Sound signal purification using decoded monaural signals
View Patent ↗A sound signal purification method includes a monaural decoded sound upmixing step of obtaining, an n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn that is a signal obtained by upmixing a monaural decoded sound signal {circumflex over ( )}X M for each channel by an upmixing process using the monaural decoded sound signal {circumflex over ( )}X M and inter-channel relationship information that is information indicating a relationship between channels of stereo, and an n-th channel signal purification step of obtaining a sequence based on a value {tilde over ( )}x n (t) obtained by adding a value α n ×{circumflex over ( )}x Mn (t) obtained by multiplying an n-th channel purification weight α n by a sample value {circumflex over ( )}x Mn (t) of the n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn and a value 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 .
1. A sound signal purification method for obtaining, for each frame, an n-th channel purified decoded sound signal {circumflex over ( )}X n that is a sound signal of each channel of stereo 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) that is a decoded sound signal of the each channel of the stereo obtained by decoding a stereo code CS and a monaural decoded sound signal {circumflex over ( )}X M that is a monaural decoded sound signal obtained by decoding a monaural code CM that is a code different from the stereo code CS, wherein
the n-th channel decoded sound signal {circumflex over ( )}X n is obtained by decoding the stereo code CS without using either information obtained by decoding the monaural code CM or the monaural code CM, and
the sound signal purification method further comprises
a monaural decoded sound upmixing step of obtaining, for the each frame, an n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn that is a signal obtained by upmixing the monaural decoded sound signal {circumflex over ( )}X M for the each channel by an upmixing process using the monaural decoded sound signal {circumflex over ( )}X M and inter-channel relationship information that is information indicating a relationship between the channels of the stereo, and
an n-th channel signal purification step of obtaining, for the each frame and for each corresponding sample t with respect to the each channel n, a sequence based on a value {circumflex over ( )}x n (t)=(1−a n )×{circumflex over ( )}x n (t)+α n ×{circumflex over ( )}X Mn (t) obtained by adding a value α n ×{circumflex over ( )}X Mn (t) obtained by multiplying an n-th channel purification weight α n by a sample value {circumflex over ( )}x Mn (t) of the n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn and a value (1−a n )× {circumflex over ( )}X n (t) obtained by multiplying a value (1−a 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 {circumflex over ( )}X n .
2. The sound signal purification method according to claim 1 , wherein
a number N of the channels is two,
the inter-channel relationship information includes information indicating a number of samples |τ| corresponding to a time difference between channels of a first channel and a second channel and information indicating which of the first channel and the second channel is preceding, and
the monaural decoded sound upmixing step
obtains the monaural decoded sound signal without change as the first channel upmixed monaural decoded sound signal {circumflex over ( )}X M1 and obtains a signal obtained by delaying the monaural decoded sound signal by |τ| samples as the second channel upmixed monaural decoded sound signal {circumflex over ( )}X M2 in a case where the first channel is preceding, and
obtains a signal obtained by delaying the monaural decoded sound signal by |τ| samples as the first channel upmixed monaural decoded sound signal {circumflex over ( )}X M1 and obtains the monaural decoded sound signal without change as the second channel upmixed monaural decoded sound signal {circumflex over ( )}X M2 in a case where the second channel is preceding.
3. The sound signal purification method according to claim 1 , further comprising
an n-th channel purification weight estimation step of 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
[
Math
.
50
]
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.
4. The sound signal purification method according to claim 1 , further comprising
an n-th channel purification weight estimation step of obtaining,
for the each frame with respect to the each channel n,
a value that is larger than 0 and smaller than 1, 0.5 when b n and b M are equal, closer to 0 than 0.5 as b n is larger than b M , and closer to 1 than 0.5 as b M is larger than b n by using at least 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 .
5. The sound signal purification method according to claim 1 , further comprising
an n-th channel purification weight estimation step of 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 for the n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn 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
[
Math
.
51
]
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 .
6. The sound signal purification method according to claim 1 , further comprising
an n-th channel purification weight estimation step of 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 ,
a value c n ×r n obtained by multiplying
r n that is a value closer to 1 as a correlation between the n-th channel decoded sound signal {circumflex over ( )}X n and the n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn is higher, and closer to 0 as the correlation is lower by
a correction coefficient c n that is a value larger than 0 and smaller than 1, 0.5 when b n and b M are same, closer to 0 than 0.5 as b n is larger than b M , and closer to 1 than 0.5 as b n is smaller than b M , as the n-th channel purification weight α n .
7. 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 Mn is a value larger than 0 and smaller than 1, and
the sound signal purification method further comprises
an n-th channel purification weight estimation step of 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 Mn (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
^
Mn
(
t
)
[
Math
.
52
]
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 Mn (t) of the n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn , and an inner product value E n (−1) of a previous frame, and
energy E Mn (0) of the n-th channel upmixed monaural decoded sound signal obtained by
E
Mn
(
0
)
=
ϵ
Mn
E
Mn
(
-
1
)
+
(
1
-
ϵ
Mn
)
T
∑
t
=
1
T
x
^
Mn
(
t
)
x
^
Mn
(
t
)
[
Math
.
53
]
using the each sample value {circumflex over ( )}X Mn (t) of the n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn and energy E Mn (−1) of the n-th channel upmixed 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
[
Math
.
55
]
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 .
8. The sound signal purification method according to claim 5 , wherein
the n-th channel purification weight estimation step
obtains a value λ×c n ×r n obtained by multiplying the normalized inner product value r n , the correction coefficient c n , and λ that is a predetermined value larger than 0 and smaller than 1 as the n-th channel purification weight α n .
9. The sound signal purification method according to claim 5 , wherein
a number N of the channels is two, and
the n-th channel purification weight estimation step
obtains a value 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 that is a correlation coefficient between the first channel decoded sound signal and the second channel decoded sound signal as the n-th channel purification weight α n .
10. 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 .
11. A sound signal purification device for obtaining, for each frame, an n-th channel purified decoded sound signal {circumflex over ( )}X n that is a sound signal of each channel of stereo 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) that is a decoded sound signal of the each channel of the stereo obtained by decoding a stereo code CS and a monaural decoded sound signal {circumflex over ( )}X M that is a monaural decoded sound signal obtained by decoding a monaural code CM that is a code different from the stereo code CS, wherein
the n-th channel decoded sound signal {circumflex over ( )}X n is obtained by decoding the stereo code CS without using either information obtained by decoding the monaural code CM or the monaural code CM, and
the sound signal purification device further comprises
a monaural decoded sound upmixing circuitry configured to obtain, for the each frame, an n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn that is a signal obtained by upmixing the monaural decoded sound signal {circumflex over ( )}X M for the each channel by an upmixing process using the monaural decoded sound signal {circumflex over ( )}X M and inter-channel relationship information that is information indicating a relationship between the channels of the stereo, and
an n-th channel signal purification circuitry configured to obtain, for the each frame and for each corresponding sample t with respect to the each channel n, a sequence based on a value {circumflex over ( )}x n (t)=(1−α n )×{circumflex over ( )}x n (t)+α n ×{circumflex over ( )}x Mn (t) obtained by adding a value α n ×{circumflex over ( )}x Mn (t) obtained by multiplying an n-th channel purification weight α n by a sample value {circumflex over ( )}x Mn (t) of the n-th channel upmixed monaural decoded sound signal {circumflex over ( )}X Mn and a value (1−a n )×{circumflex over ( )}x n (t) obtained by multiplying a value (1−a 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 {circumflex over ( )}X n .
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 .
13. A non-transitory recording medium recording a program for causing a computer to execute processing of the steps of the sound signal purification method according to claim 1 .