[LAU] ALSA: Using a plugin only for capture

Paul Davis paul at linuxaudiosystems.com
Tue Dec 6 23:57:05 UTC 2011


On Tue, Dec 6, 2011 at 6:46 PM, Fons Adriaensen <fons at linuxaudio.org> wrote:
> On Tue, Dec 06, 2011 at 06:27:23PM -0500, Paul Davis wrote:
>> On Tue, Dec 6, 2011 at 5:43 PM, Fons Adriaensen <fons at linuxaudio.org> wrote:
>>
>> > So, are you telling us that ALSA inserts the plugin in both
>> > the capture and playback paths ? That would be absolutely
>> > braindead.
>>
>> doesn't work that way at all.
>>
>> the app opens "plughw:ladspa" (for example) for playback. presto: the
>> ladspa plugin is applied to the playback stream.
>> the app opens "hw:0" (for example) for capture. no plugin processing
>> on the capture stream.
>> the app opens "plughw:ladspa" (for example) for capture. presto: the
>> ladspa plugin is applied to the capture stream.
>
> And what if the app opens the device for capture and playback ?

it will open two streams, and the processing on each one depends on
the device name it uses to open each stream.

> Isn't the whole 'plug' system meant to be transparent to apps,
> so an app can just use 'default' and get whatever the user
> configured to be 'default' ?

yes, that works too. but most users (and your example) don't define "default".

> Very well, but the .asoundrc syntax seems to be in terms of
> duplex devices. How would you configure a plugin in 'default's
> capture stream only ?

the capture stream only exists when a process opens the device for
capture. it is not a separate property or entity. the properties of
the stream depend on the name of the device.

> Vor uns liegt ein weites Tal, die Sonne scheint - ein Glitzerstrahl.

so does this quote predate kraftwerk or are you finally embracing the
frozen four? :)


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