[asterisk-bugs] [JIRA] (ASTERISK-23262) Audio degredation with codec_dahdi and ChanSpy'ing

[Shaun Ruffell (JIRA)]

    [ https://issues.asterisk.org/jira/browse/ASTERISK-23262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=214972#comment-214972 ] 

Shaun Ruffell commented on ASTERISK-23262:
------------------------------------------

Just putting my own comment on this issue from the discussions:  The current hypothesis (thanks jcolp) is that when the VOLUME(RX) call is on the channel there are potentially 3 calls to translate the audio in the path. The need to block on the hardware is accumulating which is not playing well with the jitter buffers on the end of the audio paths in Asterisk.

I wanted to look over the path to see if there is any way to eliminate blocking so much on the hardware in this case.
                
> Audio degredation with codec_dahdi and ChanSpy'ing
> --------------------------------------------------
>
>                 Key: ASTERISK-23262
>                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-23262
>             Project: Asterisk
>          Issue Type: Bug
>      Security Level: None
>          Components: Codecs/codec_dahdi
>    Affects Versions: SVN
>         Environment: Linux pbx-host 3.5.0-45-generic #68~precise1-Ubuntu SMP Wed Dec 4 16:18:46 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
> Dell PowerEdge R620
>            Reporter: Sean Bright
>            Assignee: Shaun Ruffell
>         Attachments: irc.txt
>
>
> The server has 2 TCE400P cards and I'm using the latest wctc4xxp driver from the DAHDI-Linux git repository (master branch).
> There are 3 channels involved in this scenario:
> * {{SIP/from-internal-user/1}}
> * {{SIP/from-external-user/1}}
> * {{SIP/from-spying-user/1}}
> The native format for all 3 of these channels is G729.
> {{SIP/from-internal-user/1}} enters dialplan and goes immediately into {{MusicOnHold}}.  The {{MusicOnHold}} class consists of only .g729 files, so no encoders/decoders are used at this point.
> {{SIP/from-external-user/1}} enters dialplan, and hit these three apps/functions in this order:
> * {{MixMonitor(<somefile>.sln,...)}}
> * {{VOLUME(RX)=2}}
> * {{Bridge(SIP/from-internal-user/1,...)}}
> Now, the third channel channel, {{SIP/from-spying-user/1}}, enters dialplan and goes into {{ChanSpy}}:
> * {{ChanSpy(SIP/from-internal-user/1,...)}}
> At this point, both {{SIP/from-internal-user/1}} and {{SIP/from-external-user/1}} begin to hear distortion/delay and are unable to understand each other.  There is also distortion/delay observed by {{SIP/from-spying-user/1}}.
> Spying on {{SIP/from-external-user/1}} does not cause the audio degredation.  Also, based on a suggestion by Josh Colp, removing the call to {{VOLUME(RX)=2}} appears to resolve the problem as well.

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