Audio Noise Level
Understand background noise level measurement in VoIP calls — how CallMeter measures ambient noise during silence, and what high noise floors mean for call intelligibility.
Audio Noise Level measures the background noise in an audio stream during non-speech moments, expressed in dBov (decibels relative to digital overload). While Audio Signal Level captures how loud the speech is, Noise Level captures everything else — ambient room noise, electrical hum, codec artifacts, and any other sound present when nobody is talking.
Think of it as measuring the "quiet" parts of the call. In a clean environment, those quiet parts should be truly quiet. In a noisy environment, the "silence" between words is filled with background sound that makes speech harder to understand.
How It Works
CallMeter uses Voice Activity Detection (VAD) to identify non-speech segments of the audio. During those segments, it computes the RMS power of the audio signal and converts it to dBov.
On the dBov scale:
- -60 to -70 dBov — Very quiet environment, minimal noise
- -40 to -50 dBov — Moderate noise, typical office or conference room
- -30 to -40 dBov — Noisy environment, impacts speech intelligibility
- Above -30 dBov — Severe noise, speech may be partially masked
Why It Matters
The gap between the speech signal level and the noise level determines intelligibility. This gap is known as the signal-to-noise ratio (SNR). Even if speech is loud enough, high background noise narrows the SNR and makes it harder for listeners to understand words clearly.
For enterprise VoIP testing, noise level measurement helps identify:
- Acoustic environment problems — Noise in the test environment leaking into measurements
- Codec or processing issues — Noise introduced by the audio processing chain itself
- Comfort noise behavior — Whether Comfort Noise Generation (CNG) is producing appropriate background fill during silence
- Echo residue — Imperfect echo cancellation leaving noise remnants
Common Causes of High Noise Levels
| Cause | Explanation |
|---|---|
| Noisy acoustic environment | Fans, HVAC, traffic, or open-plan office noise picked up by microphone |
| Poor microphone isolation | Omnidirectional microphone capturing ambient sound |
| Codec noise floor | Low-bitrate codecs or aggressive compression introducing quantization noise |
| CNG misconfiguration | Comfort Noise Generation producing noise louder than natural background |
| Echo cancellation residue | Residual echo mixed into the noise floor |
| Electrical interference | Ground loops or electromagnetic interference on analog audio paths |
How to Fix It
- Improve acoustic environment — Use directional microphones, acoustic treatment, or quieter test locations.
- Compare noise levels across endpoints — If one endpoint shows significantly higher noise, the problem is localized to that endpoint's environment or hardware.
- Check comfort noise settings — If noise appears only during silence periods and at a consistent level, it may be CNG. Verify that CNG level is appropriate.
- Test with a reference signal — Use a known-clean audio file to isolate whether noise is introduced by the endpoint, the network path, or the remote side.
- Evaluate codec choice — Some codecs perform better at low bitrates. Compare noise levels between codec configurations to find the optimal setting.
Related Metrics
- Audio Signal Level — Speech-only RMS level; compare with noise to assess SNR
- Audio Level RMS — Overall level including both speech and noise
- Comfort Noise Rate — Comfort noise insertion count during silence periods
- Speech Activity (VAD) — How much of the call is speech vs silence
Audio Signal Level
Understand audio signal level measurement in VoIP calls — how CallMeter detects speech volume using VAD-gated RMS levels, and what abnormal levels mean for call quality.
Speech Activity (VAD)
Understand the Voice Activity Detection speech ratio metric — how CallMeter measures the percentage of active speech in audio streams, and what it reveals about DTX and conversation patterns.