PCM substream

PCM substream

[arun kumar]

Hi All,


>From the last couple of days, I have been trying to understand the Linux
Alsa Subsystem.I have read the Alsa Driver API and Application API's. But I
could not understand the concept of PCM substreams, Could you please give
me some pointers to get a good understanding on the PCM substream.


regards,
Arun.

Re: PCM substream

[Clemens Ladisch]

arun kumar wrote:
> From the last couple of days, I have been trying to understand the Linux
> Alsa Subsystem.I have read the Alsa Driver API and Application API's. But I
> could not understand the concept of PCM substreams,

A PCM stream has one or more substreams.  Multiple substreams are used when
the hardware can mix them together for one output.  This was used in old
wavetable sound cards; nowadays, you almost always have one substream.


Regards,
Clemens

Re: PCM substream

[arun kumar]

Hi Clemens,

Thanks for the reply.So, if any application tries to open more than one
substream will it get the error? or alsa subsystem gives it one more
substream and helps in mixing of substreams considering my hardware has
only support for one substream.

regards,
Arun.
On Thu, Aug 9, 2012 at 6:19 PM, Clemens Ladisch <clemens@ladisch.de> wrote:

> arun kumar wrote:
> > From the last couple of days, I have been trying to understand the Linux
> > Alsa Subsystem.I have read the Alsa Driver API and Application API's.
> But I
> > could not understand the concept of PCM substreams,
>
> A PCM stream has one or more substreams.  Multiple substreams are used when
> the hardware can mix them together for one output.  This was used in old
> wavetable sound cards; nowadays, you almost always have one substream.
>
>
> Regards,
> Clemens
>

Re: PCM substream

[Clemens Ladisch]

(please don't top-post)

arun kumar wrote:
> So, if any application tries to open more than one substream will it
> get the error?

If there is no free substream available, the application will get an
error.

(If some mixing sound server like PulseAudio is used, this does not
matter.)


Regards,
Clemens

Re: PCM substream

[Raymond Yau]

2012-8-9 下午8:49 於 "Clemens Ladisch" <clemens@ladisch.de> 寫道：
>
> arun kumar wrote:
> > From the last couple of days, I have been trying to understand the Linux
> > Alsa Subsystem.I have read the Alsa Driver API and Application API's.
But I
> > could not understand the concept of PCM substreams,
>
> A PCM stream has one or more substreams.  Multiple substreams are used
when
> the hardware can mix them together for one output.  This was used in old
> wavetable sound cards; nowadays, you almost always have one substream.
>

There are some hda controllers support multi-stream capture and some hda
codecs have two or more adc which allow two applications using different mic

> List of CAPTURE Hardware Devices ****
card 0: Intel [HDA Intel], device 0: AD198x Analog [AD198x Analog]
  Subdevices: 3/3
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
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