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Sound is a phenomenon in which pressure disturbances propagate through an elastic material medium. In the context of physics, it is characterised as a mechanical wave of pressure or related quantities, whereas in physiological-psychological contexts it refers to the reception of such waves and their perception by the brain. Though sensitivity to sound varies among all organisms, the human ear is sensitive to frequencies ranging from 20 Hz to 20 kHz. Examples of the significance and application of sound include music, medical imaging techniques, oral language and parts of science.