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Music theory for JavaScript


Teoria.js is a lightweight and fast JavaScript library 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, key number, 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 supports 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 an arbitrary 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 two notes, or find a note that is a given interval from a note. There's also support for counting the interval span in semitones and inverting the interval.


$ npm install teoria

Can be used with both Node and Browserify/webpack/etc.

... or less preferable

Include the bundled build file, teoria.js from this repository, directly:

<script src="path/to/teoria.js"></script>


This is just a short introduction to what teoria-code looks like, 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 Interval object representing a minor seventh 
teoria.interval(a4, 'M6');  // Returns a Note representing F#5 
a4.interval('m3');          // Returns a Note representing C#4 
a4.interval(g5);            // Returns a Interval object representing a minor seventh 
a4.interval(teoria.note('bb5')).invert(); // Returns a Interval 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 Scale object 
// Create chords with the powerful chord parser 
a4.chord('sus2').name;    // Returns the name of the chord: 'Asus2' 
c3.chord('m').name;       // Returns 'Cm' 
teoria.chord('Ab#5b9');   // Returns a Chord object, representing a Ab#5b9 chord 
g5.chord('dim');          // Returns a Chord 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' 


teoria.note (name | coord[, duration])

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

coord - If the first argument isn't a string, but a coord array, it will instantiate a Note instance.

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.


A static method that returns an instance of Note set to the note at the given piano key, where A0 is key number 1. See Wikipedia's piano key article for more information.


A static method returns an object containing two elements:

note - A Note 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 Note set to the corresponding MIDI note value.

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


  • Returns an instance of Note representing the note name

note - 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

  • 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 Note


  • Returns the string symbolic of the accidental sign (x, #, b or bb)


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


  • Returns the piano key number. E.g. 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.


  • Returns a number ranging from 0-127 representing a MIDI note value


  • 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 the pitch class (index) of the note.

This allows for easy enharmonic checking:

teoria.note('e').chroma() === teoria.note('fb').chroma();

The chroma number is ranging from pitch class C which is 0 to 11 which is B


  • Returns an instance of Scale, 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.


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

Look at the documentation for teoria.interval


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


  • Returns an instance of Chord, 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

oneAccidental - Boolean, if set to true, only enharmonic notes with one accidental is returned. E.g. results such as 'eb' and 'c#' but not 'ebb' and 'cx'

// -> 'dbb, b#' 
// -> 'b#' 

Note#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)

Note#solfege(scale, showOctaves)

  • Returns the solfege step in the given scale context

scale - An instance of Scale, 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 (Scale). 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 exist. This allows this method to be both a scale degree index finder and an "isNoteInScale" method.

scale - An instance of Scale 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.

Chord(root, chord)

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

root - A Note 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 Note 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 (excluding the note name)

  • Holds the full chord symbol, inclusive the root name.


  • Holds the Note that is the root of the chord.


  • Returns an array of Notes that the chord consists of.


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


  • Returns the bass note of the chord (The note voiced the lowest)


  • Works both as a setter and getter. If no parameter is supplied the current voicing is returned as an array of Intervals

voicing - An optional array of intervals in simple-format that represents the current voicing of the chord.

Here's an example:

var bbmaj = teoria.chord('Bbmaj7');
// Default voicing: 
bbmaj.voicing();  // #-> ['P1', 'M3', 'P5', 'M7']; 
bbmaj.notes();    // #-> ['bb', 'd', 'f', 'a']; 
// New voicing 
bbmaj.voicing(['P1', 'P5', 'M7', 'M10']);
bbmaj.notes();    // #-> ['bb', 'f', 'a', 'd']; 

NB: Note that above returned results are pseudo-results, as they will be returned wrapped in Interval and Note objects.


  • Returns a string which holds the quality of the chord, 'major', 'minor', 'augmented', 'diminished', 'half-diminished', 'dominant' or undefined


  • 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 perfect 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'.


  • Returns the same chord, a interval away


  • 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

Scale(tonic, scale)

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

tonic - A Note 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 scales supported by default are:

  • major
  • minor
  • ionian (Alias for major)
  • dorian
  • phrygian
  • lydian
  • mixolydian
  • aeolian (Alias for minor)
  • locrian
  • majorpentatonic
  • minorpentatonic
  • chromatic
  • harmonicchromatic (Alias for chromatic)
  • blues
  • doubleharmonic
  • flamenco
  • harmonicminor
  • melodicminor
  • wholetone

teoria.scale(tonic, scale)

  • Sugar function for constructing a new Scale object


  • An array of all the scale ID's that comes with teoria


  • Returns an array of Notes which is the scale's notes

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


  • The Note which is the scale's tonic


  • Returns an array of Notes which is the scale's notes


  • Returns an Array of only the notes' names, not the full Note 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) of the scale step. E.g. 'first', 'second', 'fourth', 'seventh'.

Scale#solfege(index, showOctaves)

  • Returns the solfege name of the given scale step

index Same as Scale#get

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

teoria.interval(from, to)

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

teoria.interval(string: from)

  • A sugar method for the Interval.toCoord function

teoria.interval(Note: from, string: to)

  • A sugar method for the Interval.from function

teoria.interval(Note: from, Interval: to)

  • Like above, but with a Interval instead of a string representation of the interval

teoria.interval(Note: from, Note: to)

  • A sugar method for the Interval.between function
teoria.interval.from -> Interval.from
teoria.interval.between -> Interval.between
teoria.interval.invert -> Interval.invert
teoria.interval.toCoord -> Interval.toCoord


  • A representation of a music interval


  • Returns a Interval representing the interval expressed in string form.

Interval.from(from, to)

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

from - The Note which is the root of the measuring

to - A Interval

Interval.between(from, to)

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

from and to are two Notes 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.

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

The number may be prefixed with a - to signify that its direction is down. E.g.:

m-3 means a descending minor third, and P-5 means a descending perfect fifth.


  • The interval representation of the interval


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


  • The value of the interval - That is a ninth = 9, but a downwards ninth is = -9


  • Returns the simpleInterval representation of the interval. E.g. 'P5', 'M3', 'A9', etc.


  • Returns the name of the simple interval (not compound)


  • Returns the type of array, either 'perfect' (1, 4, 5, 8) or 'minor' (2, 3, 6, 7)


  • The quality of the interval ('dd', 'd' 'm', 'P', 'M', 'A' or 'AA')

verbose is set to a truish value, then long quality names are returned: 'doubly diminished', 'diminished', 'minor', etc.


  • The direction of the interval

dir - If supplied, then the interval's direction is to the newDirection which is either 'up' or 'down'


  • Returns the number of semitones the interval span.


  • Returns the simple part of the interval as a Interval. Example:

ignoreDirection - An optional boolean that, if set to true, returns the "direction-agnostic" interval. That is the interval with a positive number.

teoria.interval('M17').simple();    // #-> 'M3' 
teoria.interval('m23').simple();    // #-> 'm2' 
teoria.interval('P5').simple();     // #-> 'P5' 
teoria.interval('P-4').simple();    // #-> 'P-4' 
// With ignoreDirection = true 
teoria.interval('M3').simple(true);     // #->'M3' 
teoria.interval('m-10').simple(true);   // #-> 'm3' 

NB: Note that above returned results are pseudo-results, as they will be returned wrapped in Interval objects.


  • Returns the number of compound intervals


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


  • Adds the interval to this interval, and returns a Interval representing the result of the addition


  • 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 Interval

Interval#qualityValue() - internal

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