Update index.js

- Use Float32Array instead of an untyped JS array for audio buffers
- Fix a typo in the implementation of Paul Kellet's algorithm
- Optimize away branching and unnecessary repetitive math inside the normalization loop

I adapted this code for use in [one of my small personal projects](http://xsznix.github.io/binaural/) and would like to contribute some of my changes back. The adapted code can be found in [this file](http://xsznix.github.io/js/noise.js).

Have a nice day!