ALSA mixing capability

ALSA mixing capability

[Adam Tla/lka]

Welcome

I'm using ALSA 1.0.0rc2 on snd_intel8x0 and .asoundrc:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pcm.mix {
        type dmix
        ipc_key 321456  # any unique value
        ipc_key_add_uid true
        slave {
                pcm "hw:0,0"
                periods 0
                period_time 0
                period_size 1024  # must be power of 2
                buffer_size 4096  # ditto
        }
        bindings {
                0 0
                1 1
        }
}
ctl.mix { type hw card 0 }
pcm.dsp0 { type plug slave.pcm "mix" }
ctl.mixer0 { type hw card 0 }
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

My problem:

when using wavplay with OSS ALSA emulation playing 22050 and 11025 Hz 
.wav files works OK
but with AOSS lib using pcm.dsp0 defined above I can't play 11025 Hz 
.wav file:

$ aoss wavplay lburn2.wav
Pathname:       lburn2.wav
Device:         /dev/dsp
Sampling Rate:  11025 Hz
Mode:           Mono
Samples:        5999
Bits:           8

Unable to set audio sampling rate

but 22050 HZ .wav is played correctly.

So my question is how properly compose .asoundrc file so we could mix 
all sound sources which use ALSA natively
through -Dmix virtual device and OSS apps routed through AOSS lib? Is 
this possible? Is this explained somewhere?

Next case is a possibility to create a  virtual mixer so ctl.mix 
virtually sets level of particular source before mixing
it with others sources so playind applications could set volumen of only 
his source. Is that possible?

I thing that solution should be a snd kernel module which does this jobs 
(mixing and correcly setting volume level independently
for all apps, using hardware mixing if possible and software if not, DMA 
mapping etc.) which lays  below  OSS pcm emulation
module and pcm0p device and above hardware so no configuration changes 
in all apps are needed.
If it will working as a kernel high priority thread then some latency 
problems will gone too.

Regards

-- 
Adam Tla/lka      mailto:atlka@pg.gda.pl    ^v^ ^v^ ^v^
Computer Center,  Technical University of Gdansk, Poland
PGP public key:   finger atlka@sunrise.pg.gda.pl



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Re: ALSA mixing capability

[Jaroslav Kysela]

On Thu, 11 Dec 2003, Adam Tla/lka wrote:

> Welcome
> 
> I'm using ALSA 1.0.0rc2 on snd_intel8x0 and .asoundrc:
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> pcm.mix {
>         type dmix
>         ipc_key 321456  # any unique value
>         ipc_key_add_uid true
>         slave {
>                 pcm "hw:0,0"
>                 periods 0
>                 period_time 0
>                 period_size 1024  # must be power of 2
>                 buffer_size 4096  # ditto
>         }
>         bindings {
>                 0 0
>                 1 1
>         }
> }
> ctl.mix { type hw card 0 }
> pcm.dsp0 { type plug slave.pcm "mix" }
> ctl.mixer0 { type hw card 0 }
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> My problem:
> 
> when using wavplay with OSS ALSA emulation playing 22050 and 11025 Hz 
> .wav files works OK
> but with AOSS lib using pcm.dsp0 defined above I can't play 11025 Hz 
> .wav file:
> 
> $ aoss wavplay lburn2.wav
> Pathname:       lburn2.wav
> Device:         /dev/dsp
> Sampling Rate:  11025 Hz
> Mode:           Mono
> Samples:        5999
> Bits:           8
> 
> Unable to set audio sampling rate
> 
> but 22050 HZ .wav is played correctly.
> 
> So my question is how properly compose .asoundrc file so we could mix 
> all sound sources which use ALSA natively
> through -Dmix virtual device and OSS apps routed through AOSS lib? Is 
> this possible? Is this explained somewhere?

If you use mostly 44.1kHz material (or multiple of this rate), then 
explicitly set the 44.1kHz rate in pcm.dmix section (rate 44100). Note
that your hardware must support this rate.

Anyway, it seems like a bug.

> Next case is a possibility to create a  virtual mixer so ctl.mix 
> virtually sets level of particular source before mixing
> it with others sources so playind applications could set volumen of only 
> his source. Is that possible?

I know about this problem and it will be fixed one day.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs


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