[MPlayer-dev-eng] [PATCH] Automatic downmix

[Tobias Diedrich]

A bit late into the discussion, but...

Clément Bœsch wrote:
>  /*                FL       FR       RL       RR          FC          LF         AL      AR */
>  [3] = "pan=2:" "0.6:0:" "0:0.6:"                     "0.4:0.4",
>  [4] = "pan=2:" "0.6:0:" "0:0.6:" "0.4:0:"  "0:0.4",
>  [5] = "pan=2:" "0.5:0:" "0:0.5:" "0.2:0:"  "0:0.2:"  "0.3:0.3",
>  [6] = "pan=2:" "0.4:0:" "0:0.4:" "0.2:0:"  "0:0.2:"  "0.3:0.3:"   "0.1:0.1",
>  [7] = "pan=2:" "0.4:0:" "0:0.4:" "0.2:0:"  "0:0.2:"  "0.3:0.3:"              "0.1:0:" "0:0.1",
>  [8] = "pan=2:" "0.4:0:" "0:0.4:" "0.15:0:" "0:0.15:" "0.25:0.25:" "0.1:0.1:" "0.1:0:" "0:0.1",

I was wondering how you decided on the coefficents?
Apart from 'Everthing should add up to 1', some look rather
arbitrary.
For example I'd expect center and low frequency effects to have the
same coefficients.
It's also inconsistent, because for 6&7 FC/LF is 3, while for 8
channels FC/LF is 2.5...

Googling a bit turns up
http://forum.doom9.org/archive/index.php/t-57170.html
and
http://forum.doom9.org/showthread.php?s=&threadid=27936
and
http://www.atsc.org/cms/standards/a_52b.pdf

I think optionally using a Pro Logic matrix would make some sense
because some people may have a pro logic surround amplifier
connected to the stereo output.

For example:

Lt = 1.0*L + 0.707*C + 0.707*LFE - 0.8165*Ls - 0.5774*Rs
Rt = 1.0*R + 0.707*C + 0.707*LFE + 0.5774*Ls + 0.8165*Rs

And with downscaling:

Lt = .2626*L + .1856*C + .1856*LFE - .2144*Ls - .1516*Rs
Rt = .2626*R + .1856*C + .1856*LFE + .1516*Ls + .2144*Ls

-- 
Tobias						PGP: http://8ef7ddba.uguu.de