Interval Class Calculator

Interval Class Calculator

Calculate pitch-class distance, interval class, inversion/complement, and Forte-style interval vectors for note pairs, chords, rows, and pitch-class sets.

🎼 Analysis Presets

Preset use: Load a real music-theory example, then adjust the note pair, octave handling, notation, and set text for your own analysis.

🎹 Pitch-Class Inputs
Pitch class 0 through 11 in 12-tone equal temperament.
The pair result uses this pitch against the first one.
Used only when octave-aware directed semitones are selected.
Middle C is commonly named C4 in many DAWs and tuners.
Interval class itself folds every interval into 0 through 6.
Enharmonic spellings share the same pitch class.
Standard Forte vectors use unique pitch classes.
Enter notes or integers separated by spaces or commas, for example C Eb F# A or 0 3 6 9.
Interval Class
IC 5
perfect fourth / perfect fifth class
Directed Interval
+7 st
ascending from C to G
Set Vector
<012111>
IC1 through IC6 pair counts
Set Pairs
6
unordered pitch-class pairs

Calculation Breakdown

📊 Analysis Spec Grid
C-G
Selected pair
5 st
Inversion or complement span
4 pcs
Parsed set cardinality
6 pairs
Vector pair total
📐 Interval Class Reference
Interval ClassSemitone ContentCommon Interval NamesExample From C
IC00 or 12Unison, octave, repeated pitch classC to C
IC11 or 11Minor second, major seventhC to Db or B
IC22 or 10Major second, minor seventhC to D or Bb
IC33 or 9Minor third, major sixthC to Eb or A
IC44 or 8Major third, minor sixthC to E or Ab
IC55 or 7Perfect fourth, perfect fifthC to F or G
IC66Tritone, augmented fourth, diminished fifthC to F# or Gb
🔎 Common Set Vector Examples
Set TypePitch ClassesInterval VectorReading
Major or minor triad0, 4, 7 or 0, 3, 7<001110>One each of IC3, IC4, and IC5
Dominant seventh0, 4, 7, 10<012111>One tritone plus two third-class intervals
Diminished seventh0, 3, 6, 9<004002>Four IC3s and two tritones
Whole-tone hexachord0, 2, 4, 6, 8, 10<060603>Only even interval classes appear
Diatonic collection0, 2, 4, 5, 7, 9, 11<254361>Major scale pitch-class balance
🧮 Pair And Set Comparison
Analysis ModeWhat It MeasuresFormula BasisBest Use
Directed pitch-class intervalOrdered motion from first pitch class to second(B - A) mod 12Melodic contour, row intervals, ordered transformations
Interval classSmallest distance between two pitch classesmin(n, 12 - n)Forte analysis, inversion-equivalent comparison
Octave-aware semitonesActual register distance between two entered notes(octaveB - octaveA) x 12 + (B - A)Keyboard spacing, voicing span, transcription checks
Interval vectorCounts every unordered pair in a set by IC1 through IC6All i < j pairs, folded by interval classChord, scale, row segment, and set-class comparison
🎲 Preset Analysis Reference
PresetPairSet TextExpected Focus
Minor 2ndC to DbC DbIC1 semitone tension
TritoneC to F#C F#IC6 symmetry under inversion
Major TriadC to EC E G<001110> consonant triad profile
Dominant 7thC to BbC E G Bb<012111> with one tritone
Whole-Tone CellC to F#C D E F#Even-interval color with IC2 and IC4
Chromatic ClusterC to D#C C# D D#Dense IC1 and IC2 content
Set-theory tip: Interval class is inversion-equivalent. C to E and C to Ab both reduce to IC4 because 4 and 8 semitones fold to the same class.
Vector tip: A standard interval vector ignores note spelling, register, and order. Convert the passage to pitch classes first, then compare the six counts.

Music theory students often encounter confusion when they first learn about interval class in music theory students studies. An interval class refer to the distance between two notes. However, the interval class remains the same irrespective of the ascending or descending distance between those two notes.

By learning about interval class, music theory students learn to think about music in a different way. The interval class calculator present musical results for the entered pitch classes. This calculator allow music theory students to focus on the musicality of the intervals rather than the mathematics behind these intervals.

What are interval classes and interval vectors?

The interval class calculator work because each interval class reduces the distance between two notes to a number between zero and six. For instance, both the ascending major third and the descending minor sixth reduces to interval class four. Thus, each of these two intervals are of the same interval class.

This reduction of intervals into a common interval class reflect the way a listener hear intervals when they are inverted. For instance, moving up a third and moving down a sixth in harmony will sound the same to a listener. The interval class calculator provides both the directed interval and the interval class so that music theory students can study both representations of these relationships in music theory.

Interval vectors extend the concept of interval classes to sets of musical notes. Rather than asking how far one note is from the next, music theory examine how many pair of notes in a set belong to each interval class. Each set of notes has its own interval vector, which function as a musical fingerprint.

Two different set of notes can sound related to one another when they have the same interval vector. The interval class calculator calculates these vectors once the music theory student enters the set of notes into the calculator. The interval vector calculator determine whether to count repeated pitch class within that set or to treat the set as a collection of unique musical members.

This impacts the interval vector if the set includes unisons or octaves. The reference table on the page indicate the common name for each interval class. For instance, interval class five include perfect fourths and perfect fifths.

These intervals behave in a similar fashion because perfect fourths and perfect fifths is inversions of each other. Thus, perfect fourths and perfect fifths shares the same interval class. Interval class six is unique because a tritone do not have its own inverted interval.

Because there is no inversion for this interval class, it is special in both tonal and atonal music. A composer may use a tritone in music to indicate either more maximum tension or maximum symmetry in their composition. The interval class calculator allow music theory students to study the relationship between two chords that may seem unrelated on the page.

For instance, a dominant seventh chord and a half-diminished seventh chord has no relationship on the staff notation staff paper. However, there interval vectors may have similarities. By entering these two chords into the interval class calculator, music theory students can study how similar or different the two chords is.

A music theory student may use this instrument when transcribing music from a recording or arranging music for a performance. By entering the notes into the calculator, each in its appropriate octaves, the music theory student can use the octave-aware mode to see the actual span of the pitch classes. That information can be deselected to study the abstract concept of the interval classes of the studied music.

Many people believe that interval classes and interval vectors is used for studying post-tonal music. However, interval classes can describe tonal music as well. A ii-V-I chord progression will contain a different distribution of interval classes than a sequence of chromatic notes.

The interval vector for these examples can be compared to study the differences in the chord progressions. Not only can people compare the interval vector of two sections within a song, but they can study the interval vector of two different songs. The interval class calculator is valuable to music theory students because it performs the mathematics of music theory for them.

When music theory students no longer have to worry about the mathematics behind the intervals, they can focus on more important question of music theory. For instance, music theory students can study which interval classes are dominant in a chord progression. Another question is where the tritone notes appear in the studied chord or progression.

Furthermore, music theory students can study how the interval vector change with the addition or removal of a note from a chord progression. Such questions can help music theory students understand the effect of their musical ideas. The numbers may be of little importance to music theory students, but the musical relationships are of the most utmost importance.

Interval Class Calculator

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