javascript-dsp-examples

Examples of digital signal processing in pure JavaScript. The code is adapted from node-fft (fft-js) and remains intended primarily for example purposes as it is not optimised for efficiency.

Examples

Examples are provided in the /bin folder, each of which can be run with the command npm run exampleName. Clone this repository and run the commands from its root folder.

velocityOverall

Determine the velocity overall from a time series of acceleration samples.

npm run velocityoverall

The velocity overall is calculated as follows:

• Remove any DC offset from the samples
• Split into (up to 4) non-overlapping time series of at least 256 samples
• Application of Hann window to each time series using hannWindow(samples)
• Conversion to frequency domain using fft(samples, samplingRate)
• Integration over each frequency bin to obtain velocities
• RMS of velocities using rms(values) divided by square root of Hann noise bandwidth
• Average of the (up to 4) overall velocities

Assuming acceleration samples are in m/s2 and the samplingRate is in Hz, the velocity overall will be in m/s. Edit the parameters in bin/velocityoverall to test different scenarios.

dsp.js

The lib/dsp.js file provides a JavaScript implementation of a Fast Fourier Transform (FFT), Hann window, and root mean square calculation.

fft(samples, samplingRate)

Compute the Fast Fourier Transform of the given Array of samples captured at the given samplingRate (typically in Hz). For example, the original test case would be implemented as follows:

const dsp = require('./lib/dsp.js'); // Edit path as required

let samples = [ 1, 1, 1, 1, 0, 0, 0, 0 ];
let samplingRate = 44100;

console.log(dsp.fft(samples, samplingRate));
// {
//   magnitudes: [ 4, 2.613125929752753, 0, 1.0823922002923938 ],
//   frequencies: [ 0, 5512.5, 11025, 16537.5 ],
//   numberOfBins: 4
// }

hannWindow(samples)

Compute the Hann window of the given samples, returning the windowed samples as a new Array.

const dsp = require('./lib/dsp.js'); // Edit path as required

let values = [ 1, -1, 1, -1, 1 ];

console.log(dsp.hannWindow(values));
// [ 0, -0.4999999999999999, 1, -0.5000000000000001, 0 ]

rms(values)

Compute the root mean square of the given Array of values, for example:

const dsp = require('./lib/dsp.js'); // Edit path as required

let values = [ 0, 1, 1, 2, 3, 5, 8, 13, 21, 34 ];

console.log('The calculated RMS is', dsp.rms(values));
// The calculated RMS is 13.674794331177344

dcOffset(values, offset)

Offset the given values by the given offset. If no offset is provided, the mean of the values will be used as the offset, effectively removing any DC offset from the values.

The values can be either an Array of Numbers of an Array of Array. In the latter case, the function will use self-recursion.

const dsp = require('./lib/dsp.js'); // Edit path as required

let values = [ 1, -1, 1, -1, 1 ];

console.log(dsp.dcOffset(values, 1));
// [ 2, 0, 2, 0, 2 ]

values = [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ] ];

console.log(dsp.dcOffset(values));
// [ [ -0.5, 0.5 ], [ -0.5, 0.5 ], [ -0.5, 0.5 ] ]

createPowerOfTwoLengthSubSamples(samples, minLength, maxNumberOfSubs)

Split the given samples into a set of subsamples, up to the given maximum number of subsamples, each of the given minimum length or a larger power of two, whichever is greater, for example:

const dsp = require('./lib/dsp.js'); // Edit path as required

let samples = [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ];

console.log(dsp.createPowerOfTwoLengthSubSamples(samples, 2, 2));
// [ [ 0, 1, 2, 3 ], [ 6, 7, 8, 9 ] ]

console.log(dsp.createPowerOfTwoLengthSubSamples(samples, 2, 4));
// [ [ 0, 1 ], [ 3, 4 ], [ 6, 7 ], [ 9, 10 ] ]

Contributing

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License

MIT License

Copyright (c) 2025 reelyActive

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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