Beat

A regularly occurring pulse that can be heard or implied.

(1) When two periodic signals are less than 20 Hz or so apart in frequency, and if they are mixed together, the amplitude of the combined signals will fluctuate as they alternately reinforce and cancel each other. These amplitude fluctuations cause loudness fluctuations and are called beats. See also difference tone.

(2) In music, the sensation of a basic pulse from which all rhythm in the piece is derived. Beats are of three types: a downbeat is a strongly accented pulse, such as the first in the bar; an offbeat is any pulse other than the downbeat; an upbeat, also called the anacrusis, is a special case of offbeat which immediately precedes the first beat of the bar, and hence the bar line.

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