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Old Yesterday, 19:05   #1  |  Link
manolito
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AviSynth Downmix Scripts

This is a question for Tebasuna:

In AVStoDVD MrC uses downmix scripts from you. For downmixing 8ch audio to 6ch the script is this one:
Quote:
Function Dmix86(clip a)
{
flr = Getchannel(a, 1, 2, 3, 4)
blr = Getchannel(a, 5, 6)
slr = Getchannel(a, 7, 8)
sur = MixAudio(blr, slr, 1.0, 1.0)
return MergeChannels(flr,sur)
}
Now over at VideoHelp JuMe proposed a different script:

Quote:
The formula for 7.1 to 5.1 is a little more complicated:

Ls' = Ls + (-1,2 dB) ◊ Lrs + (-6,2 dB) ◊ Rrs
Rs' = Rs + (-1,2 dB) ◊ Rrs + (-6,2 dB) ◊ Lrs

In other words, surround back -channels are partially mixed together before they are combined with side surrounds. Iím a complete novice with Avisynth, so there is probably more sophisticated way of writing the script, but this is what Iíve been using:

Quote:
Function Dmix8to6(clip a)
{
front = Getchannel(a, 1, 2, 3, 4)
bl = Getchannel(a, 5)
br = Getchannel(a, 6)
sl = Getchannel(a, 7)
sr = Getchannel(a, 8)
bl_new = MixAudio(bl, br, 0.8710, 0.4898)
br_new = MixAudio(br, bl, 0.8710, 0.4898)
sl_final = MixAudio(sl, bl_new, 1.0, 1.0)
sr_final = MixAudio(sr, br_new, 1.0, 1.0)
return MergeChannels(front, sl_final, sr_final)
}
Any comments?
I cannot really judge this script because I do not have a surround setup for audio (I'm old school - Stereo Only)


Cheers
manolito
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Old Today, 00:31   #2  |  Link
tebasuna51
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Quote:
Originally Posted by manolito View Post
In AVStoDVD MrC uses downmix scripts from you. For downmixing 8ch audio to 6ch the script is this one:
That 'Function Dmix86' must be used with float audio samples and after the merged clip must be Normalized to avoid clips in MixAudio(blr, slr, 1.0, 1.0).

I recommend the script used in BeHappy or MeGUI with the sur like this:

sur = MixAudio(blr, slr, 1.0, 1.0).SoftClipperFromAudX(0.0)

Now we don't need Normalize and the four first channels preserve the proper volume.

Quote:
Now over at VideoHelp JuMe proposed a different script:
Any comments?
The conversion between formula and avs script is correct (remember float samples and normalize after with volume problems).

Any user can do the desired mix but I can't recommend that formula at all.
For what, to obtain surround channels in 5.1, you need mix left and right channels?
The Ls channel is a mix of Lss and Lsr, put Rsr is a mistake:
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