[mythtv] [mythtv-commits] Ticket #7517: Separate Volume control from Audio Output

[Ed W]

> The second feature is provided by the "software" volume control. Whilst it results in potentially lower quality audio, software volume control is generally favourably to no volume control at all and is therefore provided as a fallback.

Actually, I think you will find very few soundcards actually have a 
mixer which operates in the analogue domain?  In general when you adjust 
your alsa mixer levels the soundcard is doing a software volume control 
on the card...

However, there still can be differences in "software" volume control 
implentations, eg when reducing the levels a fair bit then you can get 
better quality operating on float or int32 samples than you can 
operating on 16bit int samples.  The quantisation gets reasonably 
significant fairly quickly on an int16 (you need to add dither at 
least).  Ideally you want to be operating on float/int32 samples if you 
are doing software volume (and never convert back down to int16).

(One of the nice things about the mythtv jack implementation at present 
is that it gets the samples converted to be floats quite early on and 
keeps them like that all the way through the audio chain right up to the 
soundcard.  Some soundcards unfortunately convert back to int16 at that 
point, but better quality soundcards will allow you to pass float right 
the way through.)


Just trying to clarify something that seems often misunderstood?

Cheers

Ed W