[MPlayer-dev-eng] surround sound documentation

[Jan Knutar]

On Sunday 21 August 2005 01:54, Corey Hickey wrote:

> I have the hardware but not the audio equipment. I just spent a few
> minutes plugging a pair of headphones into various audio jacks and
> mplayer's surround support seems to work ok. With alsa I can just:
> 
> 1. mplayer -channels 6 -ao alsa

I'll confirm this...

I have a cheapo $10 sound board but no speakers (not even cheapo
ones) to match. mplayer -channels 6 -ao alsa seems to work ok, tested
with same method of plugging headphones into various audio jacks :-)

> 2. run alsamixer and play around with the various controls.

Yes, I seem to have to switch digital off, while playing 6 channels
the "Master volume" and "PCM" controls change meaning and become
"Front" and "Rear". Oddly enough it seems MPlayer's own audio control
somehow figures this out, but it's kind of difficult to confirm with frantic
replugging of headphones...

In general it would seem that the mixer settings can be important,
and their meaning seems to change from board to board and even
between different modes of playback, it would seem. I am guessing
this is because there are about 100 different actual boards made
that contain the exact same hardware, but with different circuit pathways
which makes everything routed a bit differently, electrically,  and no easy
way to distinguish between all these numerous variants.

As a curiosity, my previous sound board, a Creative something or other,
named ens1371 in ALSA, would in some hardware configurations be capable
of 6 channel playback through changing mixer settings to reconfigure the audio
jacks from mic and line-in to rear and LFE/Center, but mine was not electrically
wired to do so. Amusingly, the card was not sold with "3D Stereo" enhancment
advertised, but the hardware was capable of it, and ALSA found the setting for it,
and it even worked.

My current board, "C-Media Electronics Inc CM8738", was marketed as having
that same "3D Stereo Enhancement" (I guess similar to extrastereo in -af), but
the actual board seems unaware of this. Maybe the windows drivers implements
it in software :)