Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Patent
1997-05-27
1999-11-09
Isen, Forester W.
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
381303, 381 26, 381 17, H04R 500
Patent
active
059829036
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of building an acoustic transfer function table for virtual sound localization control, a memory with the table stored therein, and an acoustic signal editing scheme using the table.
There have been widespread CDs that delight the listeners with music of good sound quality. In the case of providing music, speech,sound environment and other audio services from recording media or over networks, it is conventional to subject the sound source to volume adjustment, mixing, reverberation and similar acoustic processing prior to reproduction of the virtual sound through headphones or loudspeaker. A technique for controlling sound localization can be used for such processing to enhance an acoustic effect. This technique can be used to make a listener perceive sounds at places where no actual sound sources exist. For example, even when a listener listens to sounds through headphones (binaural listening), it is possible to make her or him perceive the sounds as if a conversation was being carried out just behind him. It is also possible to simulate sounds of vehicles as if they were passing through in front of the listener.
Also in an acoustical environment of virtual reality or cyber space, the technique for virtual sound localization can be applicable. A familiar example of the application is the production of a sound effect in video games. Usually acoustic signals processed for sound localization are provided to a user by reproducing them from a semiconductor ROM, CD, MD, MT or similar memory; alternatively, acoustic signals are provided to the user while being processed for sound localization on a real time basis.
What is intended by the term "sound localization" is that a listener judges the position of a sound she or he is listening to. Usually the position of the sound source agrees with the judged position. Even in the case of reproducing sounds through headphones (binaural listening), however, it is possible to make the listener perceive sounds as if they are generated from desired target positions. The principle of sound localization is to replicate or simulate in close proximity to the listener's eardrums sound stimuli from each sound source placed at each of the desired target positions. Convolution of the acoustic signal of the sound source with coefficients characterizing sound propagation from the target position to the listener's ears such as acoustic transfer functions, is proposed as a solution of the implementation. The method will be described below.
FIG. 1A illustrates an example of sound reproduction by using a single loudspeaker 11. Let an acoustic signal to the loudspeaker 11 and acoustic transfer functions from the loudspeaker 11 to the eardrums of left and right ears 13L and 13R of a listener 12 (which are referred to as head related transfer functions) be represented by x(t), h.sub.l (t) and h.sub.r (t), as functions of time t respectively. The acoustic stimuli in the close proximity to the left and right eardrums are as follows: (t) and h.sub.r (t) are represented by impulse responses that are functions of time. In the actual digital acoustic signal processing, they are each provided as a coefficient sequence composed of a predetermined number of coefficients spaced a sampling period apart.
FIG. 1B illustrates sound reproduction to each of the left and right ears 13L and 13R through headphones 15 (binaural listening). In this case, the acoustic transfer functions from the headphones 15 to the left and right eardrums (hereinafter referred to as ear canal transfer functions) are given by e.sub.l (t) and e.sub.r (t), respectively. Prior to sound reproduction, the acoustic signal x(t) is convolved by using left and right convolution parts 16L and 16R with coefficient sequences s.sub.l (t) and s.sub.r (t), respectively. At this time, acoustic stimuli at the left and right eardrums are as follows: as follows: and (2a) and that between Eqs. 1(b) and (2b), respectively, the acoustic stimuli generated from the sound source 11 in FIG. 1A ar
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Aoki Shigeaki
Kinoshita Ikuichiro
Isen Forester W.
Mei Xu
Nippon Telegraph and Telephone Corporation
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