Method and apparatus for generating and restoring downmixed signal
An embodiment of the present invention provides a method for generating a downmixed signal, including: performing a time-frequency transform on a received left sound channel signal and a received right sound channel signal to obtain a frequency domain signal, and dividing the frequency domain signal into several frequency bands; calculating a sound channel energy ratio and a sound channel phase difference of each frequency band; calculating a phase difference between the downmixed signal and a first sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference; and calculating a frequency domain downmixed signal according to the left sound channel signal, the right sound channel signal, and the phase difference between the downmixed signal and the first sound channel signal in each frequency band. This method effectively improves quality of stereo encoding and decoding.
1. A method for generating a downmixed signal, the method comprising:
performing a time-frequency transform on a left sound channel signal and a right sound channel signal to obtain a frequency domain signal, and dividing the frequency domain signal into several frequency bands;
calculating a sound channel energy ratio and a sound channel phase difference of each frequency band, wherein the sound channel energy ratio reflects energy ratio information of the left sound channel signal and the right sound channel signal in each frequency band, and the sound channel phase difference reflects phase difference information of the left sound channel signal and the right sound channel signal in each frequency band;
calculating a phase difference between the downmixed signal and a first sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference, wherein the first sound channel signal is the left sound channel signal or the right sound channel signal; and
calculating a frequency domain downmixed signal according to the left sound channel signal, the right sound channel signal, and the phase difference between the downmixed signal and the first sound channel signal in each frequency band;
wherein the first sound channel signal is a signal having a greater signal amplitude in the left sound channel signal and the right sound channel signal, and calculating a phase difference between the downmixed signal and a first sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference comprises: calculating the phase difference between the downmixed signal and the signal having the greater signal amplitude in the left sound channel signal and the right sound channel signal according to the sound channel energy ratio and the sound channel phase difference.
2. A method for generating a downmixed signal, the method comprising:
performing a time-frequency transform on a left sound channel signal and a right sound channel signal to obtain a frequency domain signal, and dividing the frequency domain signal into several frequency bands;
calculating a sound channel energy ratio and a sound channel phase difference of each frequency band, wherein the sound channel energy ratio reflects energy ratio information of the left sound channel signal and the right sound channel signal in each frequency band, and the sound channel phase difference reflects phase difference information of the left sound channel signal and the right sound channel signal in each frequency band;
calculating a phase difference between the downmixed signal and a first sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference, wherein the first sound channel signal is the left sound channel signal or the right sound channel signal; and
calculating a frequency domain downmixed signal according to the left sound channel signal, the right sound channel signal, and the phase difference between the downmixed signal and the first sound channel signal in each frequency band;
wherein the first sound channel is the left sound channel, and calculating a phase difference between the downmixed signal and a first sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference comprises performing calculation according to the following formulas:
c
(
b
)
=
10
CLD
(
b
)
/
10
;
and
θ
(
b
)
=
1
1
+
c
(
b
)
·
IPD
(
b
)
,
wherein CLD(b) is the sound channel energy ratio of a b th frequency band, c(b) is an intermediate value variable for calculation, IPD(b) is the sound channel phase difference of the b th frequency band, and θ(b) is a phase difference between the downmixed signal and the first sound channel signal in the b th frequency band.
3. The method according to claim 2 , wherein the first sound channel is the left sound channel, and calculating a frequency domain downmixed signal according to the left sound channel signal, the right sound channel signal, and the phase difference between the downmixed signal and the first sound channel signal in each frequency band comprises performing calculation according to the following formulas:
M
r
(
k
)
=
0.5
(
1
+
R
mag
(
k
)
L
mag
(
k
)
)
(
L
r
(
k
)
cos
(
θ
(
b
)
)
+
L
i
(
k
)
sin
(
θ
(
b
)
)
)
;
and
M
i
(
k
)
=
0.5
(
1
+
R
mag
(
k
)
L
mag
(
k
)
)
(
L
i
(
k
)
cos
(
θ
(
b
)
)
-
L
r
(
k
)
sin
(
θ
(
b
)
)
)
,
wherein k is a frequency point index, L r (k) is a real part of the left sound channel signal at a k th frequency point after time-frequency transform, L i (k) is an imaginary part of the left sound channel signal at the k th frequency point after the time-frequency transform, R mag (k) is an amplitude of the right sound channel signal at the k th frequency point after the time-frequency transform, L mag (k) is an amplitude of the left sound channel signal at the k th frequency point after the time-frequency transform, M i (k) is a real part of the downmixed signal at the k th frequency point after the time-frequency transform, M r (k) is an imaginary part of the downmixed signal at the k th frequency point after the time-frequency transform, and θ(b) is the phase difference between the downmixed signal and the first sound channel signal in the b th frequency band.
4. The method according to claim 3 , wherein:
after calculating a phase difference between the downmixed signal and a first sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference, the method further comprises:
updating the phase difference between the downmixed signal and the first sound channel signal in each frequency band according to a group phase, wherein the group phase reflects similarity between frequency domain envelopes of the left sound channel signal and the right sound channel signal; and
calculating a frequency domain downmixed signal according to the left sound channel signal, the right sound channel signal, and the phase difference between the downmixed signal and the first sound channel signal in each frequency band comprises:
calculating the frequency domain downmixed signal according to the left sound channel signal, the right sound channel signal, and updated phase difference between the downmixed signal and the first sound channel signal in each frequency band.
5. A method for generating a downmixed signal, the method comprising:
performing a time-frequency transform on a left sound channel signal and a right sound channel signal to obtain a frequency domain signal, and dividing the frequency domain signal into several frequency bands;
calculating a sound channel energy ratio and a sound channel phase difference of each frequency band, wherein the sound channel energy ratio reflects energy ratio information of the left sound channel signal and the right sound channel signal in each frequency band, and the sound channel phase difference reflects phase difference information of the left sound channel signal and the right sound channel signal in each frequency band;
calculating a phase difference between the downmixed signal and a first sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference, wherein the first sound channel signal is the left sound channel signal or the right sound channel signal; and
calculating a frequency domain downmixed signal according to the left sound channel signal, the right sound channel signal, and the phase difference between the downmixed signal and the first sound channel signal in each frequency band;
wherein the first sound channel is the right sound channel, and calculating a phase difference between the downmixed signal and a first sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference comprises performing calculation according to the following formulas:
c
(
b
)
=
10
CLD
(
b
)
/
10
;
and
θ
(
b
)
=
c
(
b
)
1
+
c
(
b
)
·
IPD
(
b
)
,
wherein CLD(b) is the sound channel energy ratio of a b th frequency band, c(b) is an intermediate value variable for calculation, IPD(b) is the sound channel phase difference of the b th frequency band, and θ(b) is a phase difference between the downmixed signal and the first sound channel signal in the b th frequency band.
6. The method according to claim 5 , wherein the first sound channel is the right sound channel, and calculating a frequency domain downmixed signal according to the left sound channel signal, the right sound channel signal, and the phase difference between the downmixed signal and the first sound channel signal in each frequency band comprises performing calculation according to the following formulas:
M
i
(
k
)
=
0.5
(
1
+
L
mag
(
k
)
R
mag
(
k
)
)
(
R
i
(
k
)
cos
(
θ
(
b
)
)
+
R
r
(
k
)
sin
(
θ
(
b
)
)
)
;
and
M
r
(
k
)
=
0.5
(
1
+
L
mag
(
k
)
R
mag
(
k
)
)
(
R
r
(
k
)
cos
(
θ
(
b
)
)
-
R
i
(
k
)
sin
(
θ
(
b
)
)
)
,
wherein k is a frequency point index, R r (k) is a real part of the right sound channel signal at a k th frequency point after time-frequency transform, R i (k) is an imaginary part of the right sound channel signal at the k th frequency point after the time-frequency transform, R mag (k) is an amplitude of the right sound channel signal at the k th frequency point after the time-frequency transform, L mag (k) is an amplitude of the left sound channel signal at the k th frequency point after the time-frequency transform, M i (k) is a real part of the downmixed signal at the k th frequency point after the time-frequency transform, M r (k) is an imaginary part of the downmixed signal at the k th frequency point after the time-frequency transform, and θ(b) is the phase difference between the downmixed signal and the first sound channel signal in the b th frequency band.
7. An apparatus for generating a downmixed signal, the apparatus comprising:
a processor; and
a non-transitory computer-readable medium coupled to the processor and storing programming instructions for execution by the processor, the programming instructions instruct the processor to:
perform a time-frequency transform on a received left sound channel signal and a received right sound channel signal to obtain a frequency domain signal, and divide the frequency domain signal into several frequency bands;
calculate a sound channel energy ratio and a sound channel phase difference of each frequency band, wherein the sound channel energy ratio reflects energy ratio information of the left sound channel signal and the right sound channel signal in each frequency band, and the sound channel phase difference reflects phase difference information of the left sound channel signal and the right sound channel signal in each frequency band;
calculate a phase difference between the downmixed signal and a first sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference, wherein the first sound channel signal is the left sound channel signal or the right sound channel signal;
calculate a frequency domain downmixed signal according to the left sound channel signal, the right sound channel signal, and the phase difference between the downmixed signal and the first sound channel signal in each frequency band; and
calculate the phase difference between the downmixed signal and a sound channel signal having a greater amplitude in the left sound channel signal and the right sound channel signal in each frequency band according to the sound channel energy ratio and the sound channel phase difference.
8. The apparatus according to claim 7 , wherein the first sound channel is the right sound channel, and the programming instructions instruct the processor to calculate the phase difference between the downmixed signal and the first sound channel signal in each frequency band according to the following formulas:
c
(
b
)
=
10
CLD
(
b
)
/
10
;
and
θ
(
b
)
=
c
(
b
)
1
+
c
(
b
)
·
IPD
(
b
)
,
wherein CLD(b) is the sound channel energy ratio of a b th frequency band, c(b) is an intermediate value variable for calculation, IPD(b) is the sound channel phase difference of the bth frequency band, and θ(b) is a phase difference between the downmixed signal and the first sound channel signal in the bth frequency band.
9. The apparatus according to claim 8 , wherein the first sound channel is the left sound channel, and the programming instructions instruct the processor to calculate the frequency domain downmixed signal according to the following formulas:
M
r
(
k
)
=
0.5
(
1
+
R
mag
(
k
)
L
mag
(
k
)
)
(
L
r
(
k
)
cos
(
θ
(
b
)
)
+
L
i
(
k
)
sin
(
θ
(
b
)
)
)
;
and
M
i
(
k
)
=
0.5
(
1
+
R
mag
(
k
)
L
mag
(
k
)
)
(
L
i
(
k
)
cos
(
θ
(
b
)
)
-
L
r
(
k
)
sin
(
θ
(
b
)
)
)
,
wherein k is a frequency point index, L r (k) is a real part of the left sound channel signal at a kth frequency point after time-frequency transform, L i (k) is an imaginary part of the left sound channel signal at the kth frequency point after the time-frequency transform, R mag (k) is an amplitude of the right sound channel signal at the kth frequency point after the time-frequency transform, L mag (k) is an amplitude of the left sound channel signal at the kth frequency point after the time-frequency transform, M i (k) is a real part of the downmixed signal at the k th frequency point after the time-frequency transform, M r (k) is an imaginary part of the downmixed signal at the k th frequency point after the time-frequency transform, and θ(b) is the phase difference between the downmixed signal and the first sound channel signal in the b th frequency band.
10. The apparatus according to claim 7 , wherein the first sound channel is the left sound channel, and the programming instructions instruct the processor to calculate the phase difference between the downmixed signal and the first sound channel signal in each frequency band according to the following formulas:
c
(
b
)
=
10
CLD
(
b
)
/
10
;
and
θ
(
b
)
=
1
1
+
c
(
b
)
·
IPD
(
b
)
,
wherein CLD(b) is the sound channel energy ratio of a b th frequency band, c(b) is an intermediate value variable for calculation, IPD(b) is the sound channel phase difference of the b th frequency band, and θ(b) is a phase difference between the downmixed signal and the first sound channel signal in the b th frequency band.
11. The apparatus according to claim 10 , wherein the first sound channel is the right sound channel, and the programming instructions instruct the processor to calculate the frequency domain downmixed signal according to the following formulas:
M
i
(
k
)
=
0.5
(
1
+
L
mag
(
k
)
R
mag
(
k
)
)
(
R
i
(
k
)
cos
(
θ
(
b
)
)
+
R
r
(
k
)
sin
(
θ
(
b
)
)
)
;
and
M
r
(
k
)
=
0.5
(
1
+
L
mag
(
k
)
R
mag
(
k
)
)
(
R
r
(
k
)
cos
(
θ
(
b
)
)
-
R
i
(
k
)
sin
(
θ
(
b
)
)
)
,
wherein k is a frequency point index and is a natural number, R r (k) is a real part of the right sound channel signal at a k th frequency point after time-frequency transform, R i (k) is an imaginary part of the right sound channel signal at the k th frequency point after the time-frequency transform, R mag (k) is an amplitude of the right sound channel signal at the k th frequency point after the time-frequency transform, L mag (k) is an amplitude of the left sound channel signal at the k th frequency point after the time-frequency transform, M i (k) is a real part of the downmixed signal at the k th frequency point after the time-frequency transform, M r (k) is an imaginary part of the downmixed signal at the k th frequency point after the time-frequency transform, and θ(b) is the phase difference between the downmixed signal and the first sound channel signal in the b th frequency band.
12. The apparatus according to claim 9 wherein the programming instructions instruct the processor to update the phase difference between the downmixed signal and the first sound channel according to a group phase, wherein the group phase reflects similarity between frequency domain envelopes of the left sound channel signal and the right sound channel signal.