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Old 03-19-2006, 12:34 PM   #1
gavinln
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Registered: Mar 2006
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Enable AC3 passthrough for Audigy 2 value


How do I enable the ac3 passthrough so that my external decoder indicates "Dolby Digital" sound and I get surround sound?

I have a Creative Labs SB0400 Audigy2 Value card installed on a Fedora Core 4 machine and it shows up correctly using lspci as below
Code:
#/sbin/lspci | grep audio
02:00.0 Multimedia audio controller: Creative Labs SB0400 Audigy2 Value
My modprobe.conf uses the emu101k driver as shown below
Code:
# ALSA portion
alias snd-card-0 snd-emu10k1
options snd-card-0 index=0
install snd-emu10k1 /sbin/modprobe --ignore-install snd-emu10k1 && /usr/sbin/alsactl restore >/dev/null 2>&1 || :
remove snd-emu10k1 { /usr/sbin/alsactl store >/dev/null 2>&1 || : ; }; /sbin/modprobe -r --ignore-remove snd-emu10k1
The audio devices for my sound card are shown below
Code:
# cat /proc/asound/devices | grep audio
 19: [0- 3]: digital audio playback
 18: [0- 2]: digital audio playback
 26: [0- 2]: digital audio capture
 25: [0- 1]: digital audio capture
 16: [0- 0]: digital audio playback
 24: [0- 0]: digital audio capture
The audio devices can also be displayed using aplay -l as below
Code:
# aplay -l | grep Audigy
card 0: Audigy2 [Audigy 2 Value [SB0400]], device 0: emu10k1 [ADC Capture/Standard PCM Playback]
card 0: Audigy2 [Audigy 2 Value [SB0400]], device 2: emu10k1 efx [Multichannel Capture/PT Playback]
card 0: Audigy2 [Audigy 2 Value [SB0400]], device 3: emu10k1 [Multichannel Playback]
What device should I use to play audio? And If I want to play AC3 using SPDIF (Coaxial) through an external Dolby Digital Decoder what device do I use?

Using device 0, I am able to play sounds using SPDIF.
Code:
$ aplay -D hw:0,0  /usr/share/sounds/KDE_Startup.wav 
Playing WAVE '/usr/share/sounds/KDE_Startup.wav' : Signed 16 bit Little Endian, Rate 22050 Hz, Mono
None of the others devices work though with different errors
Code:
$ aplay -D hw:0,1  /usr/share/sounds/KDE_Startup.wav 
aplay: main:542: audio open error: No such file or directory
$ aplay -D hw:0,2  /usr/share/sounds/KDE_Startup.wav 
aplay: main:542: audio open error: No such device
$ aplay -D hw:0,3  /usr/share/sounds/KDE_Startup.wav 
Playing WAVE '/usr/share/sounds/KDE_Startup.wav' : Signed 16 bit Little Endian, Rate 22050 Hz, Mono
aplay: set_params:889: Access type not available
If I use a DVD with AC3 sound with the following command it works well and I get two channel sound
Code:
$ mplayer -ao alsa:device=hw=0.0 dvd://1
Mplayer shows the following alsa output
Code:
alsa-init: 1 soundcard found, using: hw:0,0
alsa: 48000 Hz/2 channels/4 bpf/65536 bytes buffer/Signed 16 bit Little Endian
AO: [alsa] 48000Hz 2ch s16le (2 bps)
If I then enable ac3 passthrough I get a clicking sound on my speakers when using the following command
Code:
$ mplayer -ao alsa:device=hw=0.0  -ac hwac3 dvd://1
The mplayer alsa output is
Code:
alsa-init: 1 soundcard found, using: hw:0,0
alsa: 48000 Hz/2 channels/4 bpf/65536 bytes buffer/Signed 16 bit Little Endian
AO: [alsa] 48000Hz 2ch ac3 (1 bps)
If I use the "-ac hwac3" flag with other devices "hw=0.1 or hw=0.2 or hw=0.3" I do not get any sound.

How do I enable the ac3 passthrough so that my external decoder indicates "Dolby Digital" sound and I get surround sound?
 
Old 05-02-2006, 07:19 PM   #2
mrchaos
Member
 
Registered: Mar 2005
Location: USA
Distribution: Slackware current, Fedora Core 5, SuSE 10.1 OSS
Posts: 298

Rep: Reputation: 30
in case you're still wondering...

try
Code:
aplay -D plughw:0,3  /usr/share/sounds/KDE_Startup.wav
in your command line, adding the term "plug" into the code allows for the audigy 2 value to output through spdif to coax...

*edit*
I imagine that substituting
Code:
mplayer -ao alsa:device=plughw=0.0  -ac hwac3 dvd://1
may also answer your question, but I do not have mplayer in front of me to test this

Last edited by mrchaos; 05-02-2006 at 07:23 PM.
 
  


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