Converting M channels of digital audio data into N channels of digital audio data
View Patent ↗Audio data having M channels includes a header with metadata specifying a conversion function for converting the M channels of digital audio data into N channels of data. The metadata is a string of coefficients, which may be specified by the content author, to define to conversion of the M channels of digital audio data into N channels.
1. A computer readable medium having computer executable instructions stored thereon, the medium comprising:
audio data having M channels and including a header wherein the header includes metadata specifying a conversion function for converting the M channels of the audio data into N channels of data;
wherein the conversion function is a fold-down function specified by the metadata which includes a plurality of coefficients which define a conversion of a Y audio data set having M channels (Y 1 –Y M channels) to an X audio data set having N channels (X 1 –X N channels);
wherein the coefficients comprise coefficients K Aj which define the fold-down as follows:
X
A
=
∑
j
=
1
M
K
Aj
Y
j
(
for
A
=
1
to
N
)
;
wherein the audio data comprises a 5.1 audio stream having six channels having left front, right front, center, low frequency, left surround and right surround channels such that M=6, wherein the destination device comprises a stereo destination device having left and right channels such that N=2, wherein the coefficients include B, SMIX, CMIX and LFEMIX and wherein the fold-down function comprises:
L ( N )= B*[L ( M )+ SMIX*LS ( M )+ CMIX*C ( M )+ LFEMIX*LFE ( M )]
and
R ( N )= B*[R ( M )+ SMIX*RS ( M )+ CMIX*C ( M )+ LFEMIX*LFE ( M )]
wherein:
L(N) is the data for the left channel of the stereo destination device;
L(M) is the left front channel data of the 5.1 audio stream;
LS(M) is the left surround channel data of the 5.1 audio stream;
C(M) is the center channel data of the 5.1 audio stream;
LFE(M) is the low frequency channel data of the 5.1 audio stream;
R(N) is the data for the right channel of the stereo destination device;
R(M) is the right front channel data of the 5.1 audio stream; and
RS(M) is the right surround channel data of the 5.1 audio stream; and
wherein B=1/(1+SMIX+CMIX+LFEMIX).
2. A computer readable medium having computer executable instructions stored thereon, the medium comprising:
audio data having M channels and including a header wherein the header includes metadata specifying a conversion function for converting the M channels of the audio data into N channels of data;
wherein the conversion function is a fold-down function specified by the metadata which includes a plurality of coefficients which define a conversion of a Y audio data set having M channels (Y 1 –Y M channels) to an X audio data set having N channels (X 1 –X N channels)
wherein the coefficients comprise coefficients K Aj which define the fold-down as follows:
X
A
=
∑
j
=
1
M
K
Aj
Y
j
(
for
A
=
1
to
N
)
;
wherein the audio data comprises a 5.1 audio stream having six channels having left front right front, center, low frequency, left surround and right surround channels such that M=6, wherein the destination device comprises a stereo destination device having left and right channels such that N=2, wherein the coefficients include B, SMIX, CMIX and LYEMIX and wherein the fold-down function comprises:
L ( N )= B*[R ( M )+ SMIX*LS ( M )+ CMIX*C ( M )+ LFEMIX*LFE ( M )]
and
R ( N )= B*[R ( M )+ SMIX*RS ( M )+ CMIX*C ( M )+ LFEMIX*LFE ( M )]
wherein:
L(N) is the data for the left channel of the stereo destination device;
L(M) is the left front channel data of the 5.1 audio stream;
LS(M) is the left surround channel data of the 5.1 audio stream;
C(M) is the center channel data of the 5.1 audio stream;
LFE(M) is the low frequency channel data of the 5.1 audio stream;
R(N) is the data for the right channel of the stereo destination device;
R(M) is the right front channel data of the 5.1 audio stream; and
RS(M) is the right surround channel data of the 5.1 audio stream; and
wherein the fold-down function is based on the following mix table wherein;
L(M)
R(M)
C(M)
LFE(M)
LS(M)
RS(M)
L(N)
W
−INFINITY
Y
Z
X
−INFINITY
R(N)
−INFI-
W
Y
Z
−INFI-
X
NITY
NITY
wherein:
W=20*65536*log 10 (B);
X=20*65536*log 10 (SMIX*B);
Y=20*65536*log 10 (CMIX*B);
Z=20*65536*log 10 (LFEMIX*B); and
−INFINITY represents negative infinity.
3. The medium of claim 2 wherein the metadata includes the following string format representation for the mix table:
W,−INFINTE,−INFINTE,W,Y,Y,Z,Z,X,−INFINTE,−INFNITE,X.
4. The medium of claim 1 wherein the conversion function is specified in a separate data stream of the audio data and may be continuously varying.
5. The medium of claim 1 wherein a metadata name for the conversion function comprises “Fold % dto % DChannels % C” where % d represents M, % D represents N and % C represents a channel mask.
6. The medium of claim 1 wherein the metadata comprises a channel mask.
7. The medium of claim 2 wherein the conversion function is specified in a separate data stream of the audio data and may be continuously varying.
8. The medium of claim 2 wherein a metadata name for the conversion function comprises “Fold % dto % DChannels % C” where % d represents M, % D represents N and % C represents a channel mask.
9. The medium of claim 2 wherein the metadata comprises a channel mask.
10. The medium of claim 3 wherein the conversion function is specified in a separate data stream of the audio data and may be continuously varying.
11. The medium of claim 3 wherein a metadata name for the conversion function comprises “Fold % dto % DChannels % C” where % d represents M, % D represents N and % C represents a channel mask.
12. The medium of claim 3 wherein the metadata comprises a channel mask.