LinuxQuestions.org - [SOLVED] Weird ALSA issue

I have a strange issu with ALSA : the default PCM works but doesn't seem to downmix 5.1 sounds properly. So a good part of 5.1 audio tracks is lost.
aplay tells me the device is supported all right :

Code:

bash-4.2$ aplay -L

null

    Discard all samples (playback) or generate zero samples (capture)

default:CARD=SB

    HDA ATI SB, ALC889A Analog

    Default Audio Device



(snip)



surround51:CARD=SB,DEV=0

    HDA ATI SB, ALC889A Analog

    5.1 Surround output to Front, Center, Rear and Subwoofer speakers

But, although aplay can play a 5.1 without downmix all right on the default PCM :

Code:

bash-4.2$ aplay Master51FemmeSqueletteDCP_24fps.wav

Lecture WAVE 'Master51FemmeSqueletteDCP_24fps.wav' : Signed 24 bit Little Endian in 3bytes, Fréquence 48000 Hz, 6 Canaux

It fails when I try to force the 5.1 PCM :

Code:

ash-4.2$ aplay -D surround51 Master51FemmeSqueletteDCP_24fps.wav

Lecture WAVE 'Master51FemmeSqueletteDCP_24fps.wav' : Signed 24 bit Little Endian in 3bytes, Fréquence 48000 Hz, 6 Canaux

aplay: set_params:1233: Ce format d'échantillonage n'est pas disponible

Available formats:

- S16_LE

- S32_LE

bash-4.2$

Why is the default accepting S24_3LE and not the surround51, I can't say, I can't find any information anywhere.

Never mind, I say to myself, let's configure the "surround51" PCM in /etc/asound.conf to use the "vdownmix" plugin (I have to compile it as it is not provided by Slackware, but that's not an issue), like this :

pcm.!surround51 {
type vdownmix
slave.pcm "default"
}

Fine, but "aplay -L" does not list the surround51 PCM anymore. And still fails to read the file :

Code:

bash-4.2$ aplay -D surround51 Master51FemmeSqueletteDCP_24fps.wav

Lecture WAVE 'Master51FemmeSqueletteDCP_24fps.wav' : Signed 24 bit Little Endian in 3bytes, Fréquence 48000 Hz, 6 Canaux

aplay: set_params:1233: Ce format d'échantillonage n'est pas disponible

Available formats:

- S16_LE

The default PCM still does not downmix properly.
If anyone that knows quite a bit more than me about Alsa can give me a hand or just point out where I am failing completely, I'd be very interested.