Hypersonic effect

The hypersonic effect is a proposed response in which inaudible, ultrahigh-frequency sound components alter brain activity or the perceived quality of audible music.

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Auditory system: The sensory system that detects sound and processes it through the ear and brain. The hypothesis concerns changes in brain activity linked to sound, not just conscious hearing.
Tsutomu Oohashi: A Japanese researcher who studied physiological and perceptual responses to high-frequency sound. Oohashi and colleagues popularized the hypersonic-effect hypothesis through their experiments.
Ultrasound: Sound waves with frequencies above the upper limit of typical human hearing, about 20 kilohertz. The effect concerns ultrasonic components accompanying audible music.
Audio engineering: The design and operation of systems for recording, processing, mixing, and reproducing sound. Engineering choices determine whether ultrasonic components are captured and reproduced.
Auditory cortex: The brain regions that process auditory information, including sound features and patterns. Reported neural responses to high-frequency sound have been measured in auditory cortical regions.
Science (journal): A peer-reviewed scientific journal published by the American Association for the Advancement of Science. A 2000 report presenting evidence for the effect appeared in this journal.
Psychoacoustics: The study of how physical sound relates to hearing and auditory perception. The claimed change in musical quality is a perceptual question within this field.
Super Audio CD: A digital audio disc format that uses Direct Stream Digital encoding and supports high-frequency content. Its extended bandwidth has often been discussed alongside the hypersonic-effect claim.
Auditory evoked potential: An electrical brain response time-locked to an auditory stimulus. Evoked potentials are among the neural measures used to test responses to inaudible components.
High-resolution audio: Digital audio formats designed to represent frequencies or dynamic range beyond standard CD specifications. The hypothesis became relevant to claims about whether extended high-frequency audio has perceptual value.