Interactive tool showing how sound waves work

Josh Comeau, a software developer at the Khan Academy, has created a superb interactive tutorial showing how sound-waves work.

It's really, really good. I've used synthesizers for years, but never fully understood the soundwave mechanics behind "subtractive" and "addictive" synthesis -- and while I generally understood the idea of noise-cancelling headphones, I couldn't entirely visualize the physics of what was going on.

This tutorial walks you through the grit of how the sound waves are interacting with each other in each case, presenting you with interactive gewgaws to tweak so that you build up a sensual, intuitive appreciation for what's going on. It's really worth 10 minutes of your time -- check it out!