Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Reexamination Certificate
1999-01-22
2003-01-07
Lee, Ping (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
C381S001000
Reexamination Certificate
active
06504934
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for localizing sound image.
2. Description of the Related Art
Conventionally, a home television (TV) set capable of performing a stereophonic audio reproduction includes a pair of speakers (i.e., a left speaker and a right speaker). However, since such a TV set has a limited width for installing the speakers therein, it is not possible to enjoy stereophonic audio reproduction at satisfactory level. Furthermore, if such a TV set employs a “surround system”, it is often difficult to provide surround speakers.
In such a case, audio signals are subjected to a localization treatment of sound image (e.g., by using a head-related transfer function (HRTF)) and the treated signals are supplied to the speakers, so as to localize sound image (i.e., virtual speakers) at positions where speakers are not actually arranged. The virtual speakers make a listener to feel that the distance between the actually arranged speakers is widen, or to feel that the listener hears reproduced sound from sideward or rearward of the listener although only two frontal speakers are actually arranged in front of the listener.
Generally, in the case of moving sound image, it is relatively easy to localize the sound image at a predetermined position although it depends on a listener. In contrast, in the case of staying sound image, it is difficult to localize the sound image at a predetermined position.
In order to overcome the above-mentioned problem, a technique making a listener to recognize sound image at a predetermined position has been proposed. When the predetermined position is located away at an angle &thgr; in a circumferential direction from the front of the listener, the technique includes producing (i) a first processed signal for localizing sound image at a first localization position located away at an angle &thgr;
1
in a circumferential direction from the front of the listener wherein &thgr;
1
<&thgr;, and (ii) a second processed signal for localizing sound image at a second localization position located away at an angle &thgr;
2
in a circumferential direction from the front of the listener wherein &thgr;
2
>&thgr;; and alternately supplying the first and the second processed signals to the speakers, so as to alternately localize sound image at the first and the second localization position for making the listener to recognize sound image at the predetermined position.
However, such a technique provides the listener with a quite unnatural feeling of hearing due to the regularity of the alternate sound image localization around the predetermined position.
Next, the case of moving sound image will be described.
An apparatus, wherein a pair of speakers are arranged at positions left and right front sides of a listener and wherein a single audio signal is divided into two branched signals to be supplied to the respective speakers, is capable of moving sound image in a left or right direction between the speakers. The sound image movement is accomplished by, for example, continuously increasing an amplitude (a level) of one of the branched signals as well as continuously decreasing an amplitude of another branched signal.
However, in the case of simply increasing and decreasing the amplitude of the branched signals, a listener often feels that the sound image is moving in an area rearwards to the speakers when the sound image is located at the middle between the speakers. In order to make the listener to feel that the sound image is moving in a left or right direction between the speakers, the following procedure is conventionally employed.
(i) When sound image is located at the middle between the left and right speakers, the procedure includes increasing an amplitude of the branched signals in a small amount, respectively. (ii) When sound image is moving from left or right side to the middle between the speakers, the procedure includes shifting a frequency component to high frequency side in advance, and then returning the shifted component to an original one as sound image is moving to the middle between the speakers. In contrast, when sound image is moving from the middle between the speakers to left or right side, the procedure includes shifting a frequency component to low frequency side in advance, and then returning the shifted component to an original one as sound image is moving to left or right side. In other words, the procedure includes incorporating the Doppler effect. Alternatively, (iii) when sound image is moving from left or right side to the middle between the speakers, the procedure includes virtually increasing a high frequency component of the branched signals and decreasing a low frequency component thereof. In contrast, when sound image is moving from the middle between the speakers to left or right side, the procedure includes virtually increasing a low frequency component of the branched signals and decreasing a high frequency component thereof.
As described above, it is relatively easy to make a listener to feel that sound image is moving in a left or right direction. However, it is difficult to make a listener to feel that sound image is moving forward and backward with respect to the listener by using only two speakers (i.e., the left and right speakers).
For example, when sound image is approaching a listener, it is possible to make the listener to feel that the sound image is approaching the listener to some extent, by gradually increasing an amplitude of the branched signals. Especially, when a picture image is accompanied with the sound image, such a feeling may be emphasized. However, it is not possible to make a listener to feel that sound image is approaching the listener sufficiently or moving rearwards with respect to the listener.
In order to overcome the above-mentioned problem, the below-indicated technique has been proposed. As shown in
FIG. 26
, when branched signals supplied to a left speaker
211
and a right speaker
212
have the same phase (i.e., the correlation is 1), a listener
214
feels that sound image
213
is located at the position
220
rearwards of the middle between the speakers
211
and
212
; when the phase difference between the branched signals is 90 degrees (i.e., the correlation is zero), a listener
214
feels that sound image
213
is widen in an area
221
between the speakers
211
and
212
; when the phase difference between the branched signals is 180 degrees (i.e., the correlation is −1), a listener
214
feels that sound image
213
is located at an area
222
rearwards to the listener
214
. The technique includes moving sound image
213
forward and backward with respect to the listener by varying the phase difference between the branched signals (i.e., by using a relationship shown in FIG.
26
).
However, even when the above-mentioned technique is utilized, it is not possible to make a listener
214
to clearly feel that sound image
213
is moving forward and backward with respect to the listener.
As described above, an apparatus and a method for localizing sound image which provide a natural feeling of hearing is eagerly demanded.
SUMMARY OF THE INVENTION
The present invention includes the steps of providing a left speaker and a right speaker in front of a listener; subjecting an audio signal to a sound image localization treatment, so as to produce a processed signal; and supplying the processed signal to the left and the right speakers, so as to localize sound image at a predetermined position. Wherein the method further includes: producing a first processed signal which localizes sound image at a first localization position and a second processed signal which localizes sound image at a second localization position; multiplying one of the first and the second processed signals by a coefficient k which varies in the range of 0 to 1; multiplying the other signal by a coefficient 1−k; and adding the processed signal multiplied by the coefficient k and the processed signal multiplied by the c
Kasai Joji
Nakatake Tetsuro
Sadaie Koichi
Takemura Kazumasa
Toyofuku Kenichiro
Bednarek Michael D.
Lee Ping
Onkyo Corporation
Shaw Pittman LLP
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