A web based client side cross-correlation (using WebAudio).
It is a cross-correlation implementation built entirely for client-side web applications. The project is written in TypeScript but uses WebPack (as well as unminified-webpack-plugin) and ts-loader to output a JavaScript callable interface.
There are two underlying cross-correlation implementations when calling xcorr.ts:
A purely WebAudio implementation of the cross-correlation algorithm, using offlineAudioContexts to improve speed asynchronously.
An implementation of the Generalized Cross-Correlation with Phase Transform which uses a WebAssembly port (PulseFFT) of kissfft to run on a client browser.
Depending on the method of cross-correlation, certain extra dependencies will need to be added. To run xcorr.ts in WA_XCORR mode only WebAudio features will be needed. This can be simply setup by including the built version of the code libxcorr.js in the entry HTML.
<script src="js/libxcorr.js" type="text/javascript"></script>
On including this, an xcorr object will be appended to the window as a singleton that can be used. By default the mode will be set to WA_XCORR, but can be set explicitly:
xcorr.setMode('waxcorr'); // or 'gccphat'The cross-correlation process can then be called asynchronously on two Float32Array buffers:
// buffer0: Float32Array
// buffer1: Float32Array
// correlatedBuffer: Float32Array
const correlatedBuffer = await xcorr.correlate(buffer0, buffer1);Or if required, a time-lag estimate can be called directly and the correlated buffer can be ignored:
// buffer0: Float32Array
// buffer1: Float32Array
// timeLag: number
const timeLag = await xcorr.timeLag(buffer0, buffer1);This will output the best found peak of time lag from the cross-correlation and uses Lagrangian interpolation with bias correction for fractional delays.
As the GCC-PHAT approach requires frequency domain transformation and manipulation, extra dependencies are required in.
Currently PulseFFT is setup asynchronously and requires a function being appended to the window so that xcorr.ts can load it correctly. Firstly the index.js script supplied with PulseFFT must be modified slightly to have the following appended:
// pulse/index.js
window.initPulse = loadPulse;This file can then be included in the script tag and will search for the PulseFFT compiled WASM (make sure it is within the top level directory under a folder called pulse);
<script src="/pulse/index.js"></script>
Please follow setup instructions at PulseFFT for more information.
Mathjs is used for extra complex data type manipulation within xcorr.ts and is needed in the window scope. This can be simply added by downloading the LTS version and including in the script tag as follows:
<script src="math.js" type="text/javascript"></script>
Magnus Woodgate