QOS Parameter questions

[cjk03b]

We have been looking at the Zoom Phone system QOS to determine why some clients are reporting poor sound quality occurring 1-2 times per week. To be more specific, callers are reporting that our user sounded distorted or echo-ey while we heard clearly from them. We ran a certification on the wired network ports, patch cables, and phone cables. We were able to look at specific events, and the QOS showed that they were 4.1-4.5 good quality calls. The only commonality I could see between them was that they all showed a 12kbps sending bitrate when known good calls showed a 50-75kbps sending bitrate.

Zooms website says that bandwidth needs are 60-100kbps for calls.

Could this actually be the cause of the poor sound quality? If the recommended bandwidth is 60-100 kbps, why is it rating a 12kbps call is good quality?