Voicemail message quality on SIP trunks only

[ipoJT]

Having an issue with poor quality voicemail messages received on Gamma SIP trunks. General realtime call quality is good, with no cause for concern.
Messages left internally are perfectly fine, when retrieved at handsets (IP1608 and POTs) and by email with .wav attachment.

Actions so far:
Tested on both Embedded and VMPro platforms.
Amended Codec to Gamma SIP trunk, IPO SIP config and IP1608s to G729.
Swapped ports on LAN switch.
Swapped out 500v2 CCU

Despite the above, this has not resolved and I'm running out of ideas. Have seen this old post, but was wondering if anyone else had any advice on this..?

http://www.tek-tips.com/viewthread.cfm?qid=1690534

Many Thanks

 

[IPGuru]

G729 is a compressed codec, for best speech quality you should probably try G711


Do things on the cheap & it will cost you dear

 

[ipoJT]

Thanks IPGuru, previously we were all setup for G711, but the issue was still apparent. Bizarrely it only affects voicemail, received messages and when attempting to re-record VM greetings remotely, over SIP trunk. Never had a complaint about speech quality and I have made plenty of calls to the customer. Internally messages are crystal clear. Have requested Gamma move trunk to another SBC, but they claim it won't fix it.

For further testing purposes, SIP trunk configured to LAN2 with no NAT configuration, but same issue persists.