Re: [ecasound] Help understanding -B -b and -z options

On Tue, 15 Feb 2005, Cassettes2CDs wrote:

> I do bunches and bunches of stereo 32-bit recording
> with ecasound and my M-Audio Delta 1010LT's. I
> currently do up to 8 stereo pairs at once, but don't
> need them to be -sychronized- with each other at all.

So are you using ALSA/asounrc and the multi-plugin, or the 4Front OSS
drivers, to provide the stereo pairs...?

> The recording process is very fragile, though, and if
> the computer does anything disk-y, I drop frames.

Hmm, have you compared recording invidual stereo pairs vs recording all
channels with single ecasound instance? The latter one should not
be fragile even on a not-so-well-tuned system.

> ecasound -z:db -r -b 8192 -f 32,2,44100,i -i /dev/dsp5
> -el valve,0.015,0.015 -f 32,2,44100,i -o filename.raw
[...]
> So my -z is "db," my -b is "8192," and I don't even
> use -B.

Basicly -B option selects the profile (i.e. which set of default
parameters to use for all buffering related options). The other options
(-z:db, -b, etc) then tune individual parameters.

A good intro to this topic can be found at:
http://eca.cx/ecasound-list/2001/10/0020.html

A link to above message is mentioned on the tutorials page at:
http://eca.cx/ecasound/Documentation/tutorials.html

Now as for reliability, -z:db protects against disk i/o scheduling
problems, while -b and -z:intbuf/-z:nointbuf help against kernel
process scheduling and interrupt latency related problems. For very
reliable recording, the following set of option should provide good
results in most cases:

ecasound -z:db,500000 -r -b:1024 -z:intbuf -f:32,2,44100,i -i /dev/dsp5 -o foo.raw

With -z:intbuf, the value of -b:xxx doesn't have a big impact anymore, as
then ecasound will in any case try to utilize maximum amount of sound
device buffering. With -z:intbuf, -b:xxx then just controls how often
interrupts are raised (1024-4096 are reasonable values, many soundcards do
not support higher values). I've also increased the disk i/o buffer to
50000 frames (default 100000). With 44100 srate, that's about +5secs of
buffering for "foo.raw" and other disk objects in the setup, which is
quite a lot.

But I also want to emphasize that normally you shouldn't need to specify
any of these options. Ecasound should be able to guess the right options
to use for most chainsetups.

-- 
  http://www.eca.cx
  Audio software for Linux!
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