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Old 07-27-2013, 07:55 AM   #1
rvdboom
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Registered: Jul 2007
Distribution: Slackware
Posts: 186

Rep: Reputation: 23
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.
 
Old 07-27-2013, 08:15 AM   #2
rvdboom
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Registered: Jul 2007
Distribution: Slackware
Posts: 186

Original Poster
Rep: Reputation: 23
Well, I seem to have found some docs that tells that some plugins indeed only support specific sound formats.

https://bbs.archlinux.org/viewtopic.php?id=163041

So I guess that's pretty clear.....
 
  


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