Answer: Commuters

Spin the dial on a radio and when you land on NPR, you’ll know it. It’s not the musical interludes between radio shows that tips you off (although the presence of a sudden burst of jazz after the news is a pretty strong give away), but the very distinct sound that National Public Radio shows have. It’s a crisp, bright, and clear sound that’s unmistakable.

While you can attribute part of the effect to the use of very high quality audio equipment (they use top-of-the-line Neumann U87 microphones) and a very low-reverberant studio, the big part of it is that the audio is tuned for very specific listeners: automotive commuters. Because the vast majority of NPR listeners are listening in their cars, NPR’s audio engineers have tuned the audio to drop frequencies below 250 hertz, which makes the audio extra crisp and clear for people in cars (where the ambient noise from the car, road, and surrounding traffic is in the low frequency range).