Use of Interval Classes
The concept of interval class accounts for octave, enharmonic, and inversional equivalency. Consider, for instance, the following passage:
(To hear a MIDI realization, click the following: 106 KB
In the example above, all four labeled pitch-pairs, or dyads, share a common "intervallic color." In atonal theory, this similarity is denoted by interval class—ic 5, in this case. Tonal theory, however, classifies the four intervals differently: interval 1 as perfect fifth; 2, perfect twelfth; 3, diminished sixth; and 4, perfect fourth. Thus we see that in a dodecaphonic (i.e., chromatic) context, terminology tailored for the analysis of heptatonic (i.e., diatonic) music is often no longer suitable.
Incidentally, the example's pitch collection forms an octatonic set.
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