1.6.3 • Public • Published


A javascript api for generating frequencies for use with the web audio API

Build Status Codacy Badge


This package aims to:

  • Provide a simple API for creating sets of frequencies from numeric intervals
  • Return actual sonic frequencies in Hz or relative frequencies for use with oscillator or audio file playback
  • Supports multiple tuning systems, both tempered and just
  • Allow for any number of semitones per octave (equal temperament mode only)
  • Return an array of frequencies of any length
  • Provide a way of creating frequencies from within the intervals themselves
  • Handle bad data

What it doesn't do:

  • Does not allow for input of notes as letters (yet)
  • Does not allow for input of chords by name
  • It is not a sequencer or audio processor


This module has no dependencies.

Getting Started

It is recommended you install via Yarn or NPM


yarn add freqi


npm install freqi

Freqi is configured to work with ESM, AMD and CJS applications.

If you're using Webpack or some other CJS module loader

import (ES6), like so

import freqi from 'freqi'

or for CommonJS loaders (such as Browserify) use var freqi = require('freqi');


Freqi provides a pure function, getFreqs, which accepts a config object and returns an array of frequencies. There is one mandatory property: intervals, though it is recommended that startFreq be set too.

intervals is the set of notes you want to generate frequencies from. These intervals can be any integer, positive or negative e.g. [-5, 0, 7] where 0 is the start frequency.

startFreq can be a frequency in Hz, such as 440 (for the note A) or a relative frequency such 1 which is useful for playing back audio files, such as MP3s or OGGs, where 1 is the original playback rate. 440 is the default value.

Tuning Systems

Freqi supports a wide range of tuning systems. By default it will use 12 tone equal temperament (12TET). To use 4TET for example, simply set numSemitones to 4. For Just Intonation tuning systems set the mode to one of the following:

  • pythagorean - Pythagorean just intonation excluding the syntonic comma
  • truePythag - Pythagorean just intonation that includes the syntonic/pyhthagorean comma
  • fiveLimit - A set of whole number ratios using only powers of 2, 3, or 5
  • diatonic - A justly-tuned major diatonic scale that uses the 5-limit system devised by Ptolemy
  • diatonicIndian - A justly-tuned diatonic scale that uses 27/16 for Dha
  • twentyTwoShrutis - A justly-tuned 22 note Indian scale described by the Bharata and Dattilam
  • gioseffoZarlino - An unusual justly tuned 16 note scale designed for one of Zarlino's harpsichords
  • majorPentatonic - A major pentatonic scale
  • egyptianSuspended - An Egyptian pentatonic scale otherwise known as suspended pentatonic
  • bluesMinorManGong - An ancient Chinese pentatonic scale
  • bluesMajorRitsusenYo - A five-note scale without semitones used in the Japanese shōmyō chant
  • minorPentatonic - A five-note minor pentatonic scale without semitones

Please note, once in one of these modes, other config params, such as numNotes, will have no effect as they are fixed scale tuning systems.

If your program needs to explicitly set equal temperament mode, use the key eqTemp.

For quick access to these keys a you can use the method freqiModes, which will retuen an array of the keys.

There is also a mode for the harmonic series called hSeries. In its raw state it may not particularly useful for making music, but may be of interest to music theorists. Unlike all other tuning systems it is not zero-based. It follows the scientific naming convention where 1 is the fundamental, 2 the 2nd harmonic and so on.

Meta data

An object containing meta data for use in your application can be accessed via tuningSystemsData. This includes the frequency ratios for each Just tuning system, short and long names plus long-form descriptions.

Optional Params

You can pass in a custom number of semitones. The default is 12, a western chromatic scale, but you could pass in 19 for a non-western scale - this can produce very interesting results!

If you are using Freqi to generate multiple sequences of notes you can offset the root note using the rootNote property. A value of 2 for example will pitch the provided intervals up by two semitones.

Also, you can offset the intervals themselves to produce inversions or rootless voicings. {intervals: [0, 3, 5, 7, 10], intervalStartIndex: 2} will create a set of frequencies from the 2nd index in the intervals array, so it's equivalent to {intervals: [5, 7, 10]. If you always want arrays of the same length use the numNotes property. If that is set Freqi will automatically produce the desired number of notes. Use this in conjunction with amountToAdd if you want it to extend the intervals by a certain number of semitones e.g. {intervals: [0, 3, 5, 7, 10], intervalStartIndex: 2, amountToAdd: 12, numNotes: 5} will yield

Following on from the above, by using numNotes, a larger or smaller number of notes can be set than is provided by the intervals property e.g. {intervals : [0, 3, 5], numNotes: 5}. In this case Freqi will add the missing array items and extend them to the next octave. You can have Freqi add any value to these missing items - setting amountToAdd to 0 will effectively add the same numbers again.

Mandatory properties:

  • intervals : [array] // e.g. [0, 3, 5]

Optional properties

  • startFreq : [number] // e.g. 440
  • numSemitones : [number] // e.g. 19
  • mode: [string] // justInt, pythagorean, truePythag, diatonic, fiveLimit, diatonicIndian, twentyTwoShrutis
  • rootNote : [number]
  • intervalStartIndex : [number]

Auxiliary properties

  • numNotes : [number];
  • amountToAdd : [number] // 12 if you want to go up an octave;
  • type : [string] // for debugging;


View the online demo on GitHub here

Or download/clone it and run npm install which will install any dependencies, npm run build to create the demo bundle and npm run start which will start a new server at localhost:8080. Then, be sure to navigate to the demo folder in order to see the page i.e. localhost:8080/demo

Release notes

1.6.0 Addition of pentatonic tuning systems. The getModes. method is deprecated in favour of the freqiModes property. The getMetaData method is deprecated in favour of the tuningSystemsData property.

1.5.3 Addition of meta data for each tuning system and getMetaData method

1.5.2 TypeScript definitions added

1.5.2 Native EcmaScript module support added

1.4.0 Bug fix for True Pythagorean

1.3.0 Support for true pythagorean scale added.

1.2.0 Support for Gioseffo Zarlino's 16 note scale added.

1.1.0 As described above, 1.1.0 supports mutliple tuning systems. The source has been refactored to TypeScript and test coverage has been improved.

1.0.0 included one breaking change whereby inversionStartNote was changed to intervalStartIndex to better express its purpose. If you're not explicitly using this property in your app you should be able to safely upgrade to the latest version.


The library is written in TypeScript. Rollup has been used as the bundler for two reaons:

  1. To ensure backwards compatibility - there's an issue with how TS publishes modules defined using the UMD IIFE
  2. The TypeScript compiler (still) doesn't support .mjs files as a target

The build script first runs the TS compiler to produce the type definitions, then the Rollup compiler to produce the library artefacts.

Mocha is used as the testing framework.

Browserify is used to build the demo.



npm run build creates the TS definitions and compiles the library using TS and Rollup respectively

npm run build:run will compile the lib, then the demo and then start the local server. Navigate to localhost:8080/demo to view it


  • Please post feature requets or sugestions as issues here:
  • As of version 1.6.0 all tuning system data is stored in the src/tuning-systems.json file. Any additional systems must be added here.
  • There is no need to create any additional equally tempered tuning systems in the core lib as the function getEqTempNote will allow for the division of an octave into any number of notes.
  • Based on annecdotal feedback, the most useful feature to develop next is support for note letters e.g. getFreqs(['A', 'C', 'D#']) or getFreqs(['Sa', 'Re', 'Ga'])

Package Sidebar


npm i freqi

Weekly Downloads






Unpacked Size

187 kB

Total Files


Last publish


  • rbultitude