Vinyl records use grooves on the disc to encode the music. But not the Evil Eye optical synth by Belgian collective Indianen:
Joshua Kopstein of The Verge has the story and video clip: Link
Instead of cutting grooves onto a surface, custom software allows the artists to design and print black-and-white waveform patterns as PDFs, which are then screenprinted onto 12-inch optical discs and played back on a turntable using specialized light-sensing hardware instead of a needle. The waveforms can be either shaped manually in the software or imported / modified from existing patterns.
The "eye" hardware's designer, Tim Knapen, says he opted not to use a smartphone camera as the sensor, because it would have unnecessarily complicated the process. "We use a simple light-to-voltage converter that doesn't do any processing. An iPhone app would require some visual processing but more importantly also some kind of synthesizer. In the setup we used, all the sound is encoded in the disks and there is no need for anything digital."