The impression of tension or clash experienced by a listener when certain combinations of tones are sounded together. Dissonance is subjective to the extent that different cultures perceive it differently, but in general it is known that certain combinations of notes produce it more than others, and it’s tied to the mathematical relationship the frequencies have with each other and how much beating occurs when the notes are sounded simultaneously. Although the harmonies that create dissonance may not be considered as pleasing to the ear by most listeners, dissonance occurs throughout music and can be used to great effect. Horror film soundtracks (take the screeching violins in the classic shower scene from the movie ‘Psycho’, for instance) are great places to find examples of dissonance.