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intervals 
Difference in pitch between two successive notes (melodic interval) or simultaneous notes (harmonic interval).
octave
Interval of eight tones (e.g., from C to C).
sixth
Interval of six tones (e.g., from C to A).
fourth
Interval of four tones (e.g., from C to F).
second
Interval of two tones (e.g., from C to D).
seventh
Interval of seven tones (e.g., from C to B).
fifth
Interval of five tones (e.g., from C to G).
third
Interval of three tones (e.g., from C to E).
unison
Notes of the same pitch, or one or more octaves apart, produced simultaneously by several voices or instruments.
