Re: PCM hw mixing with volume

[James Courtier-Dutton <James@superbug.demon.co.uk>]

Ove Kaaven wrote:
> 
> 
> Well, the requirements that raised this thread should be fairly clear.
> For example,
> 
> ALTERNATIVE 1
> 
> snd_pcm_set_volume(snd_pcm_t* pcm, int volume)
> 
> and
> 
> snd_pcm_set_pan(snd_pcm_t* pcm, int pan)
> 
> using whatever value range makes the most sense, and perhaps some query
> on whether these controls are available from the pcm info. It's
> acceptable to have to explicitly ask for these controls using hw_params.
> The plug plugin could insert the route/volume plugin if these controls
> are asked for.
> 
> ALTERNATIVE 2
> 
> snd_pcm_set_volume(snd_pcm_t* pcm, int vol_left, int vol_right)
> 
> but I don't expect this to be useful, since there are probably some
> oddball devices out there that aren't able to control left and right
> volume independently like this.
> 
> ALTERNATIVE 3
> 
> Let each PCM channel have its own mixer control, like the EMU10K1
> currently do. That is, use snd_pcm_info_get_subdevice() to get the
> index, then look up a volume control with a well-known name and the
> given index using the snd_ctl API to control the volume of that PCM
> stream. The name and semantics of that mixer control would have to be
> standardized and be the same on all devices that are capable of this
> feature.
> 

What about 7.1 surround sound channels. All your suggestions only assume 
2 PCM channels.

Although it might seem nice to add this to alsa, it is not exactly a 
difficult task for the application to do itself.

I suggested exactly what you suggested some time ago (see alsa-devel 
archives), but recently I have realised that there is little or no point.
The application will contain a user interface control for the volume, so 
one might as well adjust the volume in software as well. It is not even 
very CPU intensive.

Cheers
James


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