[alsa-devel] What are subdevices?
Hi!
I tried this question in the alsa-users mailing list but it doesn't appear to be much active. So I ask here.
I'm facing problems with my system, so decided to learn ALSA to see what's the problem.
My first question -- what's a device and a sub device?
A device seems like the output streams the sound card supports. Like HDMI, DP, analog etc...
So what's a subdevice? Is this related to multichannel? Does it designate physical ports on the card?
Thanks.
dE wrote:
A device seems like the output streams the sound card supports. Like HDMI, DP, analog etc...
So what's a subdevice?
A subdevice is an output streams the sound card supports.
Typically, a device has multiple subdevices if the card supports hardware mixing; all the subdevices end up at the same physical output.
Regards, Clemens
On 10/26/14 14:41, Clemens Ladisch wrote:
dE wrote:
A device seems like the output streams the sound card supports. Like HDMI, DP, analog etc...
So what's a subdevice?
A subdevice is an output streams the sound card supports.
Typically, a device has multiple subdevices if the card supports hardware mixing; all the subdevices end up at the same physical output.
Regards, Clemens
Ok, so a device list is a list of different streams the card can supports simultaneously and they'll be output via different channels without mixing.
Thanks for clarifying this.
But, typically cards have a single analog device but support multichannel output. So how does this work at the software level? If ALSA can't send multiple streams of audio to one device, then how does ALSA send separate output to different channels of the device?
Is the PCM sent to the sound card codified? Is this the same way how stereo work?
On 10/26/14 15:27, dE wrote:
On 10/26/14 14:41, Clemens Ladisch wrote:
dE wrote:
A device seems like the output streams the sound card supports. Like HDMI, DP, analog etc...
So what's a subdevice?
A subdevice is an output streams the sound card supports.
Typically, a device has multiple subdevices if the card supports hardware mixing; all the subdevices end up at the same physical output.
Regards, Clemens
Ok, so a device list is a list of different streams the card can supports simultaneously and they'll be output via different channels without mixing.
Thanks for clarifying this.
But, typically cards have a single analog device but support multichannel output. So how does this work at the software level? If ALSA can't send multiple streams of audio to one device, then how does ALSA send separate output to different channels of the device?
Is the PCM sent to the sound card codified? Is this the same way how stereo work?
No one knows?
dE wrote:
typically cards have a single analog device but support multichannel output. So how does this work at the software level? If ALSA can't send multiple streams of audio to one device, then how does ALSA send separate output to different channels of the device?
The channels are not separate. For a stereo devices, the samples are arranged like LRLRLRLRLR...; for more channels, there are more interleaved values: 123456123456123456123456...
Regards, Clemens
On 10/28/14 01:16, Clemens Ladisch wrote:
dE wrote:
typically cards have a single analog device but support multichannel output. So how does this work at the software level? If ALSA can't send multiple streams of audio to one device, then how does ALSA send separate output to different channels of the device?
The channels are not separate. For a stereo devices, the samples are arranged like LRLRLRLRLR...; for more channels, there are more interleaved values: 123456123456123456123456...
Regards, Clemens _______________________________________________ Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
So it's with the encoding of the PCM.
Thank you so much for the response! I'll blog about this in my ALSA doc.
participants (2)
-
Clemens Ladisch -
dE