CUC 7x G729 Audio Quality Issues

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Jun 1st, 2009
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I am running CUC 7.x and am having some audio quality issues when using G729. The problem seems to be enhanced when a caller coming in on a G729 gateway to Unity records the message then it is played by a subscriber using G729 to talk to Unity. In this case, the distortion is effectively "doubled" and seems more noticeable. All QoS is in place and there are no issues with IP Phone voice quality on G729, only when having conversation with Unity. G711 conversation with Unity is fine. We are only using G711 and G729 in our environment. Any ideas? Thanks

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culittle Mon, 06/01/2009 - 06:18
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I would start by using the troubleshooting guide to see if you can gather additional information.

I would suspect that internal calls are working, and that only external calls coming in through the gateway are having issues. Defining the good path vs. the failing call path should be helpful.

j.burwell Mon, 06/01/2009 - 06:32
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Thanks, we have been going through this document and have not hit it yet. It does not seem to matter where the calls come from, if it is G729 to Unity it is garbled. For example, if a G729 user records their greeting, it is garbled as well.

Tommer Catlin Mon, 06/01/2009 - 06:30
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Is it through PSTN or IP phone or both? I have found on the CUCM 6.x and 7.x, the Wideband codec is enabled system wide for some reason. This causes some noticeable audio issues compared to g711. I would change the enterprise parameter to off and ensure g711 is being used on the IP phone and test again.

j.burwell Mon, 06/01/2009 - 06:34
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Thanks for the response. The problem is PSTN and IP phone, if they use G729. Everything is fine when PSTN and IP Phone use G711. We had already changed the Wideband parameter when we deployed this version of Callmanager.

Tommer Catlin Mon, 06/01/2009 - 06:36
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Id say since the codec is being changed at the CUCM, and other G729 calls are not affected, there seems to be something in the CUC. Is this a new problem?

j.burwell Mon, 06/01/2009 - 07:09
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This CUC deployment is about 9 months old but we only recently started deploying remote sites with G729 and that is when we started seeing the issues. Before that everything was G711 so we were fine.

whanson Mon, 06/01/2009 - 08:12
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Take a local phone and change the region to a remote region to use 729. This will eliminate all gateway and wan issues and put the problem squarely in Unity's lap. As Unity does the transcoding natively, did you see this problem after several conversions to 729 or right away no matter how many folks were using that codec?

whanson Mon, 06/01/2009 - 08:17
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Another suggestion, depending on how far you want to go with this, is to put the vm ports in a vm region and use only 711 to that region. usage on your wan would depend on how many concurrent vm you think you might have or are you saying you get garbled local phone to remote phone or remote pstn to local phone too?

j.burwell Mon, 06/01/2009 - 09:51
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I have adjusted so the phone is talking G729 directly to Unity and I still get the garbling. I will use your tip for the seperate Region workaround if I have to. Thanks for that tip.

I just changed the recording format on Unity from G729a to G711mu-law. Even though this is the recording format only and still G729 stream to Unity, it seems to be improving things. I just wonder what the storage impace will be if I leave it on G711mu-law. I also have a TAC case open and am awaiting feedback.

Thanks Jason

whanson Mon, 06/01/2009 - 10:29
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I would not store in 729 unless that is the majority of your users. Shouldn't have a major impact on storage.

lolu.oshunbiyi@... Tue, 06/02/2009 - 08:13
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I had a similar problem with CUCM 6.1 CUC 7.0(2) where where calls came in via an H323 trunk running G729. I had set the recording codec to G729a and the customer complained of poor audio quality with voicemail messages. It seems looking at a design guide for unity connections, the way things work is that every G729 call is transcoded to PCM linear then encoded to G729a:

g729->PCM->PCM (apply AGC)->g729a

Since all calls are converted to 16 bit PCM even if the recording and line codec are the same,and since g729 is a lossy codec, each transcode will decrease the quality. I assume this is having an adverse effect. I too have changed the recording format to G711 and have seen an improvement.




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