[alsa-devel] SALSA and aplay

[Alan Horstmann]

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?

Can I prevent the rate conversion eg in conf file and still have control of 
format and channel numbers that "hw" prevents?  Or is this all down to the 
way aplay does things?

Alan