Version
The downmixing equations are based on AC-3 standards. They have been designed to end up the same regardless of whether signals are downmixed directly (for example, 7.1 to stereo) or in several successive steps (for example, 7.1 to 5.1 to stereo).
Consider the following table, describing the downmix equations used when routing a 5.1 input to a stereo output.
Sample table: Routing 5.1 to stereo
|
Input Channels |
L |
R |
|---|---|---|
|
FL |
1 |
0 |
|
FR |
0 |
1 |
|
C |
1/√2 |
1/√2 |
|
SL |
1/√2 |
0 |
|
SR |
0 |
1/√2 |
The left and right channels of the resulting stereo signal are the weighted sum of the inputs into these equations:
LOUT = FL + 1/√2 * C + 1/√2 * SL
ROUT = FR + 1/√2 * C + 1/√2 * SR
Like the above formula, you can calculate the output signal for each downmixed format by adding up the totals of each output channel column in the following reference downmix tables:
To Mono
|
Input Channels |
C |
|---|---|
|
FL |
1/√2 |
|
FR |
1/√2 |
|
C |
1 |
|
SL |
1/2 |
|
SR |
1/2 |
|
BL |
1/2 |
|
BR |
1/2 |
|
Top |
1 |
|
HFL |
1/2 |
|
HFC |
1/√2 |
|
HFR |
1/2 |
|
HBL |
1/(2√2) |
|
HBR |
1/(2√2) |
To Stereo
|
Input Channels |
L |
R |
|---|---|---|
|
FL |
1 |
0 |
|
FR |
0 |
1 |
|
C |
1/√2 |
1/√2 |
|
SL |
1/√2 |
0 |
|
SR |
0 |
1/√2 |
|
BL |
1/√2 |
0 |
|
BR |
0 |
1/√2 |
|
Top |
1/√2 |
1/√2 |
|
HFL |
1/√2 |
0 |
|
HFC |
1/2 |
1/2 |
|
HFR |
0 |
1/√2 |
|
HBL |
1/2 |
0 |
|
HBR |
0 |
1/2 |
To 3.x
|
Input Channels |
L |
R |
C |
|---|---|---|---|
|
FL |
1 |
0 |
0 |
|
FR |
0 |
1 |
0 |
|
C |
0 |
0 |
1 |
|
SL |
1/√2 |
0 |
0 |
|
SR |
0 |
1/√2 |
0 |
|
BL |
1/√2 |
0 |
0 |
|
BR |
0 |
1/√2 |
0 |
|
Top |
1/√3 |
1/√3 |
1/√3 |
|
HFL |
1/√2 |
0 |
0 |
|
HFC |
0 |
0 |
1/√2 |
|
HFR |
0 |
1/√2 |
0 |
|
HBL |
1/2 |
0 |
0 |
|
HBR |
0 |
1/2 |
0 |
To 4.x
|
Input Channels |
L |
R |
SL |
SR |
|---|---|---|---|---|
|
FL |
1 |
0 |
0 |
0 |
|
FR |
0 |
1 |
0 |
0 |
|
C |
1/√2 |
1/√2 |
0 |
0 |
|
SL |
0 |
0 |
1 |
0 |
|
SR |
0 |
0 |
0 |
1 |
|
BL |
0 |
0 |
1 |
0 |
|
BR |
0 |
0 |
0 |
1 |
|
Top |
1/2 |
1/2 |
1/2 |
1/2 |
|
HFL |
1/√2 |
0 |
0 |
0 |
|
HFC |
1/2 |
1/2 |
0 |
0 |
|
HFR |
0 |
1/√2 |
0 |
0 |
|
HBL |
0 |
0 |
1/√2 |
0 |
|
HBR |
0 |
0 |
0 |
1/√2 |
To 5.x
|
Input Channels |
L |
R |
C |
SL |
SR |
|---|---|---|---|---|---|
|
FL |
1 |
0 |
0 |
0 |
0 |
|
FR |
0 |
1 |
0 |
0 |
0 |
|
C |
0 |
0 |
1 |
0 |
0 |
|
SL |
0 |
0 |
0 |
1 |
0 |
|
SR |
0 |
0 |
0 |
0 |
1 |
|
BL |
0 |
0 |
0 |
1 |
0 |
|
BR |
0 |
0 |
0 |
0 |
1 |
|
Top |
1/√5 |
1/√5 |
1/√5 |
1/√5 |
1/√5 |
|
HFL |
1/√2 |
0 |
0 |
0 |
0 |
|
HFC |
0 |
0 |
1/√2 |
0 |
0 |
|
HFR |
0 |
1/√2 |
0 |
0 |
0 |
|
HBL |
0 |
0 |
0 |
1/√2 |
0 |
|
HBR |
0 |
0 |
0 |
0 |
1/√2 |
To 6.x
|
Input Channels |
L |
R |
SL |
SR |
BL |
BR |
|---|---|---|---|---|---|---|
|
FL |
1 |
0 |
0 |
0 |
0 |
0 |
|
FR |
0 |
1 |
0 |
0 |
0 |
0 |
|
C |
1/√2 |
1/√2 |
0 |
0 |
0 |
0 |
|
SL |
0 |
0 |
1 |
0 |
0 |
0 |
|
SR |
0 |
0 |
0 |
1 |
0 |
0 |
|
BL |
0 |
0 |
0 |
0 |
1 |
0 |
|
BR |
0 |
0 |
0 |
0 |
0 |
1 |
|
Top |
1/√6 |
1/√6 |
1/√6 |
1/√6 |
1/√6 |
1/√6 |
|
HFL |
1/√2 |
0 |
0 |
0 |
0 |
0 |
|
HFC |
1/2 |
1/2 |
0 |
0 |
0 |
0 |
|
HFR |
0 |
1/√2 |
0 |
0 |
0 |
0 |
|
HBL |
0 |
0 |
0 |
0 |
1/√2 |
0 |
|
HBR |
0 |
0 |
0 |
0 |
0 |
1/√2 |
To 7.x
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