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Re: [Ant-phone-devel] Latency, fragments and their sizes.


From: Bruno Hertz
Subject: Re: [Ant-phone-devel] Latency, fragments and their sizes.
Date: 14 Feb 2004 18:59:22 +0100

Roland

thanks very much for your patience. Still, I didn't fully understand
one of your remarks:

> This is also a known problem. We will need a better dynamic speed drift
> compensation. The ISDN and dsp devices don't run in sync.

How exactly can they run out of sync? As I understand it we have
the following two basic input processing chains:

 voice -> mic -> soundcard -> dsp device -> ant -> idsn device
 idsn device -> ant -> dsp device -> soundcard -> line out

where ant in both cases does simple read and writes as much real
time as possible. I.e. in case there is no extensive buffering in
either the isdn or sound drivers (and ant, of course) my understanding
is there should be only millisecs delay from voice to isdn and from
isdn to line out, at least in an ideal world :) Or in other words,
the dsp is just a 'push through' device with drivers (hopefully)
optimized, besides other things, for minimum latency. This may be
a pretty basic question, but I really don't see the point to hook in
for a possible drift compensation.

One further question: could the call distance have an impact on
those delays? My yesterday call for example was Zürich-Flensburg,
and I have trouble to reproduce those extensive delays with local
calls. I.e. when I call myself, except a little latency everything
works just fine (which by the way suggests that application and driver
performance in general seem to be sufficient). So if you too did
observe varying behaviour depending on call distance, maybe you have
an idea what the reason might be?

And a last question: did you already test ant on a preemptible patched
kernel? If so, did it make any difference?

Btw in case you consider my questions too 'newbie' I'd appreciate
pointers to isdn/sound documentation which might help me improving
my understanding and level of discussion.

Thanks, Bruno.






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