Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Reexamination Certificate
1998-06-30
2001-09-04
Mei, Xu (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
C381S123000
Reexamination Certificate
active
06285766
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for localization of a sound image and, more particularly, to an apparatus for localization of a sound image which receives a sound signal, subjects the sound signal to signal processing, localizes a virtual sound image, and outputs a sound image localization signal.
BACKGROUND OF THE INVENTION
A conventional stereophonic system controls sound image localization using a plural of (generally two) loudspeakers, conferring a realistic sensation to the hearing of a listener. The conventional system usually includes two laterally spaced loudspeakers in front of the listener, so a sound image is localized between them. Outside the two loudspeakers no sound image is localized in the system. To obtain the effect that a sound image is localized outside the two loudspeakers, i.e., the surround of the listener, for instance, a sound from the back of the listener, the system sometimes includes loudspeakers at the rear as well as the two loudspeakers in front of the listener.
The development of technology for digitizing audio and hardware for DSP (Digital Signal Processor) facilitates various signal processing. Owing to this, the system using two loudspeakers in front of the listener can localize a sound image at any position around the listener, such as the side and rear of the listener.
Conventional sound image localization apparatus are disclosed in Japanese Patent Published Application Nos. Hei 3-270400 (1991); Hei 4-273800 (1992). A description will be given of a typical, conventional sound image localization apparatus.
FIGS.
19
(
a
) and
19
(
b
) are diagrams for explaining about sound image localization. FIG.
19
(
a
) shows a sound image to be localized in a virtual way. FIG.
19
(
b
) shows a system using two loudspeakers. In this case, it is assumed that the positions of virtually localized sound images, and the positions of the two loudspeakers are left-and-right symmetrical with respect to the listener.
In the sound image localization apparatus, a direction of a virtual position is localized and crosstalk is canceled by signal processing using a head related transfer function indicating transfer characteristics of sound from a sound source to the listener's head or ear.
Here, in case like FIG.
19
(
b
), a crosstalk signal is a signal transferred from a left loudspeaker to a right ear, or from a right loudspeaker to left ear. A signal is generated for canceling the crosstalk signal.
In the virtual environment achieved by this system as shown in FIG.
19
(
a
), sound signals uL and uR are radiated from the positions of virtual sound images located laterally at the back of the listener. Reference numerals, yL
1
and yR
1
, indicate sound pressures given to left and right ears, respectively. Because of the left-and-right symmetry, transfer of sound from the left virtual position to the left ear is the same as that from the right virtual position to the right ear. A head related transfer function showing this transfer characteristics is indicated by TM. The transfer of sound from the left virtual position to the right ear and that from the right virtual position to the left ear are represented by the same head related transfer function TC. The relation between the sound pressures and the functions are represented by
yL
1
=TM·uL+TC·uR (1-1) and
yR
1
=TC·uL+TM·uR (1-2).
On the other hand, in a system shown in FIG.
19
(
b
), left and right loudspeakers
1901
a
and
1901
b
radiate sound signals xL and xR, respectively. Sound pressures given to the left and right ears of the listener are yL
2
and yR
2
, respectively. As they are left-and-right symmetrical, the transfer of sound from the left loudspeaker position to the left car and that from the right loudspeaker position to the right ear are represented by the same head related transfer function SM. The transfer of sound from the left loudspeaker position to the right ear and that from the right loudspeaker position to the left ear are also represented by the same head related transfer function SC. The relation between those sound pressures and those functions are
yL
2
=SM·xL+SC·xR (2-1) and
yR
2
=SC·xL+SM·xR (2-2).
In this system, to localize the positions of the sound images shown in FIG.
19
(
a
) using acoustics output from the loudspeakers
1901
a
and
1901
b
, the following equations must be satisfied,
yL
1
=yL
2
(3-1) and
yR
1
=yR
2
(3-2).
The equations 3-1, 1-1, and 2-1 lead to the following equation 4-1, and the equations is 3-2, 1-2, and 2-2 lead to the following equation 4-2,
TM·uL+TC·uR=SM·xL+SC·xR (4-1) and
TC·uL+TM·uR=SC·xL+SM·xR (4-2).
The solution to xL and xR is obtained from the equations 4-1 and 4-2. If assumed that, the gain being represented by ═*═,
═(SC/SM)
2
═<<1 (5),
xL and xR are approximated by
xL~(FM+FC·FX)·uL+(FC+FM·FX)·uR (6-1) and
xR~(FC+FM·FX)·uL+(FM+FC·FX)·uR (6-2),
where FM=TM/SM (7-1),
FC=TC/SM (7-2), and
FX=−SC/SM (7-3).
Using the above relations, a conventional sound image localization apparatus is constructed, shown in FIG.
18
(
a
) . The conventional sound image localization apparatus comprises a crosstalk canceling means
1801
, direction localizing means
1802
a
and
1802
b
, and adders
1803
a
and
1803
b
. Sound signals are input through input terminals
1804
a
and
1804
b
. Signals resulting from subjecting the input sound signals to signal processing are output through output terminals
1805
a
and
1905
b.
The direction localizing means
1802
a
and
1802
b
process the sound signals input through the input terminals
1804
a
and
1804
b
to generate signals indicating the directions of sound image positions, respectively. The adders
1803
a
and
1803
b
add input signals. The crosstalk canceling means
1801
removes a crosstalk component of an input signal.
FIG.
18
(
b
) is a diagram illustrating a detailed structure of an example of the conventional sound image localization apparatus. The crosstalk canceling means
1801
shown in FIG.
18
(
a
) comprises crosstalk canceling signal generating filters
1806
a
and
1806
b
, and adders
1803
c
and
1803
d
. The direction localizing means
1802
a
and
1802
b
shown in FIG.
18
(
a
) comprise main-path filters
1807
a
and
1807
b
, and crosstalk-path filters
1808
a
and
1808
b
, respectively. The combination of the main-path filter and the crosstalk-path filter is sometimes called a direction localizing filter.
The prior art sound image localization apparatus generates the outputs xL and xR according to the expressions 6-1 and 6-2. A description will be given of how the sound image localization apparatus works.
Left and right input sound signals are input through the input terminals
1804
a
and
1804
b
, respectively. The first input sound signal input through the input terminal
1804
a
is input to the main-path filter
1807
a
and the crosstalk-path filter
1808
a
. The main-path filter
1807
a
multiplies the input signal by the coefficient shown in the equation 7-1. The crosstalk-path filter
1808
a
multiplies the input signal by the coefficient shown in the equation 7-2. The outputs of the main-path filter
1807
a
and the crosstalk-path filter
1808
a
are input to the adders
1803
a
and
1803
b
, respectively.
Similarly, the second input sound signal input through the input terminal
1804
b
is input to the main-path filter
1807
b
and the crosstalk-path filter
1808
b
, where the input signal is multiplied by the coefficients expressed by 7-1 and 7-2, respectively. The outputs of the main-path filter
1807
b
and the crosstalk-path filter
1808
b
are input to the adders
1803
b
and
1803
a
, respectively.
The adders
1803
a
and
1803
b
each add input signals. The adder
1803
a
outputs a result of the addition to the adder
1803
c
and the crosstalk canceling signal generating filter
1806
a
. The crosstalk canceling signal gener
Matsushita Electric - Industrial Co., Ltd.
Mei Xu
Parkhurst & Wendel L.L.P.
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