Audio Check:

This page helps you evaluate headphones or earbuds online, and determine which one offers the best performance when comparing different pairs. Audiocheck is a sound testing site created by sound designer Dr. Ir. Stéphane Pigeon. The site contains various “test” files for audio benchmarking, a tone generator you can use to create .wav files, and a testing section to see how well-trained your ear is (or isn’t). The tracks aren’t music—they’re noises or sounds meant to measure the performance of your equipment.

I’m nowhere near enough of an audiophile to need this site but I know some of you are.