No, that's not a piece of pixel art, nor is it a Myst puzzle key. It's a lovely spatial sound synthesizer flash program that lets you plug in notes like a monochromatic Lite-Brite toy that creates music depending on which axis information you feed it. It's simple enough to make it easily accessible by anyone, and detailed enough with its noises to make it crazily addictive.
Thanks to @JayHitcher on Twitter for sharing his musical creations with me last night. Feel free to share your grid sheet music pics in the comments below! The picture above is decent, but this is the one I created last night that I was the most proud of. You can play Sembeo here, or if you desire even more musical options, there's a Sembeo double matrix here! Just click some turn some blocks on or off and the program will do the rest!