[linux-audio-dev] Merging digital sampling sessions

[David Kastrup]

Lee Revell <rlrevell at joe-job.com> writes:

> On Sat, 2005-12-10 at 22:52 +0100, David Kastrup wrote:
>> I have a minidisc player with S/PDIF output and an ALSA supported
>> soundcard (details if the card are not really important for the
>> problem at hand).
>> 
>> I sample recordings via
>> 
>> arecord -D spdif -f cd
>> 
>> Ok, and here is the rub: playback is not perfect, and neither seems to
>> be the sampling.  Probably at times error interpolation sets in,
>> probably at times samples get lost or replicated.  Not much, perhaps
>> once per minute or so.  This leads to audible clicks, of course. 
>
> Well, it would be better to figure out why arecord doesn't work than try
> to work around it.
>
> Use "arecord -v -D spdif -f cd" and see if a rate conversion plugin is
> used.  The ALSA SRC is not great so if that is the case then you'll get
> better results sampling at 48KHz (-f dat) then downsampling to 44.1
> afterward.

Does not appear to be the case, and anyway, there would not be a
reason that rate conversion leads to glitches.  Here you are:

Recording WAVE 'stdout' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo
Hardware PCM card 0 'C-Media PCI CMI8738-MC6' device 2 subdevice 0

Its setup is:
stream       : CAPTURE
access       : RW_INTERLEAVED
format       : S16_LE
subformat    : STD
channels     : 2
rate         : 44100
exact rate   : 44100 (44100/1)
msbits       : 16
buffer_size  : 16384
period_size  : 4096
period_time  : 92879
tick_time    : 1000
tstamp_mode  : NONE
period_step  : 1
sleep_min    : 0
avail_min    : 4096
xfer_align   : 4096
start_threshold  : 1
stop_threshold   : 16384
silence_threshold: 0
silence_size : 0
boundary     : 1073741824
Aborted by signal Interrupt...

On another note: it would seem like a simple enough task to let the
recording start with the first non-zero sample.  I have been
completely unable to make head or tails of the manual page
descriptions of the arecord options presumably intended for that and
have found absolutely no setting that would not either drop quite more
than just the initial zeros, or not drop anything at all.

I'd also like to prune trailing zeros at some point of time.  arecord
does not seem to have options for doing that, I guess.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum