Bad quality on IVR/Custom prompts, but not when manually transferred


I got a very strange issue here… If we have a inbound route set to automatically put incoming calls into a IVR, Dial By Name, or anything with a recorded prompt, the outbound audio the caller hears is terribly distorted to the point of not being able to understand it. It sounds like a extremely over-compressed mp3. This applies to both the included voice prompts or custom recorded ones. Additionally, if they use the dial by name to get into someone’s voicemail, the voicemail prompts will also be extremely distorted.

However, if we manually transfer calls into the IVR, Dial By Name, Voicemail, etc… the audio quality is perfectly fine! It only happens if the transfer is made by the UCM automatically!

Setup is as follows:
UCM6204… GXP2170s phones. Voice service is SIP trunk delivered on a dedicated private Ethernet connection directly from our local fiber ISP’s fiber ONT. Phones are on their own dedicated switch and network wiring physically separate from the rest of the network. We never have any sort of call quality problems at all in day to day use on external or internal calls, no echo, bad quality, etc…

Anyone have any ideas?


Replying to my own post! After much ripping my hair out… I figured it out! Our SIP trunk provider only supports PCMU. However I had PCMU and a few other codecs in the Available box on the trunk settings. Removing all but PCMU solved the problem!

I am guessing it was trying to use a codec our trunk provider didn’t support when it auto-transferred.