[hylafax-users] [asterisk-users] asterisk, iaxmodem, hylafax quality problem

Artifex Maximus artifexor at gmail.com
Fri Sep 22 06:55:50 MST 2006


On 9/21/06, Lee Howard <faxguy at howardsilvan.com> wrote:
> Artifex Maximus wrote:
> > Everything is fine when caller use ECM but when ECM isn't in use I
> > often got unusable incoming faxes (much often that it should be). But
> > when I switch back to fax machine that receive faxes perfectly (at
> > least no visible error).
> The fax machine itself uses ECM, undoubtedly.
That's unfortunately not the case. The remote doesn't asks for ECM so
that's disabled or missing on that machine. In this situation fax
machine is produce better output and I don't know why. Might a better
DSP algo?

> If callers that have
> quality problems with IAXmodem+HylaFAX don't have problems with the fax
> machine, then that strongly indicates that something is wrong with your
> Asterisk setup... corrupting the audio.  Usually this is due to resource
> constriction of the Zap device, zttest scores less than 99.98% is
> indicative of that situation.
I don't find any info that zttest is destructive or not on an active
system. I mean that currently active calls are disturbed or not while
zttest running. I can't stop system now. I look into zttest source and
find that zttest is using /dev/zap/pseudo but I don't know this
'pseudo' channel is related to any 'real' channel or not.

> > Where should be the problem? Is there any solution for improving
> > quality? Any tuning in Asterisk or Hylafax? As I see some people use
> > slinear for iaxmodem and some user use alaw. Which is better?
> There is no functional difference between using uLaw, alaw, or
> slinear... except that using slinear reduces the need for conversion...
> and thus possibly lessens CPU usage very slightly.
I see. I leave it on slinear.


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