A clustered nods.js module to create spectrograms from pcm audio data

Install

Spectro can be installed via npm:

npm install spectro

Usage

By using a cluster of workers to process the computational expensive stuff the execution time can be decreased dramatically. The spectrogram class is a writable stream where the data can be piped into. So the easiest way to use it is to pipe a wav file into it:

const Spectro = require('spectro')
const fs = require('fs')

var sp = new Spectro()
var audioFile = fs.createReadStream('file.wav', {start: 44}) // Note: The first 44 bytes are the wav-header

// The file stream can simply be piped into the Spectro instance
audioFile.pipe(sp)

// Check when the file stream completed
var fileRead = false
audioFile.on('end', () => fileRead = true)

// The data event can be used to work with recently processed data from the workers
spectro.on('data', (err, frame) => {
    if (err) console.error('Spectro data event has an error', err)
    // frame contains an index of the processed frame and a data section with the processed data
})

spectro.on('end', (err, data) => {
    if (err) return console.error('Spectro ended with an error', err)
    // The 'end' event always fires when spectro has reached the end of the currently processable data
    // Therefore we should check if the file was read completely before using the data
    if (fileRead !== true) return

    // Stop spectro from waiting for data and stop all of it's workers
    spectro.stop()

	// The spectrogram can e.g. be drawn with third party modules such as pngjs
	// Examples therefor can be found in examples/...
})

Methods

Constructor

The constructor can be called with an options object with these options:

Option | Default | Description -----------|---------------|------------ bps | 16 | Bits per second of the audio channels | 1 | The channels count of the audio (allowed: 1) wSize | 1024 | The window size being used for the dct wFunc | 'Hamming' | The window function to use overlap | 0 | The overlap size: 0 <= overlap < 1 workers | <CPU cores> | How many workers should be created to process the data

Instance methods

• stop() - Stops all workers from further processing of incoming data
• start() - Recreates the workers that compute the spectrogram on incoming data
  Note: start() will automatically be called with the constructor
• clear() - Triggers stop() and resets all data and the time measuring
• executionTime(): number - Returns the execution time in ms

Static methods

• colorize(colorMap): Function - Returns colorization function for the amplitudes.
• maxApplitude(): number - Returns the maximum applitude of a spectrogram
• minApplitude(): number - Returns the minimum applitude of a spectrogram

Events

Event | Parameters | Description -------|----------------|------------ data | err, frame | When a new frame was processed. frame has an index and a data array end | err, data | When all possible windows where processed. This event can be called several times before the complete audio has been piped into the Spectro instance. data is a two-dimensional array with the amplitudes

Window functions

The following window functions are implemented:

• Square
• Hamming
• VonHann (Hanning)
• Blackman (default)
• BlackmanHarris
• BlackmanNuttall
• Bartlett

Limitations

Only mono is supported at the moment.