Musical Intervals Table — Allen Forte Approach

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Ascending Semitones ↑ Descending Semitones ↓ Traditional Interval Interval Class (IC)
0 0 Unison / Perfect Octave IC0
1 11 Minor Second / Major Seventh IC1
2 10 Major Second / Minor Seventh IC2
3 9 Minor Third / Major Sixth IC3
4 8 Major Third / Minor Sixth IC4
5 7 Perfect Fourth / Perfect Fifth IC5
6 6 Tritone (Augmented Fourth / Diminished Fifth) IC6
7 5 Perfect Fifth / Perfect Fourth IC5
8 4 Minor Sixth / Major Third IC4
9 3 Major Sixth / Minor Third IC3
10 2 Minor Seventh / Major Second IC2
11 1 Major Seventh / Minor Second IC1
12 0 Perfect Octave IC0

Interval Class Summary Table

Interval Class Equivalent Semitones Traditional Intervals
IC0 0 Unison / Octave
IC1 1 / 11 Minor Second / Major Seventh
IC2 2 / 10 Major Second / Minor Seventh
IC3 3 / 9 Minor Third / Major Sixth
IC4 4 / 8 Major Third / Minor Sixth
IC5 5 / 7 Perfect Fourth / Perfect Fifth
IC6 6 Tritone
IC(n) = min(n, 12 - n)
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