How do the scientists measure the pitch?

Voice One: This is what scientists say the sun sounds like the equivalent of a solar heartbeat. Solar scientists used listening devices to unravel some of the mysteries of Earth’s nearest star. It’s not the actual sound. Sound can’t travel through the vacuum of space. But [this is] a recreation based on the waves recorded by the devices.
    Each pitch corresponds with the movement and vibrations of various hot gasses as they flow like rivers beneath the sun’s surface-- similar to how trade winds blow on Earth.
    Scientists translate the sounds they make into images. This allows a unique glimpse inside the sun’s complex architecture, to answer questions about its temperature, chemical makeup, and how gasses inside ebb and flow.
    Voice Two: What we’re finding is that there are very interesting structures inside. There’s an equatorial belt of faster moving material. And then, farther up near the poles, we believe that them’s a jet stream of material moving about 60 miles an hour up at a very north latitude.