Time stretching is the process of changing the speed or duration of an audio signal without affecting its pitch. Pitch scaling or pitch shifting is the opposite: the process of changing the pitch without affecting the speed. Similar methods can change speed, pitch, or both at once, in a time-varying way.
Kali uses a WSOLA-like algorithm to do high-quality time stretching in the browser
Try a demo here.
Get Kali from the releases page.
Kali will be published to npm soon.
Create a new instance
var kali = new Kali(numChannels);
Set parameters for time stretching. Setting
useQuickSearch to true will speed up processing at the expense of some quality. By default, it is set to false. The difference is not noticeable in many cases so try setting it to true if you need more performance.
kali.setup(sampleRate, stretchFactor, useQuickSearch);
Feed Kali some data and tell it to process.
dataToInput should be a Float32Array of interlaced samples.
Read data out into a target array.
targetArray should be a Float32Array.
var samplesRead = kali.output(targetArray);
Once you're done feeding data, tell Kali to flush its buffers and continue reading data.
That's it! See
Test.ts in the examples folder for a complete example of usage.
If you want to change tempo during stretching, you can call
setTempo (with a new stretch factor) while feeding data. This will let you smoothly change between tempos. See
Test.ts for an example.
For complete documentation, see https://kali.readme.io/docs
By using TypedArrays and views on TypedArrays, Kali operates very efficiently. That said, this is an early release and performance hasn't been optimized as much as possible. Pull requests are welcome!
- Clone or download this repository
- Put an mp3 file named
- Start a server in that directory
python -m SimpleHTTPServer
- Open your browser and navigate to the test page
The developer console will show the progress of the file being stretched. Once the stretch is complete, the slowed-down version will begin playing. This example slows down a song by 4% (so a 125 bpm song will be slowed down to 120 bpm).
To change this (or anything else about the example), edit
Test.ts in the
examples directory and build as shown below.
npm install // build examples webpack --config webpack.config.test.js // build Kali webpack // build minified Kali webpack -p
Kali is based on ideas and code from SoundTouch and libsox, both of which are LGPL. Therefore, Kali is also LGPL