It’s not exactly synesthesia, but it’s interesting nonetheless.

While we’ve all seen plenty of waveforms (a visualization of sound first captured in 1860), not everyone has seen actual sound waves.

NPR has shared a video that shows off a photography technique called Schlieren Flow Visualization, invented by German physicist August Toepler in the mid-19th century. As explained in the video, the set-up requires a pair of parabolic mirrors (among other things) to capture light as it bends through air.

Michael Hargather, a professor of mechanical engineering at New Mexico Tech, uses SFV and high-speed cameras to capture the shock waves caused by explosives. Watch sound waves — which travel at 761.2 miles per hour — below.