A JavaScript music theory framework.
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Teoria.js is a lightweight and fast JavaScript framework for music theory, both Jazz and Classical. It aims at providing an intuitive programming interface for music software (such as Sheet Readers, Sheet Writers, MIDI Players etc.).


  • A note object (teoria.note), which understands alterations, octaves, keynumber, frequency and etc. and Helmholtz notation

  • A chord object (teoria.chord), which understands everything from simple major/minor chords to advanced Jazz chords (Ab#5b9, F(#11) and such)

  • A scale object (teoria.scale), The scale object is a powerful presentation of a scale, which support quite a few handy methods. A scale can either be constructed from the predefined scales, which by default contains the 7 modes (Ionian, Dorian, Phrygian etc.) a major and minor pentatonic and the harmonic chromatic scale or from a arbitary array of intervals. The scale object also supports solfège, which makes it perfect for tutorials on sight reading.

  • An interval object (teoria.interval), which makes it easy to find the interval between to notes, or find a note which is a given interval from a note. There's also support for counting the interval span in semitones and inverting the interval.


Building the library is simple. Just fetch the code:

git clone git://github.com/saebekassebil/teoria

Install Jake (the build tool)

npm install -g jake

Enter the directory, and install the dependencies:

cd teoria && npm install

And build the library! You can build a minified version, by adding [minify] to the command:

jake build
# or
jake build[minify]


This is just a short introduction to what the framework can be used to. For a technical library reference, look further down this document.

// Create notes:
var a4 = teoria.note('a4');       // Scientific notation
var g5 = teoria.note("g''");      // Helmholtz notation
var c3 = teoria.note.fromKey(28); // From a piano key number

// Find and create notes based on intervals
teoria.interval(a4, g5);    // Returns a TeoriaInterval object representing a minor seventh
teoria.interval(a4, 'M6');  // Returns a TeoriaNote representing F#5
a4.interval('m3');          // Returns a TeoriaNote representing C#4
a4.interval(g5);            // Returns a TeoriaInterval object representing a minor seventh
a4.interval(teoria.note('bb5')).invert(); // Returns a TeoriaInterval representing a major seventh

// Create scales, based on notes.
a4.scale('mixolydian').simple();  // Returns: ["a", "b", "c#", "d", "e", "f#", "g"]
a4.scale('aeolian').simple();     // Returns: ["a", "b", "c", "d", "e", "f", "g"]
g5.scale('ionian').simple();      // Returns: ["g", "a", "b", "c", "d", "e", "f#"]
g5.scale('dorian');               // Returns a TeoriaScale object

// Create chords with the powerful chord parser
a4.chord('sus2').name;    // Returns the name of the chord: 'Asus2'
c3.chord('m').name;       // Reutns 'Cm'
teoria.chord('Ab#5b9');   // Returns a TeoriaChord object, representing a Ab#5b9 chord
g5.chord('dim');          // Returns a TeoriaChord object, representing a Gdim chord

// Calculate note frequencies or find the note corresponding to a frequency
teoria.note.fromFrequency(467); // Returns: {'note':{...},'cents':3.102831} -> A4# a little out of tune.
a4.fq(); // Outputs 440
g5.fq(); // Outputs 783.9908719634985

// teoria allows for crazy chaining:
teoria.note('a')    // Create a note, A3
  .scale('lydian')  // Create a lydian scale with that note as root (A lydian)
  .interval('M2')   // Transpose the whole scale a major second up (B lydian)
  .get('third')     // Get the third note of the scale (D#4)
  .chord('maj9')    // Create a maj9 chord with that note as root (D#maj9)
  .toString();      // Make a string representation: 'D#maj9'


TeoriaNote(name[, duration])

  • This function construct a teoria.note object.

name - The name argument is the note name as a string. The note can both be expressed in scientific and Helmholtz notation. Some examples of valid note names: Eb4, C#,,, C4, d#'', Ab2

duration - The duration argument is an optional object argument. The object has two also optional parameters:

  • value - A number corresponding to the value of the duration, such that: 1 = whole, 2 = half (minim), 4 = quarter, 8 = eight

  • dots - The number of dots attached to the note. Defaults to 0.

teoria.note (TeoriaNote)

The teoria.note object is teoria's interpretation and representation of a musical note. When calling teoria.note you're actually instantiating a TeoriaNote object.


A static method that returns an instance of TeoriaNote set to the note at the given piano key


A static method returns an object containing two elements:

note - A TeoriaNote which corresponds to the closest note with the given frequency

cents - A number value of how many cents the note is out of tune


  • Returns an instance of TeoriaNote set to the corresponding MIDI note value.

note - A number ranging from 0-127 representing a MIDI note value


  • The name of the note, in lowercase letter (only the name, not the accidental signs)


  • The numeric value of the octave of the note


  • The duration object as described in the constructor for TeoriaNote


  • An object containing two elements:

sign - The string symbolic of the accidental sign #, x, b or bb

value - The numeric value (mostly used internally) of the sign: # = 1, x = 2, b = -1, bb = -2


  • Returns the piano key number. Fx A4 would return 49

whitenotes - If this parameter is set to true only the white keys will be counted when finding the key number. This is mostly for internal use.


  • Calculates and returns the frequency of the note.

concertPitch - If supplied this number will be used instead of the normal concert pitch which is 440hz. This is useful for some classical music.


  • Returns an instance of TeoriaScale, with the tonic/root set to this note.

scaleName - The name of the scale to be returned. 'minor', 'chromatic', 'ionian' and others are valid scale names.

TeoriaNote#interval(interval[, direction])

  • A sugar function for calling teoria.interval(interval, direction)

Look at the documentation for teoria.interval

TeoriaNote#transpose(interval[, direction])

  • Like the #interval method, but changes this note, instead of returning a new


  • Returns an instance of TeoriaChord, with root note set to this note

name - The name attribute is the last part of the chord symbol. Examples: 'm7', '#5b9', 'major'. If the name parameter isn't set, a standard major chord will be returned.


  • Returns the note name formatted in helmholtz notation.

Example: teoria.note('A5').helmholtz() -> "a''"


  • Returns the note name formatted in scientific notation.

Example: teoria.note("ab'").scientific() -> "Ab4"


  • Returns all notes that are enharmonic with the note

Example: teoria.note('C').enharmonics() -> [teoria.note('Dbb'), teoria.note('b#')]

TeoriaNote#durationInSeconds(bpm, beatUnit)

  • Returns the duration of the note, given a tempo (in bpm) and a beat unit (the lower numeral of the time signature)

TeoriaNote#solfege(scale, showOctaves)

  • Returns the solfege step in the given scale context

scale - An instance of TeoriaScale, which is the context of the solfege step measuring

showOctaves - A boolean. If set to true, a "Helmholtz-like" notation will be used if there's bigger intervals than an octave


  • Returns the duration name.

Examples: teoria.note('A', 8).durationName() -> 'eighth', teoria.note('C', 16).durationName() -> 'sixteenth'


  • Returns this note's degree in a given scale (TeoriaScale). For example a D in a C major scale will return 2 as it is the second degree of that scale. If however the note isn't a part of the scale, the degree returned will be 0, meaning that the degree doesn't exists. This allows this method to be both a scale degree index finder and a "isNoteInScale" method.

scale - An instance of TeoriaScale which is the context of the degree measuring


  • Usability function for returning the note as a string

dontShow - If set to true the octave will not be included in the returned string.

TeoriaChord(root, chord)

  • A chord class with a lot of functionality to alter and analyze the chord.

root - A TeoriaNote instance which is to be the root of the chord

chord - A string containing the chord symbol. This can be anything from simple chords, to super-advanced jazz chords thanks to the detailed and robust chord parser engine. Example values: 'm', 'm7', '#5b9', '9sus4 and '#11b5#9'

teoria.chord(name || note[, octave || symbol])

  • A simple function for getting the notes, no matter the octave, in a chord

name - A string containing the full chord symbol, with note name. Examples: 'Ab7', 'F#(#11b5)'

note - Instead of supplying a string containing the full chord symbol, one can pass a TeoriaNote object instead. The note will be considered root in the new chord object

octave - If the first argument of the function is a chord name (typeof "string"), then the second argument is an optional octave number (typeof "number") of the root.

symbol - A string containing the chord symbol (exluding the note name)


  • Holds the full chord symbol, inclusive the root name


  • Holds the TeoriaNote that is the root of the chord


  • An array of notes that the chords is built of


  • A string which holds the quality of the chord, 'major', 'minor', 'augmented' or 'diminished'


  • Returns the note at a given interval in the chord, if it exists.

interval - A string name of an interval, for example 'third', 'fifth', 'ninth'.


  • Returns the naïvely chosen dominant which is a perfect fifth away.

additional - Additional chord extension, for example: 'b9' or '#5'


  • Returns the naïvely chosen subdominant which is a perfecth fourth away.

additional - Like the dominant's.


  • Returns the parallel chord for major and minor triads

additional - Like the dominant's


  • Returns the type of the chord: 'dyad', 'triad', 'trichord', 'tetrad' or 'unknown'.

TeoriaChord#interval(interval[, direction)

  • Returns the same chord, a interval away

TeoriaChord#transpose(interval[, direction])

  • Like the #interval method, except it's this chord that gets changed instead of returning a new chord.


  • Simple usability function which is an alias for TeoriaChord.name

TeoriaScale(tonic, scale)

  • The teoria representation of a scale, with a given tonic.

tonic - A TeoriaNote which is to be the tonic of the scale

scale - Can either be a name of a scale (string), or an array of absolute intervals that defines the scale. The default supported scales are:

  • major
  • minor
  • ionian (Alias for major)
  • dorian
  • phrygian
  • lydian
  • mixolydian
  • aeolian (Alias for minor)
  • locrian
  • majorpentatonic
  • minorpentatonic
  • chromatic
  • harmonicchromatic (Alias for chromatic)

teoria.scale(tonic, scale)

  • Sugar function for constructing a new TeoriaScale object


  • An array of TeoriaNotes which is the scale's notes


  • The name of the scale (if available). Type string or undefined


  • The TeoriaNote which is the scale's tonic


  • Returns an Array of only the notes' names, not the full TeoriaNote objects.


  • Returns the type of the scale, depending on the number of notes. A scale of length x gives y:
    • 2 gives 'ditonic'
    • 3 gives 'tritonic'
    • 4 gives 'tetratonic'
    • 5 gives 'pentatonic'
    • 6 gives 'hexatonic',
    • 7 gives 'heptatonic',
    • 8 gives 'octatonic'


  • Returns the note at the given scale index

index - Can be a number referring to the scale step, or the name (string) og the scale step. Example 'first', 'second', 'fourth', 'seventh'.

TeoriaScale#solfege(index, showOctaves)

  • Returns the solfege name of the given scale step

index Same as TeoriaScale#get

showOctaves - A boolean meaning the same as showOctaves in TeoriaNote#solfege

teoria.interval(from, to[, direction])

  • A sugar function for the #from and #between methods of the same namespace and for creating TeoriaInterval objects.

from - Either a string, in "simple-format" or a TeoriaNote that is the root of the interval measuring. If a string is supplied, it's treated as an interval in simple format, and returns a TeoriaInterval object.

to - Either a string, which is a "simple-format" interval such as 'M2' for major second, and 'P5' for perfect fifth. More details on this format later. If it's a string the note which is the given interval (to) away from the note (from) is returned. If to is a TeoriaNote then an interval object is returned, which represents the interval between the two notes. For the format of this interval object, take a look at the #between method

direction - The direction of the interval (only relevant when to is a string). Can be 'up' or 'down', defaults to 'up'

teoria.interval.from(from, to[, direction])

  • Returns a note which lies a given interval away from a root note.

from - Same as above, the TeoriaNote which is the base of the measuring

to - A string as described above.

direction - The direction as described above.

teoria.interval.between(from, to)

  • Returns an interval object which represents the interval between two notes.

from and to are two TeoriaNotes which are the notes that the interval is measured from. For example if 'a' and 'c' are given, the resulting interval object would represent a minor third.

teoria.interval.between(teoria.note("a"), teoria.note("c'")) -> teoria.interval('m3')


  • Returns the inversion of the interval provided

simpleInterval - An interval represented in simple string form. Examples:

  • 'm3' = minor third
  • 'P4' = perfect fourth
  • 'A4' = augmented fifth
  • 'd7' = diminished seventh
  • 'M6' = major sixth.

'm' = minor, 'M' = major, 'A' = augmented and 'd' = diminished

TeoriaInterval(intervalNumber, quality[, direction])

  • A representation of a music interval


  • The interval number (A ninth = 9, A seventh = 7, fifteenth = 15)


  • The type of interval (mostly used internally)


  • The quality of the interval ('diminished', 'minor', 'perfect', 'major' or 'augmented')


  • The direction of the interval (defaults to 'up')


  • Returns the number of semitones the interval span.


  • Returns the simple part of the interval (as opposed to #compound). Example:
teoria.interval('M17').simple() === 'M3'
teoria.interval('m23').simple() === 'm2'
teoria.interval('P5').simple() === 'P5'


  • Returns the whole interval, compound or not.
teoria.interval('M17').compound() === 'M17'
teoria.interval('m23').compound() === 'm23'
teoria.interval('P5').compound() === 'P5'


  • Returns a boolean value, showing if the interval is a compound interval


  • Returns true if the supplied interval is equal to this interval


  • Returns true if the supplied interval is greater than this interval


  • Returns true if the supplied interval is smaller than this interval


  • Returns the inverted interval as a TeoriaInterval

TeoriaInterval#qualityValue() - internal

  • Returns the relative to default, value of the quality. Fx a teoria.interval('M6'), will have a relative quality value of 1, as all the intervals defaults to minor and perfect respectively.