[ecasound] full-duplex sync

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Subject: [ecasound] full-duplex sync
From: John S. Denker (jsd_AT_research.att.com)
Date: Thu Oct 11 2001 - 22:18:59 EEST

Hi --

We need to do full-duplex. Simultaneous play + record.
It is absolutely essential to get the timing right.
We have hardware that is documented to support this; see
  http://www.midiman.net/support/manuals/pdf/DELTA1010.PDF
(Look in the middle of page 24.)

The alsa driver is supposed to support this, too; see e.g.
  http://www.alsa-project.org/alsa-doc/alsa-lib/group_pcm.html#a46

HOWEVER.... When I try to do this with ecasound, I find that there is
considerable run-to-run variability in the timing relationship between
the played and recorded signals.

I read the documentation and even grepped for terms like "sync" and
"full duplex" without success.

I looked through the ecasound code and grepped for likely terms
without success.

I searched the mailing-list archives. I found a lot of discussion
of MIDI-synch (which is !not! what I'm interested in) but not much
about full-duplex analog sync.

A secondary goal is to have minimal delay between play & record.
The primary goal is that whatever delay there is should be
absolutely stable and reproducible.

So....
-- Does ecasound have this capability?
-- If so, how do we invoke it?
-- If not, does anybody have any suggestions for what we should do???
   (There are several crude workarounds, but doing it right ought
   to be easier than kludging it.)

Thanks --- jsd 

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