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What is the difference between sound and noise?

It is important to recognise there is a significant difference between sound and noise. Sound is something that we hear in general. Noise is something that we can hear, but don’t necessarily want to hear. Noise is more dependent on character than decibel level. Two sounds can have the same energy level, but where one is acceptable, the other may be considered unreasonable due to different characteristics. When there is a high overall dose of sound, as is found close to the A1M, smaller increases lead to more noticeable change.

A generally accepted view is that a 3dBA increase will make the change noticeable.

If however, the character of the noise also changes due to a shift in the spectrum or pitch of the noise then this may be noticeable following a smaller change. In areas where there is already a fairly high level of noise, change can also be more noticeable.

Guidance and research, both in the UK and internationally, regarding transport sources of noise are directed at decibel change and not changes in the character of the noise.