Re: [Alsa-user] "bit perfect" audio; was: what provides libasound_module_pcm_plughw.so

[Sergei S. <ste...@li...>]

On Wed, 15 Apr 2009 09:02:37 -0500
Matt Garman <mat...@gm...> wrote:

> On Tue, Apr 14, 2009 at 10:39:55AM +1200, Eliot Blennerhassett wrote:
> > without a default alsa.conf, plughw doesn't exist.
> > It is composed of the "plug" on top of "hw".
> > On my system it is defined in /usr/share/alsa/alsa.conf
> > 
> > you might try
> > 
> > pcm.!default {
> >         type plug
> >         slave.pcm {
> >                 type hw
> >                 card 0
> >                 device 0
> >                 subdevice 0
> >         }
> > }
> 
> I have a default alsa.conf in the same location as you.
> 
> But, your suggestion did work!  Thank you.
> 
> Now I have another question: my original goal in using just "hw" was
> to send "bit perfect" data to the DAC on my soundcard (i.e. no
> software-based alteration of the data/feed the soundcard exactly the
> raw audio).  The data is just CD digital audio, which I believe is
> signed 16 bit little endian/44100 Hz.  And then I found that my
> soundcard doesn't natively support that.
> 
> Now that I'm using plughw---which does any necessary format/rate
> conversions---am I really any better than using dmix?
> 
> In other words, is the only difference between dmix and plughw that
> dmix will mix multiple streams?  I don't mean to trivialize mixing
> multiple streams, but from my perspective, I'm looking for the best
> sound quality for only one audio stream.
> 
> So, an even more general question, are there any other sound
> "purists" out there, trying to directly use "hw" for bit-perfect
> audio?  What hardware do you have, what has been your experience,
> etc?
> 
> Thanks,
> Matt
> 
> 

If you do not change sample rate, but just increase number of bits,
e.g. 16 -> 24, you lose nothing.

Regards,
  Sergei.