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Sound at frequencies above the audible range, namely above 20 kHz, audible only to various non-human species. Because of its very short WAVELENGTH in the megahertz range, ultrasound is used as a safe alternative to X-ray photography in medical diagnosis. Ultrasound scanning is sometimes called sonography.
When a system with a natural vibrating FREQUENCY is stimulated by an outside force of the same frequency, the system can be set in a motion called VIBRATION. As the frequency of the stimulus closely approaches that of the system, OSCILLATION occurs, which reaches a maximum AMPLITUDE at the natural resonant frequency.
The subjective impression of FREQUENCY, in the same sense that LOUDNESS is the subjective sense of the INTENSITY or AMPLITUDE of a sound. As such, pitch is a psychoacoustic variable, and the degree of sensitivity shown to it varies widely with people. Some individuals have a sense of remembered pitch, that is, a pitch once heard can be remembered and compared to others for some length of time; others have a sense of absolute pitch called PERFECT PITCH.
The adjustment of the FREQUENCY of strings or pipes of musical instruments to conform to a given SCALE, or the adjustment of other instruments to such a tuned instrument.