* What are subdevices?
@ 2014-10-26 8:14 dE
2014-10-26 9:11 ` Clemens Ladisch
0 siblings, 1 reply; 6+ messages in thread
From: dE @ 2014-10-26 8:14 UTC (permalink / raw)
To: Alsa-devel
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.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: What are subdevices?
2014-10-26 8:14 What are subdevices? dE
@ 2014-10-26 9:11 ` Clemens Ladisch
2014-10-26 9:57 ` dE
0 siblings, 1 reply; 6+ messages in thread
From: Clemens Ladisch @ 2014-10-26 9:11 UTC (permalink / raw)
To: dE, Alsa-devel
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: What are subdevices?
2014-10-26 9:11 ` Clemens Ladisch
@ 2014-10-26 9:57 ` dE
2014-10-27 18:02 ` dE
2014-10-27 19:46 ` Clemens Ladisch
0 siblings, 2 replies; 6+ messages in thread
From: dE @ 2014-10-26 9:57 UTC (permalink / raw)
To: Alsa-devel
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?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: What are subdevices?
2014-10-26 9:57 ` dE
@ 2014-10-27 18:02 ` dE
2014-10-27 19:46 ` Clemens Ladisch
1 sibling, 0 replies; 6+ messages in thread
From: dE @ 2014-10-27 18:02 UTC (permalink / raw)
To: Alsa-devel
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?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: What are subdevices?
2014-10-26 9:57 ` dE
2014-10-27 18:02 ` dE
@ 2014-10-27 19:46 ` Clemens Ladisch
2014-10-28 3:17 ` dE
1 sibling, 1 reply; 6+ messages in thread
From: Clemens Ladisch @ 2014-10-27 19:46 UTC (permalink / raw)
To: alsa-devel
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: What are subdevices?
2014-10-27 19:46 ` Clemens Ladisch
@ 2014-10-28 3:17 ` dE
0 siblings, 0 replies; 6+ messages in thread
From: dE @ 2014-10-28 3:17 UTC (permalink / raw)
To: Alsa-devel
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.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2014-10-28 3:17 UTC | newest]
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-- links below jump to the message on this page --
2014-10-26 8:14 What are subdevices? dE
2014-10-26 9:11 ` Clemens Ladisch
2014-10-26 9:57 ` dE
2014-10-27 18:02 ` dE
2014-10-27 19:46 ` Clemens Ladisch
2014-10-28 3:17 ` dE
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