node.js speaker sine wave playing example

node-speaker-example

var Speaker = require('speaker');
var Readable = require('stream').Readable;
// node v0.8.x compat
if (!Readable) Readable = require('readable-stream/readable');

// Examples : 
//  makeSound(440,0.5).play(8);   // frequency, duration, delay

let s440 = makeSound(440, 1.0);
s440.play(); // play immediately
s440.play(2); // play 2 seconds later

// makeSound().play();  // cannot play simultaneously with s440.play() above

function makeSound(f, d) {
	// the frequency to play
	let freq = f || 440.0; // Concert A, default tone

	// seconds worth of audio data to generate before emitting "end"
	let duration = d || 0.4;

	return {
		play: play
	};

	function play(delay) { // delay in seconds
		let d = delay || 0;
		setTimeout(() =>
			playIt(), delay * 1000);
	}

	function playIt() {
		// A SineWaveGenerator readable stream
		let sine = new Readable();
		sine.bitDepth = 16;
		sine.channels = 2;
		sine.sampleRate = 44100;
		sine.samplesGenerated = 0;
		sine._read = read;
		sine.pipe(new Speaker());
	}

	// the Readable "_read()" callback function
	function read(n) {
		let sampleSize = this.bitDepth / 8;
		let blockAlign = sampleSize * this.channels;
		let numSamples = n / blockAlign | 0;
		let buf = new Buffer(numSamples * blockAlign);
		let amplitude = 32760; // Max amplitude for 16-bit audio

		// the "angle" used in the function, adjusted for the number of
		// channels and sample rate. This value is like the period of the wave.
		let t = (Math.PI * 2 * freq) / this.sampleRate;

		for (let i = 0; i < numSamples; i++) {
			// fill with a simple sine wave at max amplitude
			for (let channel = 0; channel < this.channels; channel++) {
				let s = this.samplesGenerated + i;
				let val = Math.round(amplitude * Math.sin(t * s)); // sine wave
				let offset = (i * sampleSize * this.channels) + (channel * sampleSize);
				buf['writeInt' + this.bitDepth + 'LE'](val, offset);
			}
		}

		this.push(buf);

		this.samplesGenerated += numSamples;
		if (this.samplesGenerated >= this.sampleRate * duration) {
			// after generating "duration" second of audio, emit "end"
			this.push(null);
		}
	}
}