Tri-tone

Tri-tone

In music theory, the tritone is strictly defined as a musical interval composed of three adjacent whole tones. For instance, the interval from F up to the B above it (in short, F–B) is a tritone as it can be decomposed into the three adjacent whole tones F–G, G–A, and A–B. According to this definition, within a diatonic scale there is only one tritone for each octave. For instance, the above-mentioned interval F–B is the only tritone which can be formed using the notes of the C-major scale. A tritone is also commonly defined as an interval spanning six semitones. According to this definition, a diatonic scale contains two tritones for each octave. For instance, the above-mentioned C-major scale contains the tritones F–B (from F to the B above it, also called augmented fourth) and B-F (from B to the F above it, also called diminished fifth, semidiapente, or semitritonus). To avoid the ambiguity created by the existence of two different definitions, a tritone which meets the strict definition, such as F–B, is sometimes called a proper tritone.

In classical music, the tritone is a harmonic and melodic dissonance and is important in the study of musical harmony. "Any tendency for a tonality to emerge may be avoided by introducing a note three whole tones distant from the key note of that tonality." Contrastingly the tritone contained within the dominant seventh chord helps to establish the tonality.