26 Oct
2009
26 Oct
'09
10:19 a.m.
Hi folks.
On my quest to get more then two channels from Alsa out to the 9632
I stepped over this:
I figured that there is just a pcm0p under /proc/asound/card0.
Shouldn't there be pcm0p...pcm7p reflecting the 8 Alsa stereo channels on
the HDSP?
What am I mixing up here?
THX for your patience.
\Klaus
26 Oct
26 Oct
11:23 a.m.
Hi Klaus,
the ALSA hardware device is just a single 18 channel (or whatever number
of channels you have) device. The ALSA plughw-device does some mapping,
which allows playback of different channel count on your multichannel
card. The signal routing can be controlled in the ALSA settings (see
'route_policy').
To simultaneously access the single device with different applications
you should define a 'dmix' software device. I am not an expert on dmix
settings, it is described on
http://www.alsa-project.org/main/index.php/Asoundrc
However, I did not find a documentation on how to setup multiple stereo
devices with different output channels.
All this is no problem at all with jack, simply connect any client to
the channels you want (or route from client to client). Most
applications support jack, so it should not be a problem. No GUI is
needed (for headless setups).
--
Giso
Klaus Schulz wrote:
Hi folks.
On my quest to get more then two channels from Alsa out to the 9632
I stepped over this:
I figured that there is just a pcm0p under /proc/asound/card0.
Shouldn't there be pcm0p...pcm7p reflecting the 8 Alsa stereo channels
on the HDSP?
What am I mixing up here?
12:30 p.m.
THX Giso.
I already looked into the .asoundrc Wiki. I couldn't really make sense of
it.
I 'll checkout Jack. I just wanted to avoid another layer in the chain. I
also didn't want to mix things
on the PC side. I didn't expect difficulties to send three stereo streams
straight to the device mixer.
For now the easiset solution I figured out would be to play a multichannel
wav:
sox -M 1.wav 2.wav 3.wav -t wavpcm - | aplay -D plughw:0,0 -f cd
Cheers
On Mon, Oct 26, 2009 at 3:23 PM, Giso Grimm <gg3137(a)vegri.net> wrote:
Hi Klaus,
the ALSA hardware device is just a single 18 channel (or whatever number
of channels you have) device. The ALSA plughw-device does some mapping,
which allows playback of different channel count on your multichannel
card. The signal routing can be controlled in the ALSA settings (see
'route_policy').
To simultaneously access the single device with different applications
you should define a 'dmix' software device. I am not an expert on dmix
settings, it is described on
http://www.alsa-project.org/main/index.php/Asoundrc
However, I did not find a documentation on how to setup multiple stereo
devices with different output channels.
All this is no problem at all with jack, simply connect any client to
the channels you want (or route from client to client). Most
applications support jack, so it should not be a problem. No GUI is
needed (for headless setups).
--
Giso
Klaus Schulz wrote:
Hi folks.
On my quest to get more then two channels from Alsa out to the 9632
I stepped over this:
I figured that there is just a pcm0p under /proc/asound/card0.
Shouldn't there be pcm0p...pcm7p reflecting the 8 Alsa stereo channels
on the HDSP?
What am I mixing up here?
1:32 p.m.
On Mon, Oct 26, 2009 at 11:30 AM, Klaus Schulz <kls.schlz(a)googlemail.com> wrote:
THX Giso.
I already looked into the .asoundrc Wiki. I couldn't really make sense of
it.
I 'll checkout Jack. I just wanted to avoid another layer in the chain. I
also didn't want to mix things
on the PC side. I didn't expect difficulties to send three stereo streams
straight to the device mixer.
then you haven't understood ALSA at all.
if you want multiple apps to send independent streams to a device, you
have 3 choices:
1) use dmix
2) use asoundrc to set up pseudo-devices mapped to distinct
channels, and have each app use a different pseudo-device
3) use a sound server that knows what its doing (JACK being one example)
if you want a single app to send independent streams to a device, then
the app has to know what its doing.
its not any simpler, or more complex, than that.
3:32 p.m.
On Mon, Oct 26, 2009 at 5:32 PM, Paul Davis <paul(a)linuxaudiosystems.com>wrote;wrote:
On Mon, Oct 26, 2009 at 11:30 AM, Klaus Schulz
<kls.schlz(a)googlemail.com>
wrote:
That's possible. (Don't expect me I to startup discussions about quality
of
Alsa documentation etc., Alsa I regard as designer territory - I am just a
poor user.)
THX Giso.
I already looked into the .asoundrc Wiki. I couldn't really make sense
of
it.
I 'll checkout Jack. I just wanted to avoid another layer in the chain. I
also didn't want to mix things
on the PC side. I didn't expect difficulties to send three stereo streams
straight to the device mixer.
then you haven't understood ALSA at all.
if you want multiple apps to send independent streams
to a device, you
have 3 choices:
1) use dmix
2) use asoundrc to set up pseudo-devices mapped to distinct
channels, and have each app use a different pseudo-device
3) use a sound server that knows what its doing (JACK being one example)
Paul. I know all that. I am just lacking the knowledge of how to link the
output stream to a dedicated channel.
if you want a single app to send independent streams
to a device, then
the app has to know what its doing.
its not any simpler, or more complex, than that.
Pretty simple - You IMO still did not answer the question. How about an
example for 2) ?
For now the only way to sent a stream to e.g. the out3/4 of HDSPmixer
without going for 1)2)3) has been a multichannel wav.
Cheers
3:41 p.m.
On Mon, Oct 26, 2009 at 2:32 PM, Klaus Schulz <kls.schlz(a)googlemail.com> wrote:
Pretty simple - You IMO still did not answer the
question. How about an
example for 2) ?
For now the only way to sent a stream to e.g. the out3/4 of HDSPmixer
without going for 1)2)3) has been a multichannel wav.
you've opened a device that has N channels. you have to send it N
channels of data. there is no way around this. ALSA has no API for
"write to channel 1", it only has "write N frames of audio". in fact,
i don't know of any audio API that has such a mechanism.
if you don't want to do that, then you need to configure some
pseudo-devices that have the number of channels you want, and that use
the route plugin to map the pseudo-device's channels to the "real"
channels in the hw device. then open that device with your
application.
3:57 p.m.
Paul Davis wrote:
if you don't want to do that, then you need to
configure some
pseudo-devices that have the number of channels you want, and that use
the route plugin to map the pseudo-device's channels to the "real"
channels in the hw device. then open that device with your
application.
Interesting!
Oh by the way, is there any overhead (CPU, latency, etc) in this
approach using the route plugin?
thnks!
5553
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4 participants
participants (4)
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Giso Grimm -
Klaus Schulz -
Paul Davis -
Peter Plessas