Sound signal refining method, sound signal decoding method, apparatus thereof, program, and storage medium
A sound signal purification method includes an n-th channel signal purification step of obtaining, for each frame and for each corresponding sample t with respect to each channel n, a sequence based on a value ˜ x n (t)=(1−α n )×{circumflex over ( )}x n (t)+α n ×{circumflex over ( )}x M (t) obtained by adding a value α n ×{circumflex over ( )}x M (t) obtained by multiplying an n-th channel purification weight α n by a sample value {circumflex over ( )}x M (t) of the monaural decoded sound signal {circumflex over ( )}X M and a value (1−α n )×{circumflex over ( )}x n (t) obtained by multiplying a value (1−α n ) obtained by subtracting the n-th channel purification weight α n from 1 by a sample value {circumflex over ( )}x n (t) of the n-th channel decoded sound signal {circumflex over ( )}X n , as the n-th channel purified decoded sound signal ˜ X n .
1 . A sound signal purification method, comprising:
obtaining, for each frame, an n-th channel purified decoded sound signal ˜ X n by using at least an n-th channel decoded sound signal {circumflex over ( )}X n (n is each integer of 1 or more and N or less) and a monaural decoded sound signal {circumflex over ( )}X M , wherein
the n-th channel purified decoded sound signal ˜ X n represents a sound signal of each channel of stereo,
the n-th channel decoded sound signal {circumflex over ( )}X n represents a decoded sound signal of said each channel of stereo obtained by decoding a stereo code CS,
the monaural decoded sound signal {circumflex over ( )}X M represents a monaural decoded sound signal obtained by decoding a monaural code CM,
the monaural code CM is distinct from the stereo code CS,
the n-th channel decoded sound signal {circumflex over ( )}X n is obtained by decoding the stereo code CS using aspects of the stereo code CS and without using either information obtained by decoding the monaural code CM or the monaural code CM, and
the obtaining the n-th channel purified decoded sound signal ˜ X n further comprises obtaining, for the each frame and for each corresponding sample t with respect to the each channel n, the n-th channel purified decoded sound signal ˜ X n as a sequence based on a value ˜x n (t)=(1−α n )×{circumflex over ( )}x n (t)+α n ×{circumflex over ( )}x M (t), the value ˜ x n (t) is obtained by adding a value α n ×{circumflex over ( )}x M (t) and a value (1−α n )×{circumflex over ( )}x n (t), the value α n ×{circumflex over ( )}x M (t) is obtained by multiplying an n-th channel purification weight α n by a sample value {circumflex over ( )}x M (t) of the monaural decoded sound signal {circumflex over ( )}X M , the value (1−α n )×{circumflex over ( )}x n (t) is obtained by multiplying a value (1−α n ) and a sample value {circumflex over ( )}x n (t) of the n-th channel decoded sound signal {circumflex over ( )}X n , and the value (1−α n ) is obtained by subtracting the n-th channel purification weight α n from 1.
2 . The sound signal purification method according to claim 1 , further comprising
obtaining,
for the each frame with respect to the each channel n,
the n-th channel purification weight α n by
α
n
=
2
-
2
b
n
T
2
-
2
b
n
T
+
2
-
2
b
M
T
using a number of samples T per frame, a number of bits b n corresponding to an n-th channel in a number of bits of the stereo code CS, and a number of bits b M of the monaural code CM.
3 . The sound signal purification method according to claim 1 , further comprising
obtaining,
for the each frame with respect to the each channel n,
the n-th channel purification weight α n is according to a value in a range that is greater than 0 and less than 1,
the n-th channel purification weight α n is has a value 0.5 when a number of bits b n corresponding to an n-th channel in a number of bits of the stereo code CS and a number of bits b M of the monaural code CM are equal,
the n-th channel purification weight α n is has a value approaching 0 from 0.5 as the b n is greater than the b M , and
the n-th channel purification weight α n is has a value approaching 1 from 0.5 as the b M is greater than the b n .
4 . The sound signal purification method according to claim 1 , further comprising
obtaining,
for the each frame with respect to the each channel n,
a value c n ×r n as the n-th channel purification weight α n by multiplying
a normalized inner product value r n for the monaural decoded sound signal {circumflex over ( )}X M of the n-th channel decoded sound signal {circumflex over ( )}X n by
a correction coefficient c n obtained by
c
n
=
2
-
2
b
n
T
2
-
2
b
n
T
+
2
-
2
b
M
T
using a number of samples T per frame, a number of bits b n corresponding to an n-th channel in a number of bits of the stereo code CS, and a number of bits b M of the monaural code CM.
5 . The sound signal purification method according to claim 4 , wherein
the n-th channel purification weight α n indicates a value λ×c n ×r n , wherein the value λ×c n ×r n is obtained by multiplying the normalized inner product value r n , the correction coefficient c n , and a predetermined value λ, and the predetermined value λ is larger than 0 and smaller than 1 as the n-th channel purification weight α n .
6 . The sound signal purification method according to claim 4 , wherein
a number N of channels comprising the each channel n is two, and
the n-th channel purification weight α n further comprises obtaining
the n-th channel purification weight α n corresponding to a value γ×c n ×r n , wherein the value is γ×c n ×r n obtained by multiplying the normalized inner product value r n , the correction coefficient c n , and an inter-channel correlation coefficient γ, and the inter-channel correlation coefficient γ indicates a correlation coefficient between a first channel decoded sound signal and a second channel decoded sound signal.
7 . The sound signal purification method according to claim 1 , further comprising:
obtaining,
for the each frame with respect to the each channel n,
with a number of bits corresponding to an n-th channel in a number of bits of the stereo code CS as b n and a number of bits of the monaural code CM as b M ,
the n-th channel purification weight α n according to a value c n ×r n by multiplying a correction coefficient c n and a value r n ,
the value r n approaches 1 as a correlation of waveforms between the n-th channel decoded sound signal {circumflex over ( )}X n and the monaural decoded sound signal {circumflex over ( )}X M increases and approaches 0 as the correlation of waveforms decreases,
the correction coefficient c n represents a value in a range that is greater than 0 and less than 1,
the correction coefficient c n has a value of 0.5 when the b n and the b M are same,
the correction coefficient c n has a value that approaches 0 from 0.5 as the b n is larger than the b M , and
the correction coefficient c n has a value that approaches 1 from 0.5 as the b n is smaller than the b M .
8 . The sound signal purification method according to claim 1 , wherein
T is a number of samples per frame and each of ε n and ε M is a value larger than 0 and smaller than 1, and
the sound signal purification method further comprises
obtaining,
for the each frame with respect to the each channel n,
a value c n ×r n obtained by multiplying
a normalized inner product value r n obtained by
r n =E n (0)/ E M (0)
using an inner product value E n (0) obtained by
E
n
(
0
)
=
ϵ
n
E
n
(
-
1
)
+
(
1
-
ϵ
n
)
T
∑
t
=
1
T
x
^
n
(
t
)
x
^
M
(
t
)
using each sample value {circumflex over ( )}x n (t) of the n-th channel decoded sound signal {circumflex over ( )}X n , each sample value {circumflex over ( )}x M (t) of the monaural decoded sound signal {circumflex over ( )}X M , and an inner product value E n (−1) of a previous frame, and
energy E m (0) of the monaural decoded sound signal obtained by
E
M
(
0
)
=
ϵ
M
E
M
(
-
1
)
+
(
1
-
ϵ
M
)
T
∑
t
=
1
T
x
^
M
(
t
)
x
^
M
(
t
)
using the each sample value {circumflex over ( )}x M (t) of the monaural decoded sound signal {circumflex over ( )}X M and energy E M (−1) of the monaural decoded sound signal of the previous frame, by
a correction coefficient c n obtained by
c
n
=
2
-
2
b
n
T
2
-
2
b
n
T
+
2
-
2
b
M
T
using a number of samples T per frame, a number of bits b n corresponding to an n-th channel in a number of bits of the stereo code CS, and a number of bits b M of the monaural code CM, as the n-th channel purification weight α n .
9 . A sound signal decoding method comprising the sound signal purification method according to claim 1 as a sound signal purification step, the sound signal decoding method further comprising:
a stereo decoding step of decoding the stereo code CS to obtain the n-th channel decoded sound signal {circumflex over ( )}X n of the each channel n without using either information obtained by decoding the monaural code CM or the monaural code CM; and
a monaural decoding step of decoding the monaural code CM to obtain the monaural decoded sound signal {circumflex over ( )}X M .
10 . A non-transitory recording medium recording a program for causing a computer to execute the sound signal purification method according to claim 1 .
11 . A sound signal purification device comprising:
a memory; and
a processor executing a computer-executable program instruction that cause the sound signal purification device to perform:
obtaining, for each frame, an n-th channel purified decoded sound signal ˜ X n by using at least an n-th channel decoded sound signal {circumflex over ( )}X n (n is each integer of 1 or more and N or less) and a monaural decoded sound signal {circumflex over ( )}X M , wherein
the n-th channel purified decoded sound signal ˜ X n represents a sound signal of each channel of stereo,
the n-th channel decoded sound signal {circumflex over ( )}X n represents a decoded sound signal of the each channel of stereo obtained by decoding a stereo code CS,
the monaural decoded sound signal {circumflex over ( )}X M represents a monaural decoded sound signal obtained by decoding a monaural code CM,
the monaural code CM is distinct from the stereo code CS,
the n-th channel decoded sound signal {circumflex over ( )}X n is obtained by decoding the stereo code CS using aspects of the stereo code CS and without using either information obtained by decoding the monaural code CM or the monaural code CM, and
the obtaining the n-th channel purified decoded sound signal ˜ X n further comprises obtaining, for the each frame and for each corresponding sample t with respect to the each channel n, the n-th channel purified decoded sound signal ˜ X n as a sequence based on a value ˜ x n (t)=(1−α n )×{circumflex over ( )}x n (t)+α n ×{circumflex over ( )}x M (t), the value ˜ x n (t) is obtained by adding a value α n ×{circumflex over ( )}x M (t) and a value (1−α n )×{circumflex over ( )}x n (t), the value α n ×{circumflex over ( )}x M (t) is obtained by multiplying an n-th channel purification weight α n by a sample value {circumflex over ( )}x M (t) of the monaural decoded sound signal {circumflex over ( )}X M , the value (1−α n )×{circumflex over ( )}x n (t) is obtained by multiplying a value (1−α n ) and a value {circumflex over ( )}x n (t) of the n-th channel decoded sound signal {circumflex over ( )}X n , and the value (1−α n ) is obtained by subtracting the n-th channel purification weight α n from 1.
12 . A sound signal decoding device comprising the sound signal purification device according to claim 11 as a sound signal purification circuitry, the sound signal decoding device further comprising:
a stereo decoding circuitry configured to decode the stereo code CS to obtain the n-th channel decoded sound signal {circumflex over ( )}X n of the each channel n without using either information obtained by decoding the monaural code CM or the monaural code CM; and
a monaural decoding circuitry configured to decode the monaural code CM to obtain the monaural decoded sound signal {circumflex over ( )}X M .