[pulseaudio-discuss] Routing of audio to loudspeakers or headphones

Mark Brown broonie at sirena.org.uk
Tue Aug 31 06:31:42 PDT 2010

On Fri, Aug 27, 2010 at 08:49:16AM +0000, Kim Therkelsen wrote:

[Please fix your MUA to word wrap within paragraphs, it makes your
messages vastly more legible.]

> > No, DSP in kernel will never be accepted upstream. ALSA supports doing
> > DSP at the application layer, though PulseAudio bypasses all the setup
> > for that by default.

> I do not really understand what you mean by "No, DSP in kernel will
> never be accepted upstream". 

Code which does signal processing on the CPU in kernel space will never
be accepted by the ALSA developers.

> What I want is to make is a DSP module that improves the sound quality
> of the sound coming from the laptop builtin speakers by applying DSP

Sure, this was clear.

> What I really want to know is:

> Where can I place this module: 

> As a plugin to PulseAudio? 

Pulse should be able to do this.

> Some other type of plugin? 

You could do an ALSA plugin, though Pulse would require some persuasion
to run with it.

> As a kernel module? 

This will not be accepted.

> In the audio driver?

The audio drivers are mostly in kernel.

> My requirements:

> 1) Must be able to detect if headphones are connected

Note that it's not just a case of checking if they're plugged in - you
also need to check that the signal you're interested in is going via

> 2) Must be able to process stereo and multichannel (5.1/7.1) formats. I need the multichannel formats to perform my binaural downmixing to stereo.

You want to be somewhere in application layer for all of this.

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