VoIP MOS Score: What It Means and How to Fix Bad Call Quality

Last updated: March 2026 | Reading time: ~20 minutes You're getting complaints. Agents say calls sound "robotic." Leads say they can't understand the agent. Your QA team flags recordings where half the words are garbled. Someone says "we need to check the MOS score" and nobody in the room knows what that means. MOS — Mean Opinion Score — is the standard metric for voice call quality. It runs from 1.0 (completely unintelligible) to 5.0 (perfect, indistinguishable from an in-person conversation). It was originally measured by having actual humans listen to calls and rate them. Now it's calculated algorithmically from network statistics. In a call center running VICIdial, your MOS score directly affects conversion rates. An agent talking to a lead through a choppy, laggy connection loses trust in the first 10 seconds. The lead assumes you're a scammer calling from a boiler room overseas and hangs up. Here's everything you need to know about MOS scores, how to measure them, and how to fix