WOLFTONE
Wolf tone
A wolf tone, or simply a "wolf", is produced when a played note matches the natural resonating frequency of the body of a musical instrument, producing a sustaining sympathetic artificial overtone that amplifies and expands the frequencies of the original note, frequently accompanied by an oscillating beating which may be likened to the howling of the animal. A similar phenomenon is the beating produced by a wolf interval, which is usually the interval between E and G of the various non-circulating temperaments.The above text is a snippet from Wikipedia: Wolf tone
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