goertzel

Implements the Goertzel algorithm for efficient frequency detection.

example

var goertzel = require('goertzel')
 
var opts = {
  // 1 kHz
  targetFrequency: 1000,
  // samples per second
  sampleRate: 10000,
  // samples per frame
  samplesPerFrame: 100
}
 
var detect = goertzel(opts)
 
// generate sine wave at some Hz and time (ms)
function sin (hz, t) {
  return Math.sin(Math.PI * 2 * t * hz)
}
 
// sine at 1 kHz for 100 samples
var data = []
for (var i = 0; i < opts.samplesPerFrame; i++) {
  var v = sin(opts.targetFrequency, i / opts.sampleRate)
  data.push(v)
}
 
console.log(detect(data))

true

methods

var detect = goertzel(opts={})

Returns a function set to detect a single frequency.

opts is mandatory, and has some required and optional parameters:

• opts.targetFrequency (required) - the frequency, in Hertz, to detect the presence of
• opts.sampleRate (required) - how many samples are taken per second. For best results, this should be at least twice the Nyquist frequency. 2.5x works well.
• opts.samplesPerFrame (required) - how many samples will be included in each frame to be tested.
• opts.threshold (optional) - The Goertzel algorithm returns a relative magnitude of how well the samples match the targetFrequency. Set this to control the threshold. In general, the default value can be used safely.

detect(data)

Returns a boolean: true if the targetFrequency is present in the samples, and false otherwise.

data is expected to be compatible with a Float32Array.

install

With npm installed, run

$ npm install goertzel

license

MIT