudness differences. This is achieved by “pan-potting”. It is possible to add artificial reverberation and other effects to enhance the spatial aspects (room acoustics, and distance) of these recordings.
When live recordings are being made, it is common to use stereo microphone pairs, placed so as to be either (a) coincident, or (b) spaced-apart by about one head-width, or thereabouts. This latter goes part-way to the reproduction of a natural acoustic image of a performance, but there have been several periods since the 1950s when the use of the dummy-head recording method for producing binaural signals has been experimented with for improving the quality of the stereo image.
Historically, the term “stereophonic” was coined in the 1950s to apply to sound reproduction over two or more transmission channels. In the 1970s, there was a resurgence of interest in recording using dummy-head microphone techniques, and the expression “binaural” was coined exclusively for recordings made by such means. More recently, the term “binaural” has also been used for electronic equivalents, where the acoustic processing effects of the human head and external ear are synthesised.
Dummy-head (binaural) recording systems comprise an artificial, life-size head and sometimes torso, in which a pair of high-quality microphones are mounted in the ear auditory canal positions. The external ear parts are reproduced according to mean human dimensions, and manufactured from silicon rubber or similar material, such that the sounds which the microphones record have been modified acoustically by the dummy head and ears so as to possess all of the natural sound localisation cues used by the brain.
Following on from the development of somewhat crude and simple artificial heads for binaural sound recording in the 1930s and 1940s, acousticians became aware that these head structures were ideal platforms for testing and evaluating hearing aids and other devices, such as hearing defenders (ear-plugs). Consequently, a more academic interest was taken in the development of artificial heads, with more care taken in their construction and engineering. For example, the papers by Torick (An electronic dummy for accoustical testing E. L. Torick et al., J. Audio Eng. Soc., October 1988, 16, (4), pp. 397-402) and Burkhardt and Sachs (Anthropometric manikin for acoustic research M D Burkhardt and R M Sachs, J. Acoust. Soc. Am., July 1975, 58, (1), pp. 214-222) are two excellent papers to study for more information about artificial heads. It soon became clear that, although the simple, earliest head structures were adeq
Sibbald Alastair
Warner George Derek
Warner Johanna
Bollman William H.
Central Research Laboratories Limited
McDermott Corrine
Phan Hieu
Warner Johanna
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