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Old 6th August 2013, 22:38   #1  |  Link
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Downmix to 2.1

What's a good strategy to downmix audio (mainly 5.1 Dolby(c)) to 2.1 ?
Specifically: what tool(s) ? And what target codec ?


Last edited by Guest; 6th August 2013 at 23:59. Reason: 12
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Old 7th August 2013, 09:07   #2  |  Link
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Posts: 6,011
Is not recommended downmix 5.1 to 2.1.

Don't mistake subwoofer with LFE channel.
An audio equipment 2.1 send to subwoofer all low audio frequencies from all channels, not only the LFE channel.
Also audio equipment 2.1, most the times, have only stereo input for that reason.

BTW, if you want do some test, you can load this avs script in BeHappy:
  NicAc3Source("full path to your ac3 5.1 file.ac3")
  flr = GetChannel(a, 1, 2)
  fcc = GetChannel(a, 3, 3)
  lrc = MixAudio(flr, fcc, 0.3694, 0.2612)
  blr = GetChannel(a, 5, 6)
  lrf = MixAudio(lrc, blr, 1.0, 0.3694)
  lfe = GetChannel(a, 4)
  MergeChannels(lrf, lfe)
and encode to AC3 at bitrate 256 or 192.

You need AviSynth, BeHapy, NicAudio.dll like decoder and Aften.exe like encoder.
BeHappy, AviSynth audio transcoder.
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Old 7th August 2013, 12:14   #3  |  Link
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@tebasuna51: thx for your answer, you seem to know what you're talking about !
I agree with your remarks, that's why my question was very general..
I'm looking for a "smart" downmix, not, for example, to map LFE 1:1 to a channel in the 2.1 result (which is what your script does ).
My equipment does have only stereo input, but I figured an added channel dedicated to LFs would make the signal "richer" when downmixed to stereo during playback..

I would be happy with a 5.1 AC3 minus surround (keeping just L,R,C+LFE), but I don't know how to do it. Extracting mono WAVs is easy, but encoding 3.0+LFE with Aften yields a broken AC3 file: a 40mn piece encoded by Aften has "varying length" () - up to 7h ! - in different players (including latest VLC) : yes ! Showed total length of the audio changes during playback (!!) which indicates a broken file.
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