61 lines
1.9 KiB
JavaScript
61 lines
1.9 KiB
JavaScript
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'use strict'
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/**
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* Code adapted from:
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* http://blogs.msdn.com/b/dawate/archive/2009/06/24/intro-to-audio-programming-part-3-synthesizing-simple-wave-audio-using-c.aspx
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*/
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const Readable = require('stream').Readable
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const bufferAlloc = require('buffer-alloc')
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const Speaker = require('../')
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// the frequency to play
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const freq = parseFloat(process.argv[2], 10) || 440.0 // Concert A, default tone
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// seconds worth of audio data to generate before emitting "end"
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const duration = parseFloat(process.argv[3], 10) || 2.0
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console.log('generating a %dhz sine wave for %d seconds', freq, duration)
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// A SineWaveGenerator readable stream
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const sine = new Readable()
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sine.bitDepth = 16
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sine.channels = 2
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sine.sampleRate = 44100
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sine.samplesGenerated = 0
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sine._read = read
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// create a SineWaveGenerator instance and pipe it to the speaker
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sine.pipe(new Speaker())
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// the Readable "_read()" callback function
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function read (n) {
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const sampleSize = this.bitDepth / 8
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const blockAlign = sampleSize * this.channels
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const numSamples = n / blockAlign | 0
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const buf = bufferAlloc(numSamples * blockAlign)
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const amplitude = 32760 // Max amplitude for 16-bit audio
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// the "angle" used in the function, adjusted for the number of
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// channels and sample rate. This value is like the period of the wave.
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const t = (Math.PI * 2 * freq) / this.sampleRate
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for (let i = 0; i < numSamples; i++) {
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// fill with a simple sine wave at max amplitude
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for (let channel = 0; channel < this.channels; channel++) {
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const s = this.samplesGenerated + i
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const val = Math.round(amplitude * Math.sin(t * s)) // sine wave
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const offset = (i * sampleSize * this.channels) + (channel * sampleSize)
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buf[`writeInt${this.bitDepth}LE`](val, offset)
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}
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}
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this.push(buf)
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this.samplesGenerated += numSamples
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if (this.samplesGenerated >= this.sampleRate * duration) {
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// after generating "duration" second of audio, emit "end"
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this.push(null)
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}
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}
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