Introduction

SynthJS is an interpreter and toolset for the Synth Web Audio Programming Language. Its core JavaScript parsing engine leverages the capabilities of the Web Audio API, allowing SynthJS to distill complex compositions, effects, and instruments into JSON-structured sequences.

Related applications

• Kebo is a React synthesizer based on SynthJS.
• SynthJS-Editor is a real-time SPA for writing and debugging Synth compositions.

Usage

Install:

npm install synth-javascript

Every instance of SynthJS handles a single instrument/voice. Pass each instance a voice configuration:

import SynthJS from 'synth-javascript'

const composition = new SynthJS({  
  tempo: 128,                // default is 60
  instrument: 'square',      // default is 'sine'
  timeSig: '3/4',            // default is '4/4'
  loop: true                 // default is false  
})

Write and play:

composition.update({notes: `
  t d4, t d_4,
  t d4, q a#5,
  q b5, q rest
`})

composition.play()

Note: Up to six audio contexts (voices) can be active on the window object. Each instance of SynthJS creates a new context.

Note duration

A note's duration is the amount of time it is played relative to the tempo, known as a subdivision. Common subdivisions are abbreviated as follows:

• z = zero (useful for slides where the end note is not held)
• ts = thirty-second
• s = sixteenth
• s. = dotted-sixteenth
• t = triplet
• e = eighth
• e. = dotted-eighth
• q = quarter
• q. = dotted-quarter
• h = half
• h. = dotted-half
• w = whole
• w. = dotted-whole
• i = indefinite (1,000 whole notes)

Note: 3 triplets = 2 eighths

Note names

A note's name is mapped to its frequency in hertz. D in the 5th octave is written as d5. Similarly, G-flat in the 3rd octave is g_3, and C-sharp in the 6th octave is c#6. A note may be between a0 and g#7, inclusive.

Basic notation

General format

h d5, q g_3, q c#6 [duration][space][note][comma]

Note: Any amount of tabs, newlines, or whitespace can appear after the comma, but one space must appear between the duration and pitch.

Repetition

To simplify the writing process, groups of notes may be assigned to variable names. Notice the use of colons and semicolons in this example:

motif: h d5, q g_3, q c#6;

t d4, motif,
t a4, motif

Repeated notes may be multiplied by an integer value.

h c4 * 8, t b_3 * 3

Chords

Use the + operator to play notes simultaneously. A chord is constituted of its pitches played for a specified duration.

chord: h d3 + a3 + g3;

h d3, chord,
h a3, chord

Slides

A note may be gradually altered over time until it reaches a new pitch. This is achieved with the - operator.

slide: h e2 - e c3;

e f3, slide,
h b3, slide

To chain slides, use the z duration for the destination note:

h e2 - z c3, h c3 - z f4, e f4 - z d3

This ensures that the entire duration of the slide is dictated by the duration of the source note.

Advanced features

Effects

Dynamics like gain, reverb, detuning, instrument, and distortion can be easily altered in a composition using the '@' tag.

@reverb 2/1.1/0.7,
@gain 75,
@instrument square,
h g3, w a5,

@instrument sine,
h g3, w a4

In the above example, the instrument is set to square and later changed to sine. Reverb and gain are set for the entire piece.

Reverb

@reverb accepts 3 optional parameters delimited with '/': channel #, reverb length as a function of the sample rate, and decay rate.

Gain

@gain accepts 1 parameter: the amount of gain from 0 (mute) to 100 (maximum volume).

Detune

@detune accepts 1 parameter: the value in cents to detune a frequency.

Instrument

@instrument accepts 1 parameter: the instrument name.