I always thought it was called a “white-noise generator”...simple electronic device. Or a “pink-noise generator”.
The latter used to EQ a sound system to a room and eliminate “ringing” (resonant frequencies).
Sounds like the roaring/air rushing of a jet engine up close...It’s the equal dB of all audible frequencies.
In a huge venue, applied artfully, it would just sound like the echo of applause and audience noise.