Similarity relation (music)
In music, a similarity relation or pitch-class similarity is a comparison between sets of the same cardinality, based upon shared pitch class and/or interval class content.
Allen Forte originally designated four types: Rp, R0, R1, and R2. In Rp one pitch class is different, in R0 all are different, and in R1 and R2 four interval classes are the same.
Rp is defined for sets S1 and S2 of cardinal number n and S3 of cardinal number n-1 as:
Meaning that S1 and S2 each have all the pitch-classes of S3, plus one.
