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

[Artifex Maximus]

Hello,

My setup is PRI card, Asterisk, iaxmodem, hylafax or PRI card,
Asterisk, channel bank, fax machine. I'm using Fedora Core 4, iaxmodem
0.1.14, hylafax 4.3.0, asterisk 1.2.10.

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).

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?

What config should I post if that needed for ideas?

bye,
Zsolt