The hypersonic effect is a phenomenon reported in a controversial scientific study by Tsutomu Oohashi et al.,[3] which claims that, although humans cannot consciously hear ultrasound (sounds at frequencies above approximately 20 kHz),[4][5][6][7] the presence or absence of those frequencies has a measurable effect on their physiological and psychological reactions.
The subjects could not consciously tell the difference, but when played music with the HFCs they showed differences measured in two ways: No effect was detected on listeners in the study when only the ultrasonic [14](frequencies higher than 24 kHz) portion of the test material was played for test subjects; the demonstrated effect was only present when comparing full-bandwidth to bandwidth-limited material.
[15] The 2006 study also investigated the comfortable listening level (CLL) of music with and without HFCs, an alternative way of measuring subject response to the sound.
[12][16] 480 man-hours of listening tests conducted at the London AES convention in 1980 by Laurie Finchman of KEF concluded that subjects could not distinguish a 20 kHz band limited version of a test signal from the original played back on equipment capable of reproducing sound up to 40 kHz.
[18] In September 2007, two members of the Boston Audio Society and the Audio Engineering Society published their study in which about half of the 554 double-blind ABX test listening trials made by 60 respondents showed the correct identification of high-resolution or CD-standard sampling rate.