It was early in the morning, but Mark Fahey had been awake for hours. A biomedical engineer turned North Korean propaganda expert, he had spent most of the night tinkering with a radio in his room at the Yanggakdo International Hotel, secretly recording the opening moments of Pyongyang FM Pangsong.

While he listened to the station’s typical offering of classical music and propaganda, another microphone and recorder were set up next to an open window to capture the sounds of the city as it roused itself awake. It was August 2011, and the sun hung low on the horizon. Fahey expected to pick up the sound of the dredging work taking place along the Taedong River.