Gradients are all around us in the form of airflow. As we move about at different speeds, refractive variations caused by density gradients distort our sense of light and sound. Higher velocity means more distortion, or at least a more visualized shift among images that remain in focus.
(Refraction is also why many of us have trouble seeing as we get older. Next time you stub your toe squinting to locate your eyeglasses, blame the gradients. Shaking your fist in the air at fandom fluid densities is entirely optional).
In 1864, German physicist Augst Toepler invented Schlieren photography as a way to visualize airflow current. Putting it simply, rays of light change when patches of air at varying densities are forced to pass through each other. Placing a concave mirror with a long focal distance helps to illuminate these shifts, which can be photographed using a knife edge or razor blade in front of a camera lens.
For this strange piece, Suss Müsik attempted to recreate a Z-type Schlieren setup with a guitar, two looping pedals, and a pitch-shifting delay pad. The original concept was to cut off one set of loops (the “lamp”) while “refracting” another set of loops (the “mirror”) with various sawtooth/reverb effects. The results didn’t quite hit that mark, but there remains some auditory evidence of densities splitting in motion and later converging.
The piece is titled Schlieren and was recorded live to 8-track. The image is a Schlieren photograph of shock waves produced by an in-flight T-38 Talon, the world’s first supersonic jet trainer.
Image credit = NASA & US Air Force: J.T. Heineck / Ed Schairer / Maj. Jonathan Orso / Maj. Jeremy Vanderhal, Public domain, via Wikimedia Commons