[alsa-devel] SALSA and aplay

[Takashi Iwai]

At Thu, 19 Jul 2007 15:24:40 +0100,
John Rigg wrote:
> 
> On Thu, Jul 19, 2007 at 11:33:32AM +0200, Takashi Iwai wrote:
> > At Wed, 18 Jul 2007 17:20:29 +0100,
> > Alan Horstmann wrote:
> > > 
> > > On Wednesday 18 July 2007 16:01, Alan Horstmann wrote:
> > > > Yes and yes.  Using "hw" gives the same wrong speed with -lasound, and
> > > > standard command-line aplay does also.  Evidently I understand even less
> > > > than I thought.  I had expected that with the card hardware set to 44100Hz
> > > > and locked, that playing a 44100Hz file would be straightforward.  Maybe
> > > > the file is not right.  I may have to pause testing for a few days now.
> > > 
> > > Actually, I think I have an idea what is happening, but not why.
> > > 
> > > aplay -v TMP/try3.wav
> > > 
> > > Playing WAVE 'TMP/try3.wav' : Signed 32 bit Little Endian, Rate 44100 Hz, 
> > > Channels 10
> > > Plug PCM: Rate conversion PCM (48000, sformat=S32_LE)
> > > Its setup is:
> > >   stream       : PLAYBACK
> > >   access       : RW_INTERLEAVED
> > >   format       : S32_LE
> > >   subformat    : STD
> > >   channels     : 10
> > >   rate         : 44100
> > >   exact rate   : 44100 (44100/1)
> > >   msbits       : 32
> > >   buffer_size  : 5644
> > >   period_size  : 940
> > >   period_time  : 21333
> > >   tick_time    : 0
> > >   tstamp_mode  : NONE
> > >   period_step  : 1
> > >   sleep_min    : 0
> > >   avail_min    : 940
> > >   xfer_align   : 940
> > >   start_threshold  : 5640
> > >   stop_threshold   : 5644
> > >   silence_threshold: 0
> > >   silence_size : 0
> > >   boundary     : 1479540736
> > > Slave: Direct Stream Mixing PCM
> > > Its setup is:
> > >   stream       : PLAYBACK
> > >   access       : MMAP_INTERLEAVED
> > >   format       : S32_LE
> > >   subformat    : STD
> > >   channels     : 10
> > >   rate         : 48000
> > >   exact rate   : 48000 (48000/1)
> > >   msbits       : 24
> > >   buffer_size  : 6144
> > >   period_size  : 1024
> > >   period_time  : 21333
> > >   tick_time    : 0
> > >   tstamp_mode  : NONE
> > >   period_step  : 1
> > >   sleep_min    : 0
> > >   avail_min    : 1024
> > >   xfer_align   : 1024
> > >   start_threshold  : 6144
> > >   stop_threshold   : 6144
> > >   silence_threshold: 0
> > >   silence_size : 0
> > >   boundary     : 1610612736
> > > Hardware PCM card 0 'TerraTec DMX6Fire' device 0 subdevice 0
> > > Its setup is:
> > >   stream       : PLAYBACK
> > >   access       : MMAP_INTERLEAVED
> > >   format       : S32_LE
> > >   subformat    : STD
> > >   channels     : 10
> > >   rate         : 48000
> > >   exact rate   : 48000 (48000/1)
> > >   msbits       : 24
> > >   buffer_size  : 6553
> > >   period_size  : 1024
> > >   period_time  : 21333
> > >   tick_time    : 1000
> > >   tstamp_mode  : NONE
> > >   period_step  : 1
> > >   sleep_min    : 0
> > >   avail_min    : 1024
> > >   xfer_align   : 1024
> > >   start_threshold  : 1
> > >   stop_threshold   : 1717829632
> > >   silence_threshold: 0
> > >   silence_size : 1717829632
> > >   boundary     : 1717829632
> > > 
> > > It attempts to set the card to 48000, which fails since I have it locked!  
> > > When I recorded the file the same was true, so from "default" the file plays 
> > > back correct although it is in fact wrong, and plays wrong when imported into 
> > > Audacity.  The set-up listed above suggests to me that Alsa is rate 
> > > converting to 48000 and Mmap'ing to the card.  If correct, is that really 
> > > necessary?  I dislike any rate conversions on a serious recording system, and 
> > > especially hidden ones.  Is this a configuration issue that might have 
> > > changed since, say, 1.0.10 or 1.0.12?
> > 
> > The 48k-fixed rate is due to dmix plugin.  It requires a fixed sample
> > rate for all apps.  In theory, it may accept multiple rates, but the
> > feature is not implemented yet.
> > 
> > You can change the default rate by overriding defaults.pcm.dmix.rate
> > config item, e.g. define the below in ~/.asoundrc:
> > 
> > 	defaults.pcm.dmix.rate 44100
> 
> Wouldn't it be better to specify hw:0 (or whatever card you are using)
> in this case? With this type of hardware I'd rather make sure that dmix
> isn't used at all (I assume that dmix is now the default instead of
> hw:0).

Well, you can claim that because you don't get bug reports or rants ;)

The only reason that plug+dmix is used is that it can handle most
cases without hitches.  It works as it is.  That's all above other
reasons.


Takashi