Introduction Noise and vibration are an omnipresent part of human existence and, although individual sensitivity to noise varies considerably, there are statistically derived thresholds for discomfort, annoyance, interference to speech intelligibility and hearing damage that are widely accepted. Noise is generated across a wide range of frequencies, ranging from very low frequency bass notes through to high frequency sound which is not audible to humans but can be heard by other animals such as dogs and bats. In fact the human auditory system typically responds to frequencies in the range of 20-20,000Hz, although the response is not linear and tends to deteriorate at the top end, particularly with age.