[asterisk-bugs] [Asterisk 0016017]: v23 caller id detection (UK) less than 100%

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=16017 
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Reported By:                troublebot
Assigned To:                
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Project:                    Asterisk
Issue ID:                   16017
Category:                   Channels/chan_dahdi
Reproducibility:            sometimes
Severity:                   minor
Priority:                   normal
Status:                     acknowledged
Asterisk Version:           1.4.26.2 
JIRA:                        
Regression:                 No 
Reviewboard Link:            
SVN Branch (only for SVN checkouts, not tarball releases): N/A 
SVN Revision (number only!):  
Request Review:              
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Date Submitted:             2009-10-05 06:48 CDT
Last Modified:              2009-10-08 17:50 CDT
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Summary:                    v23 caller id detection (UK) less than 100%
Description: 
Around 1 in 100 will fail with callerid.c: No start bit found in fsk data

After implementation of polarity detection in wcfxo.c I initially believed
there was an issue with my implementation or the hardware (X100P SE). I
setup enhanced logging and data capture and discovered that this was not
the case. There is a certain amount of noise present most of which could be
removed with a band pass filter, which I believe should help detection
rates. I do not believe the noise is inherent in the line, most of the
noise can be characterised as low frequency noise (mentioned in si3034 spec
as dc offset) and 4khz squeal. I have the raw data captured directly from
wcfxo if there is any interest in improving this. 
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 (0112090) davidw (reporter) - 2009-10-08 17:50
 https://issues.asterisk.org/view.php?id=16017#c112090 
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This is too far from my company's area of interest for me to spend much
time on, but if someone wants to experiment, the two possible strategies I
would investigate, for the V.23 tones, are:


Use length 7 FIR filters, with complex coefficients
(a+b*z+c*z**2....+g*z**6).  I suspect the best values are exp(2*pi*f*t*i),
for t from -3/8000 s to +3/8000 s.  I have a suspicion that there is no
need to apply a windowing function here.  You may need to apply a frequency
dependent overall correction. (z**n means the input delayed by n samples).

Take the modulus of each result, and take the difference of these.  When
it crosses a certain positive threshold in the positive direction, toggle
the output one way, and do the opposite on crossing the corresponding
negative threshold.

As a rather different method, threshold the time between successive zero
crossings against 1/3600th of a second. 

Issue History 
Date Modified    Username       Field                    Change               
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2009-10-08 17:50 davidw         Note Added: 0112090                          
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