fft-windowing/README.md

Applies a windowing function to an array of data, making it ready to be FFT'd.

**nodejs-fft-windowing** is a [node.js](http://nodejs.org/) module that applies a [windowing function](http://en.wikipedia.org/wiki/Window_function) to an array of data, making it ready to be [FFT](http://en.wikipedia.org/wiki/Fast_Fourier_transform)'d.

[This article](http://www.ni.com/white-paper/4844/en) by [National Instruments](http://uk.ni.com/) gives a good introduction to why windowing functions are useful.

## Installation ##

If you have [npm](https://npmjs.org/) installed, just run:

```
npm install fft-windowing
```

## Usage ##

The [Hann (Hanning) window](http://en.wikipedia.org/wiki/Window_function#Hann_.28Hanning.29_window) is a good general-purpose window. You would use it like so:

```javascript
var windowing = require('fft-windowing');

var raw = [2, 2, 0, -2, -2, 0, 2, 2];

var windowed = windowing.hann(raw);

```

The resulting `windowed` variable is then ready to be fed through a Fast Fourier Transform. A good [node.js](http://nodejs.org/) module to use would be [this](https://npmjs.org/package/fft) one.

The following windows are available:

- [hann](http://en.wikipedia.org/wiki/Window_function#Hann_.28Hanning.29_window)
- [hamming](http://en.wikipedia.org/wiki/Window_function#Hamming_window)
- [cosine](http://en.wikipedia.org/wiki/Window_function#Cosine_window)
- [lanczos](http://en.wikipedia.org/wiki/Window_function#Lanczos_window)
- [gaussian](http://en.wikipedia.org/wiki/Window_function#Gaussian_windows)
- [tukey](http://en.wikipedia.org/wiki/Window_function#Tukey_window)
- [blackman](http://en.wikipedia.org/wiki/Window_function#Blackman_windows)
- [exact_blackman](http://en.wikipedia.org/wiki/Window_function#Blackman_windows)
- [kaiser](http://en.wikipedia.org/wiki/Window_function#Kaiser_windows)
- [nuttall](http://en.wikipedia.org/wiki/Window_function#Nuttall_window.2C_continuous_first_derivative)
- [blackman_harris](http://en.wikipedia.org/wiki/Window_function#Blackman.E2.80.93Harris_window)
- [blackman_nuttall](http://en.wikipedia.org/wiki/Window_function#Blackman.E2.80.93Nuttall_window)
- [flat_top](http://en.wikipedia.org/wiki/Window_function#Flat_top_window)

The following windows can also accept an extra parameter, `alpha`:

- [gaussian](http://en.wikipedia.org/wiki/Window_function#Gaussian_windows) defaults to 0.4
- [tukey](http://en.wikipedia.org/wiki/Window_function#Tukey_window) defaults to 0.5
- [blackman](http://en.wikipedia.org/wiki/Window_function#Blackman_windows) defaults to 0.16
- [kaiser](http://en.wikipedia.org/wiki/Window_function#Kaiser_windows) defaults 0.3

You would use it like this:

```javascript
var windowing = require('fft-windowing');

var raw = [2, 2, 0, -2, -2, 0, 2, 2];

var windowed = windowing.kaiser(raw, 0.5);

```

## Tests ##

Run `node tests/fft-windowing-tests.js`. This should generate a file called `fft-windowing.pdf` in the root directory which shows what happens if you apply each windowing function to a uniform array.

## LICENSE ##

MIT