Pitch interval

In musical set theory, a pitch interval (PI or ip) is the number of semitones that separates one pitch from another, upward or downward. In musical set theory, a pitch interval (PI or ip) is the number of semitones that separates one pitch from another, upward or downward. They are notated as follows: For example C4 to D♯4 Play (help·info) is 3 semitones: While C4 to D♯5 Play (help·info) is 15 semitones: However, under octave equivalence these are the same pitches (D♯4 & D♯5, Play (help·info)), thus the #Pitch-interval class may be used. In musical set theory, a pitch-interval class (PIC, also ordered pitch class interval and directed pitch class interval) is a pitch interval modulo twelve.