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
Ghosts (Monolake album) Ghosts (Monolake album) Ghosts is the seventh album from German techno music producer, Monolake (also known as Robert Henke). It is the second part of what is claimed to be a trilogy of three albums, that began with Monolake's sixth album, "Silence." Although the album follows a primarily techno aesthetic, it also incorporates elements of drum n' bass, dubstep, and ambient music. Some of the sounds of this album are notable in that they were created by sampling recordings that included frequencies outside of the range of human hearing (above 20 kHz), and then transposed down into the audible range.