For convenience, the guidelines are given in terms of external noise levels. It should be noted, however, that these are based largely on standards within buildings, since this is where the main activities which are affected by noise occur.
Noises from different sources are measured in different ways and alternatives are often available, even for one type of noise. In each case, the noise scales chosen provide the best measure of how people are affected. All environmental noise is measured using the A-weighted sound level - dB(A). The following descriptors take the variability of the noise and the response of the community into account: