Wolf tone

A wolf tone, wolf note, or simply a "wolf", is an undesirable phenomenon that occurs in some bowed-string musical instruments, most notoriously in the cello. It happens when the pitch, or more particularly the fundamental frequency, of the played note is close to a particularly strong natural resonant frequency of the vibration of the instrument's body. Wind instruments can produce a similar effect for similar reasons—notably, in the case of brass instruments, when the played note's pitch is near a resonant frequency of the instrument's bell.

A wolf note is hard for the player to control: instead of a solid note it tends to produce a thin "surface" sound, sometimes jumping to the octave of the intended note. In extreme cases, a "stuttering" or "warbling" sound is produced, as in the sound example given below. This sound may be likened to the howling of a wolf. A somewhat similar sound is the beating produced by a wolf interval, which is usually the interval between E♭ and G♯ of the various non-circulating temperaments.