[LAD] ALSA audio

Will Godfrey willgodfrey at musically.me.uk
Sat Mar 7 19:01:16 UTC 2015

On Sat, 7 Mar 2015 17:46:12 +0000
Fons Adriaensen <fons at linuxaudio.org> wrote:

> On Sat, Mar 07, 2015 at 05:18:41PM +0000, Will Godfrey wrote:
> > I've just been reading the ALSA Programming HOWTO by Matthias Nagorni and one
> > detail caught my attention immediately. This is the idea of using plughw instead
> > of directly addressing your soundcard.
> > 
> > On the face of it this seems *much* easier, but there surely must be a catch.
> > Can anyone explain what the downside of doing this might be?
> That HOWTO must be at least ten years old now. 
> It is not 'much easier', the API is the still the same.
> The difference is that the plug layer will try to hide
> the real configuration space of your HW, allowing you
> to use almost any combination of sample rate, sample format,
> period size, etc. The downside is that you have no control
> over what is really happening. It also seems to interfere
> with the strict timing that low-latency period-synchronous
> systems such as Jack more or less require. 
> In theory it should be possible to stack or combine the
> various ALSA 'plugins' in arbitrary ways. In practice most
> combinations do not work very well or at all. IMHO this
> part of ALSA is a failure.
> If the ALSA API seems too much too handle, use a library
> such as zita-alsa-pcmi to take care of the complexity, and
> use it with a hw: device, not a plughw: one. All my apps 
> that provide access to ALSA directly (rather than via Jack)
> use it - it replaces around a thousand lines of code in each
> of them and provides a very easy to use interface. 
> Ciao,

That was fast :)

Thanks for the info. Just tried the examples. They certainly seem to be

... they also proved that I was 'doing it wrong' and a KA6 USB card is

Will J Godfrey
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.

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