"Adventures in time and space," the announcer intones. "Told in future tense!" There is a gong, a pause, and then: "Dimension X!" followed by an echo, "X! X! X!"
It's a cheesy introduction, but forgivable -- it was recorded in 1950. "Dimension X" was a radio program that broadcast science fiction stories in 1950-51. Those were the last days of the golden age of radio, but the early days of the golden age of science fiction. The overlap is a fortunate coincidence.
The show broadcast stories by science fiction stars, including Isaac Asimov and Robert Heinlein.
The website Open Culture highlights four of the shows. In addition to Vonnegut's story, there is "There Will Come Soft Rains" by Bradbury, "Pebble in the Sky" by Asimov and "The Green Hills of Earth" by Heinlein.
The stories were adapted for radio, so there are actors performing the dialogue. And, of course, there are plenty of sound effects, including: spooky music, whistling spaceship sounds and an angry milling crowd.
In Bradbury's story, two women are speaking on "the televiser" -- one tells her daughter to come see her aunt and say hello -- an echo of the visual world that even then was marginalizing the radio story being performed.