Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Reexamination Certificate
1999-11-01
2003-04-08
Isen, Forester W. (Department: 2747)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
C381S001000
Reexamination Certificate
active
06546105
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a sound image localization device and a sound image localization method and, more particularly, to a construction for localizing a virtual sound image, in an arbitrary position, in AV (Audio, Visual) equipment.
BACKGROUND OF THE INVENTION
Recently, in the fields of movie and broadcasting, multi-channel audio signals (e.g., 5.1 channel) are recorded and reproduced by using digital audio compression techniques. However, such multi-channel audio signals cannot be reproduced by an ordinary television for domestic use because the audio output of the television for domestic use is usually two or less channels. Therefore, it is expected to realize the effect of multi-channel reproduction even in such AV equipment having two-channel audio reproduction function by using the technique of sound field control or the sound image control.
FIG. 2
is a block diagram illustrating the fundamental structure of a sound image localization apparatus (sound image reproduction apparatus) according to a prior art. Initially, description will be given of a method for localizing a sound image in a position on the forward-right to the front of a listener
9
by using speakers of output units
6
a
and
6
b
which are placed in front of the listener
9
. As shown in
FIG. 2
, the sound image localization apparatus includes a sound source
1
, signal processing means
5
a
and
5
b
, and output units
6
a
and
6
b.
The signal source
1
is signal input means for inputting a PCM (Pulse Code Modulated) audio signal S(t). A localization angle input unit
2
is an input unit for localization information of a virtual speaker
8
. A coefficient control unit
3
reads, from a coefficient memory
4
, filter coefficients for localizing the virtual speaker at an angle according to the information from the localization angle input unit
2
, and sets the filter coefficients in the signal processing means
5
a
and
5
b
. The signal processing means
5
a
is a digital filter having filter characteristics (transfer characteristics) hL(n) which are set by the coefficient control unit
3
, and the signal processing means
5
b
is a digital filter having filter characteristics (transfer characteristics) hR(n) which are set by the coefficient control unit
3
.
The output unit
6
a
converts the digital output supplied from the signal processing means
5
a
to an analog audio signal to be output. Likewise, the output unit
6
b
converts the digital output supplied from the signal processing means
5
b
to an analog audio signal to be output.
FIG. 3
is a block diagram illustrating the structure of the signal processing means
5
a
or
5
b
. The signal processing means
5
a
or
5
b
is an FIR (Finite Impulse Response) filter comprising n stages of delay elements (D)
13
a
~
13
n
, n+1 pieces of multipliers
14
a
~
14
(n+1), and an adder
15
. Input and output terminals of the respective delay elements
13
are connected with the respective multipliers
14
, and the outputs from the respective multipliers
14
are added by the adder
15
.
Now, the operation of the prior art sound image localization apparatus will be described with reference to
FIGS. 2 and 3
. In
FIG. 2
, a head-related transfer function between a speaker and an ear of the listener is called “impulse response”, and the value of an impulse response between the output unit
6
a
(speaker) and the left ear of the listener is given by h
1
(t). Hereinafter, impulse response is used when describing the operation in the time domain. Although the impulse response h
1
(t) is precisely the response in the position of the eardrum of the left ear of the listener when inputting an audio signal to the output unit
6
a
, measurement is performed in the position of the entrance of the external auditory miatus. The same result will be obtained even when considering the operation in the frequency domain.
Likewise, h
2
(t) is an impulse response between the output unit
6
a
and the right ear of the listener. Further, h
3
(t) is an impulse response between the output unit
6
b
and the left ear of the listener, and h
4
(t) is an impulse response between the output unit
6
b
and the right ear of the listener.
A virtual speaker
8
is a virtual sound source which is localized in a position on the forward-right to the front of the listener. Further, h
5
(t) is an impulse response between the virtual speaker
8
and the left ear of the listener, and h
6
(t) is an impulse response between the virtual speaker
8
and the right ear of the listener.
In the sound image localization apparatus so constructed, when the audio signal S(t) from the signal source
1
is output from the virtual speaker
8
, the sounds reaching the left and right ears of the listener
9
are represented by the following formulae (1) and (2), respectively.
left ear:
L
(
t
)=
S
(
t
)*
h
5
(
t
) (1)
right ear:
R
(
t
)=
S
(
t
)*
h
6
(
t
) (2)
wherein * represents convolutional arithmetic operation. Actually, these sounds are multiplied by the speaker's transfer function or the like, but it is ignored here to simplify the description. Alternatively, it may be assumed that the speaker's transfer function or the like is included in h
5
(t) and h
6
(t).
Further, the impulse responses and the signal S(t) are regarded as time-wise discrete digital signals, which are represented as follows.
L(t)→L(n)
R(t)→R(n)
h
5
(t)→h
5
(n)
h
6
(t)→h
6
(n)
S(t)→S(n)
wherein n represents integers. When T is the sampling time, n in ( ) should be nT, precisely. However, T is omitted here.
At this time, formulae (1) and (2) are represented as the following formulae (3) and (4), respectively, and the symbol * of convolutional operation is replaced with the multiplication symbol ×.
L
(
n
)=
S
(
n
)×
h
5
(
n
) (3)
R
(
n
)=
S
(
n
)×
h
6
(
n
) (4)
Likewise, when the signal S(t) is output from the output units
6
a
and
6
b
, the sound reaching the left ear of the listener is represented by the following formula (5).
L
′(
t
)=
S
(
t
)*
hL
(
t
)*
h
1
(
t
)+
S
(
t
)*
hR
(
t
)*
h
3
(
t
) (5)
When the signal S(t) is output from the output units
6
a
and
6
b
, the sound reaching the right ear of the listener is represented by the following formula (6.
R
′(
t
)=
S
(
t
)*
hL
(
t
)*
h
2
(
t
)+
S
(
t
)*
hR
(
t
)*
h
4
(
t
) (6)
When formulae (5) and (6) are represented by using (n) for the impulse responses, the following formulae (8) and (9) are obtained.
L
′(
n
)=
S
(
n
)×
hL
(
n
)×
h
1
(
n
)+
S
(
n
)×
hR
(
n
)×
h
3
(
n
) (8)
R
′(
n
)=
S
(
n
)×
hL
(
n
)×
h
2
(
n
)+
S
(
n
)×
hR
(
n
)×
h
4
(
n
) (9)
wherein hL(n) is the transfer characteristics of the signal processing means
5
a
, and hR(n) is the transfer characteristics of the signal processing means
5
b.
It is premised that, when the head-related transfer functions are equal, the listener hears the sounds from the same direction. This premise is generally correct. If the relationship of formula (10) is satisfied, formula (11) is established.
L
(
n
)=
L
(
n
) (10)
h
5
(
n
)=
hL
(
n
)×
h
1
(
n
)+
hR
(
n
)×
h
3
(
n
) (11)
Likewise, if the relationship of formula (12) is satisfied, formula (13) is established.
R
(
n
)=
R
′(
n
) (12)
h
6
(
n
)=
hL
(
n
)×
h
2
(
n
)+
hR
(
n
)×
h
4
(
n
) (13)
In order to make the listener hear a predetermined sound from the position of the virtual speaker
8
by using the output units
6
a
and
6
b
, the values of hL(n) and hR(n) are decided so as to satisfy formulae (11) and (13). For example, when formulae (11) and (13) are converted into the frequency-domain expression, the convolutional operation is replaced with multiplication and, thereafter, the respective impulse responses are subjected to FFT (Fas
Abe Kazutaka
Fujita Takeshi
Katayama Takashi
Kawamura Akihisa
Matsumoto Masaharu
Isen Forester W.
Matsushita Electric - Industrial Co., Ltd.
Pendleton Brian Tyrone
Wenderoth , Lind & Ponack, L.L.P.
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