Understanding VoIP MOS and Voice Quality

Voice over IP calls travel across data networks, and their quality depends on how well those networks carry small, time-sensitive packets of audio. When quality drops, callers hear choppy audio, delays or silence. Measuring quality helps identify where problems come from.

What MOS means

The Mean Opinion Score (MOS) is a scale, usually from 1 to 5, that represents how good a call sounds to a listener. It was originally based on panels of people rating calls. In VoIP systems, MOS is normally estimated from network measurements rather than asked of real listeners.

Typical interpretation

• Around 4 and above — generally good quality
• Between about 3.5 and 4 — acceptable, with occasional noticeable issues
• Below about 3.5 — callers are likely to notice problems

These are guides, not strict thresholds. Different equipment and codecs behave differently.

What affects quality

• Packet loss — pieces of audio that never arrive
• Jitter — variation in arrival times, causing uneven audio
• Latency — delay between speaking and being heard
• Codec choice — how audio is compressed

Using quality data well

A single poor call rarely means much. Look for patterns: specific sites, times of day, network connections or devices. A cluster of low scores from one office during busy hours often points to local bandwidth contention.

Limits

Quality measurements are only as good as the data the phone system provides. Where a PBX does not report the necessary information, quality cannot be measured reliably and should not be guessed.

NOVIQ PBX Insights includes voice quality information where the connected PBX provides suitable data. Ask during a demo what is available for your platform.