Technical knowledge
Ambient, residual and specific noise: what is the difference?
The three concepts are related but not interchangeable. A technically valid comparison requires representative and comparable periods, source conditions and surrounding sound environment.
The three concepts are related but not interchangeable. A technically valid comparison requires representative and comparable periods, source conditions and surrounding sound environment.
Ambient noise
- It is the total noise present at a place and time, including the source under assessment and all other sources.
- It may vary with traffic, human activity, weather, animals and occasional events.
- Its characterisation should represent the period and condition of interest.
Residual noise
- It is characterised without the specific source under assessment, under the defined study conditions.
- It does not mean silence: all other sources remain.
- It should be as comparable as possible in period, weather and context.
Specific noise
- It is the contribution associated with the specific source and may be derived from the energy difference between ambient and residual levels where conditions allow.
- When the levels are close, uncertainty increases and separation may be less robust.
- Shutdowns, operating cycles or near-source measurements may support interpretation.
Representativeness and observations
- Short measurements may be unsuitable for variable sources.
- Unrelated events should be logged and treated with justification.
- Tonal or impulsive analysis depends on the relevant signal and applicable rules.
- The report should explain how periods were selected and compared.
This content is informative. Methods, criteria and framework should be defined for each specific case.