Measuring VoIP Call Quality with Mean Opinion Score

As telecom infrastructure leaders move toward cloud platforms and SIP trunking, voice quality expectations remain high. Users still demand clear, uninterrupted conversations. If a call sounds muffled, delayed, or cuts out entirely, they notice. And if it happens more than once, trust in the service declines.

One of the most reliable ways to track and improve call clarity is through the Mean Opinion Score (MOS). For a deeper dive into end-to-end monitoring of SIP and VoIP failures, read our guide on VoIP monitoring and call failure.

In today's VoIP-driven communication environments, understanding how MOS is calculated, what affects it, and how to act on it can make or break your customer satisfaction strategy.

This blog explains what the mean opinion score (MOS) VoIP metric is, how it's calculated in modern networks, how to interpret the MOS 5 point scale, and how Klearcom enables proactive audio quality monitoring to ensure excellent user experience across global phone calls.

What is Mean Opinion Score (MOS)?

The mean opinion score (MOS) is a standardized measurement that rates the perceived quality of audio on a five-point scale. Originally designed as a subjective test by the ITU, human listeners would rate call clarity from 1 (Bad) to 5 (Excellent). The average of these ratings became the MOS.

Today, with billions of calls happening over VoIP networks, this subjective process has evolved. Most platforms now use algorithms that estimate the MOS score voice quality in real time. These models simulate how a person might experience and rate the call, factoring in network issues like jitter, delay, and packet loss, as well as the effects of compression from the audio codec in use.

Understanding the MOS 5 point scale is essential for interpreting results. A score between 4.0 and 5.0 indicates high-quality audio, often referred to as “toll-quality.” Scores between 3.6 and 3.9 are generally acceptable for most business needs but may include minor artifacts. Scores in the range of 3.1 to 3.5 suggest noticeable degradation that could affect customer interactions. Anything below 3.0 typically reflects severely compromised quality.

A high MOS score signals a clear, stable connection that meets user expectations. Scores below 3.5, on the other hand, suggest there is a significant issue impacting the call.

How is MOS Calculated in VoIP?

In modern networks, MOS is calculated either through intrusive or non-intrusive methods. Both approaches offer value, but each has specific use cases and limitations.

Intrusive methods rely on sending known audio samples through a call path. These samples are then compared to the received audio using algorithms such as PESQ or POLQA. While this method is precise, it is best suited for lab tests or scheduled environments. It does not scale well for continuous live call monitoring.

Non-intrusive methods do not require reference audio. Models like the E-model and ITU’s P.563 assess live audio or network metrics to estimate MOS. The E-model, for example, calculates MOS based on latency, jitter, codec type, and packet loss. P.563 evaluates the call audio itself, without comparing it to a reference.

Because non-intrusive models operate during live calls, they are ideal for VoIP monitoring platforms looking to maintain excellent quality of service (QoS) and ensure consistent user experience.

What Impacts MOS in VoIP Networks?

Voice quality in VoIP is influenced by several technical and environmental factors. While some are within your control, others may lie with external providers or carriers.

Latency is a major contributor. When one-way delay exceeds 150 milliseconds, conversations feel unnatural. Participants often interrupt or talk over each other. This disrupts communication flow and reduces overall user experience.

Jitter introduces inconsistency in packet arrival times. Even when jitter buffers are in place, high variation can result in uneven or choppy audio.

Packet loss is particularly damaging to audio quality. Missing even a small percentage of packets during a voice call can create gaps, clipped words, or robotic-sounding speech. This kind of degradation significantly reduces the perceived quality of service.

The choice of audio codec also plays a critical role. Codecs like G.711, which are uncompressed, provide high MOS score voice quality but require more bandwidth. Compressed codecs such as G.729 reduce bandwidth usage but limit maximum achievable MOS. Wideband codecs like Opus and G.722 offer enhanced clarity but must be supported across all segments of the call path.

Lastly, endpoint devices and environments can affect MOS. Low-quality headsets, microphone echo, or background noise can lower the MOS, even if the underlying network is performing well. This is especially relevant in remote work settings, where audio environments are inconsistent.

Why Traditional MOS Testing Falls Short

Legacy tools like PESQ and POLQA work well in lab conditions. However, they do not capture the full spectrum of real-world challenges. These tools require reference audio and are typically limited to predefined intervals or static testing environments.

They are not designed to detect issues like transient network congestion, region-specific carrier problems, or endpoint device malfunctions. As a result, they often miss the actual problems your users experience during live calls.

Measuring MOS in production, across real call paths, is the only way to truly understand and respond to quality issues as they occur.

Why MOS Monitoring Matters for Customer Experience

The quality of voice interactions directly impacts how customers perceive your brand. In contact centers, even a slight drop in audio quality can frustrate callers. Repeating information, dealing with dropped words, or struggling to understand an agent creates a negative experience.

Customers rarely report these issues. Instead, they quietly take their business elsewhere. That makes it critical for telecom and IT teams to detect voice degradation before it becomes visible in satisfaction scores or churn metrics.

Improving call quality starts with treating MOS as a business-critical performance indicator. This means continuously monitoring voice performance, setting clear alert thresholds, and trending metrics over time. By observing how MOS varies by region, carrier, or device type, teams can isolate root causes and take focused corrective action.

Introducing Klearcom’s Neural Voice Quality Algorithm (NVQA)

To enable real-time visibility across global call paths, Klearcom developed the Neural Voice Quality Algorithm (NVQA). Unlike traditional approaches, NVQA uses a neural model to analyze live audio and provide MOS estimates without reference audio.

This allows it to detect subtle and complex patterns affecting audio quality, including latency fluctuations, intermittent jitter, background noise, echo, and signal clipping. Because it operates in real time across mobile, VoIP, fixed-line, and toll-free networks, NVQA delivers continuous insight into what customers actually experience.

By implementing NVQA, telecom teams gain the ability to monitor MOS globally, receive immediate alerts on quality drops, and evaluate the performance of routes, providers, and codecs with precision. This enables true SLA enforcement and faster incident resolution.

If you’re looking to gain control over your call quality, explore Klearcom’s Voice Quality Testing to see how NVQA can fit into your infrastructure.

Setting Realistic MOS Targets

Not every environment can maintain a MOS above 4.3 at all times. But what matters is knowing your current baseline and understanding what your users need.

For internal business calls, targeting a high MOS score of 4.2 or higher is appropriate. For calls that rely on public networks or international carriers, aiming for a baseline of 3.8 is a practical goal.

Link these technical targets to real business outcomes. In contact centers, even a drop from 4.0 to 3.5 may coincide with longer handle times or increased repeat call volumes. Sales teams may find lower conversion rates when voice clarity drops below acceptable levels.

Making MOS part of your operational health reporting provides early warning signs and helps prioritize investments in network improvements or equipment upgrades.

Build MOS Monitoring into Your VoIP Strategy

VoIP quality metrics like MOS offer a simple but powerful way to measure what users hear. As global telecom infrastructures grow more complex, maintaining quality of service (QoS) requires a more active approach.

By embedding MOS into your monitoring strategy, you ensure that the voice quality you deliver matches what your users expect. You also gain the ability to isolate weak points, whether they stem from the network, the carrier, or the endpoint.

Klearcom’s NVQA platform is purpose-built for global teams seeking accurate, real-time insights without complex integrations. Whether you're launching new numbers, validating providers, or resolving incidents, having MOS data on hand changes the conversation.

Make MOS Your VoIP Baseline

If you are serious about improving call quality and protecting customer satisfaction, MOS needs to be at the heart of your monitoring practices. It remains the most important number for evaluating voice experience across modern networks.

With Klearcom's NVQA, telecom leaders can measure the actual experience of their users, not just synthetic test calls. This proactive capability reduces downtime, improves issue resolution, and safeguards customer trust.