freqi

Freqi

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

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Features

This package aims to:

• Provide a simple API for creating sets of frequencies
• Return actual sonic frequencies in Hz or relative frequencies for use with audio files
• Return a set of frequencies of any length
• Allow for any number of semitones per octave
• Handle bad data

What it doesn't do:

• Does not allow for input of notes as letters
• Does not allow for input of chords by name

Demo

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

Getting Started

It is recommended you install via Yarn or NPM

using

yarn add freqi

or

npm install freqi

Freqi is configured to work with both AMD and CJS applications.

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

import (ES6), like so

import freqi from 'freqi'

or for CommonJS use var freqi = require('freqi');

Usage

Freqi provides a pure function, getFreqs, which accepts a config object and returns an array of frequencies. There are two mandatory properties: startFreq and intervals.

startFreq can be a frequency in Hz, such as 440 (for 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. 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].

Optionally, 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 e.g. {intervals: [0, 3, 5, 7, 10], inversionStartNote: 2} is the equivalent of {intervals: [5, 7, 10, 12, 15], inversionStartNote: 2}. Note that the intervals array is automatically extended to the next octave to ensure the same number of notes are created.

Following on from the above, a larger 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.

If, for any reason, you want an even longer set of frequencies back simply use the repeatMultiple property, which will repeat the duplication process x number of times.

Mandatory properties:

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

Optional properties

• numSemitones : [number]
• rootNote : [number]
• inversionStartNote : [number];

Auxiliary properties

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

Plans

In a later version it will be possible to generate musical scales that use just intonation rather than equal temperament

Also, it will be possible to pass in note letters, such as C#