[MPlayer-dev-eng] Re: [PATCH] af_ambisonic

Nicolas George nicolas.george at ens.fr
Sat Apr 21 18:33:05 CEST 2007

Le duodi 2 floréal, an CCXV, Nico Sabbi a écrit :
> 1) mplayer -channels 6 -af amb=sources=5.1ac3 -ao pcm:file=sound.wav
> 2) mplayer -af amb=sinks=2 sound.wav

I am not totally sure, but I believe that is not what ambisonic is made for.
As fare as I understand, you will need ambisonic if you have a 5.1 source,
5.1 speakers, but want to encode at a lower bitrate. In that case, you:

1a. Downmix from 5.1 to 3 channels with ambisonic.

1b. Encode at a bitrate adapted to 3 channels audio.

2a. Decode.

2b. Upmix from 3 channels to 5.1 with ambisonic.

2c. Listen to the result on 5.1 speakers.

And the result is supposed to be almost as good as the original, although I
do not know how they do it[1].

If your goal is only to listen on 2 channels speakers, I do not think that
ambisonic would bring you anything.

I hope that Sebastian Olter will correct me if I am wrong. And that his
patch will be accepted if I am right, because it is a very interesting

1: In fact, I believe I have some understanding. For all that "stereo" means
"three dimensional", stereo 2 channels sound is in fact 1-dimensional, and
5.1 sound is 2-dimensional: you can have sound that pans from the left to
the right, from behind to the front, but not from the floor to the ceiling.
And to define a plane, there is only need for 3 points.


  Nicolas George
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