Ultrasound independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA). This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). Ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000
Bitcrusher the consequence that it is impossible to accurately record all frequencies right up to the Nyquist limit for a given sample rate. The solution is to increase the sample rate by an amount that accommodates the transition bands of the filters used both for sampling and for continuous-wave reconstruction; this is why, for example, Compact Discs use a sampling rate of 44.1 kHz to record audio that seldom exceeds 20 kHz, even though the Nyquist limit for this sample rate is 22.05 kHz. Another consideration is that for perfect reconstruction, the samples should be rendered as ideal impulses of infinitesimal