[pulseaudio-discuss] [PATCH v2 5/5] alsa-mixer: Improve volume handling for Terratec Aureon Dual USB

[Alexander E. Patrakov]

18.04.2015 01:26, Tanu Kaskinen wrote:
> This card can be used in analog or digital mode, and in the digital
> mode there's no hardware volume or mute support. With the default
> configuration PulseAudio only sees a single "speaker" port, and
> assumes that controlling the Speaker element has some effect, which
> is not true in the digital mode. To work around this, let's add a
> special path configuration for this card to disable hardware volume.
>
> It would be better to disable hardware volume only in the digital
> mode, but I believe there's no way to automatically figure out which
> mode is in use, and requiring the user to tell which mode is in use
> at any given time would not be user-friendly.

I have one concern with this plan. You are going to always use software 
volume on a high-end card, and default to 30%, which is around -30 dB. 
So you have just robbed 5 bits out of the DAC resolution. Due to the 
fact that internal processing in PulseAudio is most likely based on 
16-bit samples in this use case, the DAC effectively becomes only 
11-bit, and without proper dithering. I am not sure whether owners of 
the said card will appreciate that.

So effectively, you are trading one bug for another. Sorry, I don't have 
any easy and constructive suggestions.

Does the card support 32-bit input samples? [that was the solution to 
the same kind of problem in the plug+softvol+dmix era that was 
implemented on my request in 2008]

-- 
Alexander E. Patrakov