The p5.js (http://p5js.org/) library for creative coding on the web includes sound support:

http://p5js.org/reference/#/libraries/p5.sound

Do you want to create a cool visualization of your favorite song? If you do, claim this task!

Some useful references from the p5.js reference:

http://p5js.org/reference/#/p5.Amplitude

http://p5js.org/reference/#/p5.FFT

An neat starting p5.js guide from another Google Code-in student:

http://codein.namanyayg.com/p5/