2-op FM synthesis, beginning with low-frequency oscillation

fm.waapi.js

/* ****** low-frequency modulation (vibrato) ******
This example shows how to use a second oscillator to 
modulate the frequency of a oscillator over time. */

ctx = new AudioContext()

// create our primary oscillator, called the "carrier"
// in frequency modulation terminology (from radio)
carrier = ctx.createOscillator()
carrier.type = 'square'

// create an oscillator for modulation
mod = ctx.createOscillator()
mod.type = 'sine'

// slow oscillation... 
mod.frequency.value = .5

// by default, oscillators output values in the range of {-1,1}.
// To create a wider range we use a gainNode
gainNode = ctx.createGain()

// scale input by 20... {-1,1} becomes {-20,20}
gainNode.gain.value = 20 

// route modulating oscillator into gain node
mod.connect( gainNode )

// plug the gain node into the frequency of
// our carrier
gainNode.connect( carrier.frequency )

// connect carrier to master output
carrier.connect( ctx.destination )

// start both oscillators
mod.start( ctx.currentTime )
carrier.start( ctx.currentTime )


/************* classic 2-op FM Synthesis *****************/
ctx = new AudioContext()

// gong
// const index = .95
// const cmRatio = 1.4
// const attack .01
// const decay = 5

// bass
// const index = 1
// const cmRatio = 3
// const attack = .001
// const decay = .25

// glockenspiel
const index = 1
const cmRatio = 3.5307
const attack = .01
const decay = .5

playNote = function( frequency, duration ) {
	// create our primary oscillator
	let osc = ctx.createOscillator()
	osc.type = 'sine'
  osc.frequency.value = frequency

	// create an oscillator for modulation
	let mod = ctx.createOscillator()
	mod.type = 'sine'

	// change oscillation speed...
	mod.frequency.value = frequency * cmRatio

	// this will amplify our modulator
	// and control the range of modulation
	let modGainNode = ctx.createGain()
	modGainNode.gain.value = frequency * index

	mod.connect( modGainNode )

	// plug the gain node into the frequency of
	// our oscillator
	modGainNode.connect( osc.frequency )

	let envelope = ctx.createGain()
  envelope.gain.linearRampToValueAtTime( 1, ctx.currentTime + attack )
  envelope.gain.linearRampToValueAtTime( 0, ctx.currentTime + attack + decay )
	
	osc.connect( envelope )
	
	envelope.connect( ctx.destination )
	mod.start( ctx.currentTime )
	osc.start( ctx.currentTime )

  // remove the node two seconds from
  // the current audio time
  osc.stop( ctx.currentTime + duration )
}

// 220 Hz, 2 seconds
playNote( 880, 2 )