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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.
Any quantity or body is in a state of oscillation when its value or motion is continually changing so that it passes through maximum and minimum values or positions. When a system, body or quantity is set in PERIODIC motion or vibration, it is said to be in oscillation.
A form of STEREOPHONIC or multi-channel reproduction in which the sound source is spread around the listener by the use of four tracks or CHANNELs in recording or transmission and the use of four (or more) LOUDSPEAKERs. Conventional music or speech may be recorded in this way, in which case the speakers behind the listener add REVERBERATION to the original sound or are simply out of PHASE with respect to the front ones; or new works may be composed in which all tracks carry original material.
Also called flanging or flangeing. An effect created by adding together two identical SIGNALs separated by a very short time delay (less than 25 ms, but strongest below 10 ms). These short delays are within the audio WAVELENGTH range, and the combination of the two signals affects the frequency SPECTRUM of the composite sound.