Hypersonic effect Hypersonic effect The hypersonic effect is a term coined to describe a phenomenon reported in a controversial scientific study by Tsutomu Oohashi et al., which claims that, although humans cannot consciously hear ultrasound (sounds at frequencies above approximately 20 kHz), the presence or absence of those frequencies has a measurable effect on their physiological and psychological reactions. Numerous other studies have contradicted the portion of the results relating to the subjective reaction to high-frequency audio, finding that people who have "good ears" listening to Super Audio CDs and high resolution DVD-Audio recordings on high fidelity systems capable of reproducing sounds
Underwater acoustics 1 kHz and 30 kHz. At very high frequencies, above 100 kHz, thermal noise of water molecules begins to dominate. The thermal noise spectral level at 100 kHz is 25 dB re 1 μPa²/Hz. The spectral density of thermal noise increases by 20 dB per decade (approximately 6 dB per octave). Transient sound sources also contribute to ambient noise. These can include intermittent geological activity, such as earthquakes and underwater volcanoes, rainfall on the surface, and biological activity. Biological sources include cetaceans (especially blue, fin and sperm whales), certain types of fish, and snapping shrimp. Rain can produce high levels