A better 5.1 -> 2.0 Channel mapping

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A better 5.1 -> 2.0 Channel mapping

Postby kokoko3k on Fri Jun 12, 2009 11:56 am

Do you own a 2.0 speaker system and want to know how to correct map a 5.1 channels source on it?

First, i suggest you to download this useful Video,
it will play single channels individually providing a visual feedback
http://wpage.unina.it/aorefice/xt7playe ... C3Test.avi

If you didn't touch any of the mplayer/xt7-player settings, probably you'll ear all the channels, but the LFE one (the one used for lower frequencies).
Apart from the missing channel, one major problem still exists, the volume balancing between them.
Have you ever tried to watch a 5.1 DVD on your 2.0 speaker system?
You may have noticed that characters voices are often at very low volume level, expecially compared to background effects/music, this is because default mplayer settings configure all the channels to the same volume and, considering that often the soundtrack (as well as background effects) is replicated to front and rear channels, it's clear that voices will 'suffer', because they are usually played through the center channel/speaker only.

As usual, mplayer comes with options and filters to correct 'the issue', they are:
-vf pan filter (which allows you to mix different channels and specify a volume for them)
-channels option (which is necessary for pan filter to work properly)

The meaning is a little tricky, i'll try to explain:
pan=2:0.5:0:0:0.5:0.5:0:0:0.5:1:1:0.5:0.5
The first number: 2 is the number of output channels we'll use
Next, for each Input channel, we'll specify the volume at which it will be mixed into the output one;
"1" means no volume changes
"0.5" means halving the volume
"0" means no mix.
(other values are allowed, of course)

The order is:
Say the input channel is :IC
and the output channel is: OC, we'll have:
pan=2 :
OC0 IC0 : OC1 IC1 : OC0 IC2 : OC1 IC3 : OC0 IC4 : OC1 IC5 :
OC0 IC0 : OC1 IC1 : OC0 IC2 : OC1 IC3 : OC0 IC4 : OC1 IC5

It seems quite complicated, isn't?
Now the fun part, Xt7-player configuration:
Open general options window and select Audio tab,
Check and set Output Channels to 6 - Full 5.1
Image

Close the General options window and open the Chains one.
Drag a Custom filter in the AudioChain,
Image

click on the filter and check (enable) a free slot, write in it:
Code: Select all
pan=2:0.5:0:0:0.5:0.5:0:0:0.5:1:1:0.5:0.5

Image

Save/use and try Ac3Test.avi again, you not only will notice that LFE channel is played correctly now, but also that the center channel is more 'present'.

You can play with pan values of course;
as a general rule, lowering 0.5 values will help you to hear speakings.
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kokoko3k
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