Dissonance

Dissonance is a combination of pitches perceived as unstable or tense within a musical context. Its effect depends on acoustic properties, musical style, and expectations.

Beating: A periodic fluctuation in sound amplitude produced when tones of nearby frequencies interfere. Nearby pitches can produce audible beats that contribute to roughness and tension.
Interval (music): The pitch distance between two notes, measured by their frequency relationship or musical spelling. Intervals provide the basic unit for describing two-note dissonances.
Consonance: A combination of pitches perceived as stable or restful in a musical context. Consonance is the perceptual counterpart against which musical dissonance is defined.
Pythagorean tuning: A tuning system that derives intervals from frequency ratios based on powers of three and two. Its simple ratios helped anchor ancient accounts of consonant and dissonant intervals.
Critical band: A frequency range within which sounds interact strongly in the auditory system. Tones within one critical band can mask or roughen each other more than widely separated tones.
Chord: A set of pitches sounded together or understood as a harmonic unit. Dissonance often describes how a chord behaves within a progression.
Tonal music: Music organized around a central pitch and a hierarchy of related tones and harmonies. Tonal music supplies expectations that make some intervals sound more tense than others.
Pythagoras: An ancient Greek philosopher associated with mathematical accounts of musical intervals. Pythagorean traditions connected judgments of musical tension to numerical frequency ratios.
Roughness: A sensation of rapid amplitude fluctuation caused by interacting sound components. Roughness offers an acoustic account of why some simultaneous tones sound harsh.
Tritone: An interval spanning three whole tones, commonly spelled as an augmented fourth or diminished fifth. The tritone is a familiar interval whose tension varies with musical context.

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