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Broken/distorted inbound voice Yealink T46U

peter sutcliffe

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I have a PBX with a variety of Yealink handsets. 6x T42S, 2x T46S with expansion modules and 7x T46U with expansion modules.

PBX was working fine on the previous version 66 and was upgraded by the host to 68.0.2 and we start to get problems which normally sound like the adaptive jitter buffer type of Dalek sounds. The broken audio is only inbound to the handset and intermittant in nature.

I have set the jitter buffer to static and various attempts of 120, 180 and 240ms. all with the same complaint from the users. Echo cancellation is turned off as well.

These T46 handsets are all autoprovisioned so I have reprovisioned one from the most vocal user and await their feedback. I am hoping that something has changed with the templates and an autoprovision might fix the issue. It did change the ringtones which they also sooked about.

I dont think it is a bandwidth issue as it on a fiber NBN service here in Australia and while not high bandwidth, the downstream is greater than the upstream at the site.

Transport is UDP, and the preferred CODECS are PCMA and G.729.

I am fresh out of ideas and the host can find no issue in the PCAPs they are taking of the calls.

Anyone have any other ideas that may help?

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I would make a PCAP and try to play it back from there to see if the audio stream in theory sounds fine. That might help getting an idea what could be wrong. Sometimes the codecs for sending and receiving are different and this causes issues, though the Yealinks are generally quite well at dealing with this.

Generally, the Yealink templates work fine especially in the area of audio. I would be surprised if changing jitter buffer settings would improve anything. You could also try a newer Yealink firmware; there were some changes in the audio part, maybe they will make a difference. 

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