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Downmix Tables

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).

How to read the downmix tables

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 ChannelsLR
 ExactDecimaldBExactDecimaldB
FL11.0000.0000.000−∞
FR00.000−∞11.0000.00
C1/√20.707−3.011/√20.707−3.01
SL1/√20.707−3.0100.000−∞
SR00.000−∞1/√20.707−3.01

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

Reference Tables

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 ChannelsC
 ExactDecimaldB
FL1/√20.707−3.01
FR1/√20.707−3.01
C11.0000.00
SL1/20.500−6.02
SR1/20.500−6.02
BL1/20.500−6.02
BR1/20.500−6.02
Top11.0000.00
HFL1/20.500−6.02
HFC1/√20.707−3.01
HFR1/20.500−6.02
HBL1/(2√2)0.354−9.03
HBR1/(2√2)0.354−9.03

To Stereo

Input ChannelsLR
 ExactDecimaldBExactDecimaldB
FL11.0000.0000.000−∞
FR00.000−∞11.0000.00
C1/√20.707−3.011/√20.707−3.01
SL1/√20.707−3.0100.000−∞
SR00.000−∞1/√20.707−3.01
BL1/√20.707−3.0100.000−∞
BR00.000−∞1/√20.707−3.01
Top1/√20.707−3.011/√20.707−3.01
HFL1/√20.707−3.0100.000−∞
HFC1/20.500−6.021/20.500−6.02
HFR00.000−∞1/√20.707−3.01
HBL1/20.500−6.0200.000−∞
HBR00.000−∞1/20.500−6.02

To 3.x

Input ChannelsLRC
 ExactDecimaldBExactDecimaldBExactDecimaldB
FL11.0000.0000.000−∞00.000−∞
FR00.000−∞11.0000.0000.000−∞
C00.000−∞00.000−∞11.0000.00
SL1/√20.707−3.0100.000−∞00.000−∞
SR00.000−∞1/√20.707−3.0100.000−∞
BL1/√20.707−3.0100.000−∞00.000−∞
BR00.000−∞1/√20.707−3.0100.000−∞
Top1/√30.577−4.771/√30.577−4.771/√30.577−4.77
HFL1/√20.707−3.0100.000−∞00.000−∞
HFC00.000−∞00.000−∞1/√20.707−3.01
HFR00.000−∞1/√20.707−3.0100.000−∞
HBL1/20.500−6.0200.000−∞00.000−∞
HBR00.000−∞1/20.500−6.0200.000−∞

To 4.x

Input ChannelsLRSLSR
 ExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldB
FL11.0000.0000.000−∞00.000−∞00.000−∞
FR00.000−∞11.0000.0000.000−∞00.000−∞
C1/√20.707−3.011/√20.707−3.0100.000−∞00.000−∞
SL00.000−∞00.000−∞11.0000.0000.000−∞
SR00.000−∞00.000−∞00.000−∞11.0000.00
BL00.000−∞00.000−∞11.0000.0000.000−∞
BR00.000−∞00.000−∞00.000−∞11.0000.00
Top1/√40.500−6.021/√40.500−6.021/√40.500−6.021/√40.500−6.02
HFL1/√20.707−3.0100.000−∞00.000−∞00.000−∞
HFC1/20.500−6.021/20.500−6.0200.000−∞00.000−∞
HFR00.000−∞1/√20.707−3.0100.000−∞00.000−∞
HBL00.000−∞00.000−∞1/√20.707−3.0100.000−∞
HBR00.000−∞00.000−∞00.000−∞1/√20.707−3.01

To 5.x

Input ChannelsLRCSLSR
 ExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldB
FL11.0000.0000.000−∞00.000−∞00.000−∞00.000−∞
FR00.000−∞11.0000.0000.000−∞00.000−∞00.000−∞
C00.000−∞00.000−∞11.0000.0000.000−∞00.000−∞
SL00.000−∞00.000−∞00.000−∞11.0000.0000.000−∞
SR00.000−∞00.000−∞00.000−∞00.000−∞11.0000.00
BL00.000−∞00.000−∞00.000−∞11.0000.0000.000−∞
BR00.000−∞00.000−∞00.000−∞00.000−∞11.0000.00
Top1/√50.447−6.991/√50.447−6.991/√50.447−6.991/√50.447−6.991/√50.447−6.99
HFL1/√20.707−3.0100.000−∞00.000−∞00.000−∞00.000−∞
HFC00.000−∞00.000−∞1/√20.707−3.0100.000−∞00.000−∞
HFR00.000−∞1/√20.707−3.0100.000−∞00.000−∞00.000−∞
HBL00.000−∞00.000−∞00.000−∞1/√20.707−3.0100.000−∞
HBR00.000−∞00.000−∞00.000−∞00.000−∞1/√20.707−3.01

To 6.x

Input ChannelsLRSLSRBLBR
 ExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldB
FL11.0000.0000.000−∞00.000−∞00.000−∞00.000−∞00.000−∞
FR00.000−∞11.0000.0000.000−∞00.000−∞00.000−∞00.000−∞
C1/√20.707−3.011/√20.707−3.0100.000−∞00.000−∞00.000−∞00.000−∞
SL00.000−∞00.000−∞11.0000.0000.000−∞00.000−∞00.000−∞
SR00.000−∞00.000−∞00.000−∞11.0000.0000.000−∞00.000−∞
BL00.000−∞00.000−∞00.000−∞00.000−∞11.0000.0000.000−∞
BR00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞11.0000.00
Top1/√60.408−7.781/√60.408−7.781/√60.408−7.781/√60.408−7.781/√60.408−7.781/√60.408−7.78
HFL1/√20.707−3.0100.000−∞00.000−∞00.000−∞00.000−∞00.000−∞
HFC1/20.500−6.021/20.500−6.0200.000−∞00.000−∞00.000−∞00.000−∞
HFR00.000−∞1/√20.707−3.0100.000−∞00.000−∞00.000−∞00.000−∞
HBL00.000−∞00.000−∞00.000−∞00.000−∞1/√20.707−3.0100.000−∞
HBR00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞1/√20.707−3.01

To 7.x

Input ChannelsLRCSLSRBLBR
 ExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldBExactDecimaldB
FL11.0000.0000.000−∞00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞
FR00.000−∞11.0000.0000.000−∞00.000−∞00.000−∞00.000−∞00.000−∞
C00.000−∞00.000−∞11.0000.0000.000−∞00.000−∞00.000−∞00.000−∞
SL00.000−∞00.000−∞00.000−∞11.0000.0000.000−∞00.000−∞00.000−∞
SR00.000−∞00.000−∞00.000−∞00.000−∞11.0000.0000.000−∞00.000−∞
BL00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞11.0000.0000.000−∞
BR00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞11.0000.00
Top1/√70.378−8.451/√70.378−8.451/√70.378−8.451/√70.378−8.451/√70.378−8.451/√70.378−8.451/√70.378−8.45
HFL1/√20.707−3.0100.000−∞00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞
HFC00.000−∞00.000−∞1/√20.707−3.0100.000−∞00.000−∞00.000−∞00.000−∞
HFR00.000−∞1/√20.707−3.0100.000−∞00.000−∞00.000−∞00.000−∞00.000−∞
HBL00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞1/√20.707−3.0100.000−∞
HBR00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞00.000−∞1/√20.707−3.01

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