[Asterisk-Users] spandsp + HFC poor fax quality?

[Tomasz Chmielewski]

I've been trying to set up incoming faxes using spandsp with a HFC card.

Unfortunately, incoming faxes are of very poor quality, the pages are 
not transferred wholly (sometimes only a bit of a page is transferred etc.).

 From what I've read, I may have troubles with correct "timing" (and 
need to set up ztdummy etc.).

On the other hand, it is impossible to set ztdummy if one uses zaphfc 
module (HFC card) - because with HFC cards, ztdummy/timing is not needed.

I tried different libtiff versions with spandsp (ending with 3.7.2 which 
seems to be the latest), but I always get this issue (especially, when 
the fax contains images etc. more complicated stuff).

A typical fax session looks like that:

DCS with final frame tag
In state 9
Coarse carrier frequency 1699.82 (66)
Training error 0.406683
Training succeeded (constellation mismatch 0.417317)
Start rx document
Start rx page - compression 2
Coarse carrier frequency 1738.28 (6)
Training error 692.017653
Training failed (convergence failed)
Coarse carrier frequency 1699.86 (66)
Training error 0.394675
Training succeeded (constellation mismatch 0.417396)
DCS with final frame tag
In state 5
Coarse carrier frequency 1699.93 (66)
Training error 0.489383
Training succeeded (constellation mismatch 0.576316)
Start rx page - compression 2
Coarse carrier frequency 1699.84 (66)
Training error 0.339757
Training succeeded (constellation mismatch 0.509557)
EOP with final frame tag
In state 5
DCN with final frame tag
In state 8


Sometimes it ends with ghostscript errors:

     -- Executing System("Zap/1-1", "tiff2ps -2eaz -w 8.5 -h 11 
/var/spool/asterisk/fax/asterisk-3834-1116329874.0.tif | ps2pdf - 
/var/spool/asterisk/fax/asterisk-3834-1116329874.0.tif.pdf") in new stack
Error: /limitcheck in --setpagedevice--
Operand stack:
    --dict:1/1(L)--
Execution stack:
    %interp_exit   .runexec2   --nostringval--   --nostringval-- 
--nostringval--   2   %stopped_push   --nostringval--   --nostringval-- 
   --nostringval--   false   1   %stopped_push   1   3   %oparray_pop 
1   3   %oparray_pop   .runexec2   --nostringval--   --nostringval-- 
--nostringval--   2   %stopped_push   --nostringval--   1   3 
%oparray_pop   --nostringval--   --nostringval--   --nostringval--
Dictionary stack:
    --dict:1052/1123(ro)(G)--   --dict:0/20(G)--   --dict:88/200(L)--
Current allocation mode is local
Last OS error: 22
GNU Ghostscript 7.05: Unrecoverable error, exit code 1


I tried sending faxes from different fax devices, always the same issue.

So the last thing that comes to my mind is that my timing is still *not* 
fixed.
Anyone has an idea how to fix timing issues with a HFC card?

-- 
Tomek

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