[asterisk-bugs] [Asterisk 0005186]: [patch] Zaptel idles channels with a value that isn't appropriate for alaw

[noreply at bugs.digium.com]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=5186 
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Reported By:                stevedavies
Assigned To:                markster
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Project:                    Asterisk
Issue ID:                   5186
Category:                   Core/General
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     closed
Asterisk Version:           I did not set the version :( 
SVN Branch (only for SVN checkouts, not tarball releases): N/A 
SVN Revision (number only!):  
Disclaimer on File?:        Yes 
Request Review:             Yes 
Resolution:                 fixed
Fixed in Version:           
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Date Submitted:             09-11-2005 05:17 CDT
Last Modified:              06-07-2008 11:04 CDT
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Summary:                    [patch] Zaptel idles channels with a value that
isn't appropriate for alaw
Description: 
Hi,

I've just been doing some experiments on my test box with looped E1 PRI 
spans - playing with app_test with a view to adding more tests.

In the process I "Monitor"ed to disk the audio heard on both ends of my
bridged call.

When I loaded the audio into Audacity to take a look, I was suprised to
see that a channel that isn't being transmitted on seems to be seen at the
receiving end as non-zero samples.  So every time the sending box starts
and stops sending audio then there is a jump of the "zero level" to true-0
and then back to the resting value.

The "resting value" is 832, which I note is AST_ALAW(255)

By contrast, AST_ULAW(255) is 0.

od -x </dev/zap/1 shows that channels not otherwise in use receive nonstop
0xff.  (IE - channels not otherwise written to are transmitted as 0xff).

So for channels that are being used for alaw, the "rest value" shouldn't
be 0xff but rather 0xd5, being AST_LIN2A(0).

I've attached what turned out to be rather a simple patch to fix this
issue.

Steve

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---------------------------------------------------------------------- 
 svnbot - 06-07-08 11:04  
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Repository: dahdi
Revision: 773

U   trunk/zaptel.c

------------------------------------------------------------------------
r773 | kpfleming | 2008-06-07 11:04:22 -0500 (Sat, 07 Jun 2008) | 2 lines

ensure that idle audio channels transmit silence (issue
http://bugs.digium.com/view.php?id=5186, slightly
different fix)

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http://svn.digium.com/view/dahdi?view=rev&revision=773 

Issue History 
Date Modified   Username       Field                    Change               
====================================================================== 
06-07-08 11:04  svnbot         Checkin                                      
06-07-08 11:04  svnbot         Note Added: 0088069                          
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