Method for generating a downward-compatible sound format
A method of generating an audio output signal according to a downward compatible sound format, the method including: generating a sum signal by combining a first input channel signal with a second input channel signal; and dynamically correcting the sum signal using samples of the first and second input channel signals from overlapping time windows.
1. A method of generating a downward compatible two-channel sound format having a right channel (R lRT ) and a left channel (L lRT ) from a five channel sound format having the following sound channels:
left channel (L)
right channel (R)
centre channel (C)
rear left channel (Ls)
rear right channel (Rs),
whereas
the level of the centre channel (C) is lowered,
the level of the centre channel (C) is distributed to the left channel (L) so as to form the left channel (L) so as to form a first sum signal (L′),
the level of the rear left channel (Ls) is lowered,
the rear left channel (Ls), the level of which has been lowered, is distributed to the first sum signal so as to form the third sum signal which corresponds to the left channel (L lRT ) of the two channel sound format,
the centre channel (C), the level of which has been lowered, is distributed to the right channel (R) so as to form a second sum signal (R′),
the level of the rear right channel (Rs) is lowered,
the rear right channel (Rs) the level of which has been lowered, is distributed to the second sum signal to form a fourth sum signal which corresponds to the right channel (R lRT ) of a two channel sound format,
wherein:
while forming the first sum signal (L′) and the second sum signal (R′) for spectral values of overlapping time windows each is dynamically corrected with k samples of the left channel (L) and the right channel (R), and
while forming the third and fourth sum signal for spectral values of overlapping time windows each is dynamically corrected with k samples of the first sum signal (L′) and the second sum signal (R′),
that before each dynamic correction of the spectral values of the left channel (L) and the right channel (R), every sum of the spectral values is compared with a desired value (A soll , with A soll R), which follows from the following relationship:
A soll,l ( k )=√{square root over (| l ( k )| 2 +|c ( k )| 2 )}{square root over (| l ( k )| 2 +|c ( k )| 2 )}
A soll,r ( k )=√{square root over (| r ( k )| 2 +|c ( k )| 2 )}{square root over (| r ( k )| 2 +|c ( k )| 2 )}
where
|l(k)| is the absolute value of a spectral value of the transformed left channel (L) in the complex plane C,
|c(k)| is the absolute value of the respective spectral value of the transformed centre channel (C) in the complex plane C,
|r(k)| is the absolute value of a spectral value of the transformed right channel (R) in the complex plane C,
that before each dynamic correction of the spectral values of the first sum signal (L′) and the second sum signal (R′), every sum of the spectral values is compared with a desired value (A soll , with A soll R), which follows from the following relationship:
A soll,ls ( k )=√{square root over (| l′ ( k )| 2 +|ls ( k )| 2 )}{square root over (| l′ ( k )| 2 +|ls ( k )| 2 )}
A soll,rs ( k )=√{square root over (| r′ ( k )| 2 +|rs ( k )| 2 )}{square root over (| r′ ( k )| 2 +|rs ( k )| 2 )}
where
|r′(k)| is the absolute value of the spectral values of the transformed third sum signal (R′) in the complex plane C,
|l′(k)| is the absolute value of the respective spectral values of the transformed first sum signal (L′) in the complex plane C,
|rs(k)| is the absolute value of the spectral values of the transformed rear right channel (Rs) in the complex plane C,
|ls(k)| is the absolute value of the respective spectral values transformed rear left channel (Ls) in the complex plane C,
that in case the desired value (A soll ) is exceeded, the frequency component is added and the resulting sum is lowered according to
S ( k )= A soll ( k )+(| A ( k )+ B ( k )|− A soll ( k ))* n
and for the case that the desired value (A soll ) is undercut, the spectral values of the respective signal is multiplied with the following multiplier (m(k), with m(k) R):
m
(
k
)
=
-
p
+
w
·
p
2
+
(
A
(
k
)
)
4
A
(
k
)
2
where
A(k) is the k-th spectral value of r′, l′, l and r, with A(k) C,
p =R(A(k))·R(B(k))+ℑ(A(k))·ℑ(B(k)),
B(k) is the k-th spectral value of rs, ls, and c, with B(k) C, and
w is a scaling factor ranging from −1<w<1, where w R.
2. A method of generating an audio output signal according to a downward compatible sound format, the method comprising:
generating a sum signal by combining a first input channel signal with a second input channel signal; and
dynamically correcting the sum signal using samples of the first and second input channel signals from overlapping time windows to produce the audio output signal, the dynamically correcting comprising correcting each sample s of the sum signal based on a comparison to a desired value A soll for the sample.
3. The method recited in claim 2 , wherein for each sample,
s ( k )=| A ( k )+ B ( k )|, and
A soll ( k )=√{square root over (| A ( k )| 2 +|B ( k )| 2 )}{square root over (| A ( k )| 2 +|B ( k )| 2 )},
where:
k is the sample number, and
A(k) and B(k) are spectral values, respectively, of the transformed first and second channel signals in the complex plane C for the sample k.
4. The method recited in claim 3 , wherein
if the sum signal s for a given sample k is greater than the desired value A soll for the sample k, the spectral value S(k) of the audio output signal is determined by:
S ( k )= A soll ( k )+(| A ( k )+ B ( k )|− A soll ( k ))* n,
otherwise, S(k) is determined by:
S ( k )=m( k )* A ( k )+ B ( k ),
where
n and m are multiplying factors.
5. The method recited in claim 4 , wherein
n is a predetermined multiplying factor between 0.1 and 0.4, and
m
(
k
)
=
-
p
+
w
·
p
2
+
(
A
(
k
)
)
4
A
(
k
)
2
,
where
p =R(A(k))·R(B(k))+ℑ(A(k))·ℑ(B(k)), and
w is a scaling factor between −1 and 1.
6. A method of generating an audio output signal according to a downward compatible sound format, the method comprising:
combining a left input channel signal L with a center input channel signal C;
dynamically correcting the L/C signal combination using samples of the left input channel signal L and the center input channel signal C from overlapping time windows to produce a left sum signal L′;
combining a right input channel signal R with the center input channel signal C, the center input channel signal C being lowered before being combined with the left input channel signal L or the right input channel signal R; and
dynamically correcting the R/C signal combination using samples of the right input channel signal R and the center input channel signal C from overlapping time windows to produce a right sum signal R′.
7. The method recited in claim 6 , wherein dynamically correcting the L/C signal combination or dynamically correcting the R/C signal combination comprises correcting each sample S of the corresponding signal combination based on a comparison to a desired value A soll for the sample.
8. The method recited in claim 7 , wherein for dynamically correcting the L/C signal combination,
S l ( k )=| l ( k )+ c ( k )|, and
A soll,l ( k )=√{square root over (| l ( k )| 2 +|c ( k )| 2 )}{square root over (| l ( k )| 2 +|c ( k )| 2 )},
where:
k is the sample number, and
l(k) and c(k) are spectral values, respectively, of the transformed left and center input channels L and C in the complex plane C for the sample k.
9. The method recited in claim 8 , wherein
if the L/C signal combination S l for a given sample k is greater than the desired value A soll,l for the sample k, the spectral value l′(k) of the transformed left sum signal L′ is determined by:
l ( k )= A soll ( k )+(| l ( k )+ c ( k )|− A soll,l ( k ))* n,
otherwise, l′(k) is determined by:
l ( k )=m l ( k )* l ( k )+ c ( k ),
where
n and m l are multiplying factors.
10. The method recited in claim 9 , wherein
n is a predetermined multiplying factor between 0.1 and 0.4, and
m
l
(
k
)
=
-
p
+
w
·
p
2
+
(
l
(
k
)
)
4
l
(
k
)
2
,
where
p =R(l(k))·R(c(k))+ℑ(l(k))·ℑ(c(k)), and
w is a scaling factor between −1 and 1.
11. The method recited in claim 7 , wherein for dynamically correcting the R/C signal,
S r ( k )=| r ( k )+ c ( k )|, and
A soll,r ( k )=√{square root over (| r ( k )| 2 +|c ( k )| 2 )}{square root over (| r ( k )| 2 +|c ( k )| 2 )},
where:
k is the sample number, and
r(k) and c(k) are spectral values, respectively, of the transformed right and center input channels R and C in the complex plane C for the sample k.
12. The method recited in claim 11 , wherein
if the R/C signal combination S r for a given sample k is greater than the desired value A soll,r for the sample k, the spectral value r′(k) of the transformed right sum signal R′ is determined by:
r′ ( k )= A soll,r ( k )+(| r ( k )+ c ( k )|− A soll,r ( k ))* n,
otherwise, r′(k) is determined by:
r ( k )=m r ( k )* r ( k )+ c ( k ),
where
n and m r are multiplying factors.
13. The method recited in claim 12 , wherein
n is a predetermined multiplying factor between 0.1 and 0.4, and
m
r
(
k
)
=
-
p
+
w
·
p
2
+
(
r
(
k
)
)
4
r
(
k
)
2
,
where
p =R(r(k))·R(c(k))+ℑ(r(k))·ℑ(c(k)), and
w is a scaling factor between −1 and 1.
14. The method recited in claim 6 , further comprising:
combining the left sum signal L′ with a rear left input channel signal Ls;
dynamically correcting the L′/Ls signal combination using samples of the left sum signal L′ and the rear left input channel signal Ls from overlapping time windows to produce a left output signal L lRT ;
combining the right sum signal R′ with a rear right input channel signal Rs; and
dynamically correcting the R′/Rs signal combination using samples of the right sum signal R′ and the rear right input channel signal Rs from overlapping time windows to produce a right output signal R lRT .
15. The method recited in claim 14 , wherein the rear left input channel signal Ls and the rear right input channel signal Rs are lowered before being respectively combined with the left sum signal L′ and the right sum signal R′.
16. The method recited in claim 14 , wherein dynamically correcting the L′/Ls signal combination or the R′/Rs signal combination comprises correcting each sample S of the corresponding signal combination based on a comparison to a desired value A soll for the sample.
17. The method recited in claim 16 , wherein for dynamically correcting the L′/Ls signal combination,
S ls ( k )=| l′ ( k )+ ls ( k )|, and
A soll,ls ( k )=√{square root over (| l′ ( k )| 2 +|ls ( k )| 2 )}{square root over (| l′ ( k )| 2 +|ls ( k )| 2 )},
where:
k is the sample number, and
l′(k) and ls(k) are spectral values, respectively, of the transformed left sum signal L′ and rear left input channel Ls in the complex plane C for the sample k.
18. The method recited in claim 17 , wherein
if the L′/Ls signal combination S ls for a given sample k is greater than the desired value A soll,ls for the sample k, the spectral value l lRT (k) of the left output signal L lRT is determined by:
l lRT ( k )= A soll,ls ( k )+(| l′ ( k )+ ls ( k )|− A soll,ls ( k ))* n,
otherwise, l lRT (k) is determined by:
l lRT ( k )=m ls ( k )* l′ ( k )+ ls ( k ),
where
n and m ls are multiplying factors.
19. The method recited in claim 18 , wherein
n is a predetermined multiplying factor between 0.1 and 0.4, and
m
ls
(
k
)
=
-
p
+
w
·
p
2
+
(
l
′
(
k
)
)
4
l
′
(
k
)
2
,
where
p =R(l′(k))·R(ls(k))+ℑ(l′(k))·ℑ(ls(k)), and
w is a scaling factor between −1 and 1.
20. The method recited in claim 16 , wherein for dynamically correcting the R′/Rs signal combination,
S rs ( k )=| r′ ( k )+ rs ( k )|, and
A soll,rs ( k )=√{square root over (| r′ ( k )| 2 +|rs ( k )| 2 )}{square root over (| r′ ( k )| 2 +|rs ( k )| 2 )},
where:
k is the sample number,
r′(k) and rs(k) are spectral values, respectively, of the transformed right sum signal R′ and rear right input channel Rs in the complex plane C for the sample k.
21. The method recited in claim 20 , wherein
if the R′/Rs signal combination S rs for a given sample k is greater than the desired value A soll,rs for the sample k, the spectral value r lRT (k) of the right output signal R lRT is determined by:
r lRT ( k )=A soll,rs ( k )+(| r′ ( k )+ rs ( k )|− A soll,rs ( k ))* n,
otherwise, r lRT (k) is determined by:
r lRT ( k )=m rs s( k )* r′ ( k )+ rs ( k ),
where
n and m rs are multiplying factors.
22. The method recited in claim 21 , wherein
n is a predetermined multiplying factor between 0.1 and 0.4, and
m
rs
(
k
)
=
-
p
+
w
·
p
2
+
(
r
′
(
k
)
)
4
r
′
(
k
)
2
,
where
p =R(r′(k))·R(rs(k))+ℑ(r′(k))·ℑ(rs(k)), and
w is a scaling factor between −1 and 1.
23. An audio playback apparatus comprising:
a first input channel that receives a first input signal;
a second input channel that receives a second input signal;
an output channel that outputs an output signal, the output signal being at least partially determined by combining the first input signal and the second input signal to generate a sum signal and dynamically correcting the sum signal using samples of the first and second input channels from overlapping time windows, the dynamically correcting comprising correcting each sample s of the sum signal based on a comparison to a desired value A soll for the sample.
24. An audio playback apparatus comprising:
a left input channel that receives a left input signal L;
a right input channel that receives a right input signal R;
a center input channel that receives a center input signal C;
a left output channel that outputs a left output signal L lRT , the left output signal L lRT being at least partially determined by combining the left input signal L and the center input signal C and dynamically correcting the L/C signal combination using samples of the left input signal L and the center input signal C from overlapping time windows; and
a right output channel that outputs a right output signal R lRT , the right output signal R lRT being at least partially determined by combining the right input signal R and the center input signal C and dynamically correcting the R/C signal combination using samples of the right input signal R and the center input signal C from overlapping time windows, the center input channel signal C being lowered before being combined with the left input channel signal L or the right input channel signal R.
25. The audio playback apparatus recited in claim 24 , further comprising:
a rear left input channel that receives a rear left input signal Ls;
a rear right input channel that receives a rear right input signal Rs;
wherein:
the left output signal L lRT is further determined by combining the dynamically corrected L/C signal combination L′ and the rear left input signal Ls and dynamically correcting the L′/Ls signal combination using samples of the dynamically corrected L/C signal combination L′ and the rear left input signal Ls from overlapping time windows; and
the right output signal R lRT is further determined by combining the dynamically corrected R/C signal combination R′ and the rear right input signal Rs and dynamically correcting the R′/Rs signal combination using samples of the dynamically corrected R/C signal combination R′ and the rear right input signal Rs from overlapping time windows.