Bingo. We certainly learned about Cooley-Tukey in undergrad back then. That power station was 100% Hitachi Heavy Industries turnkey. The control rooms had Hitachi mainframe and some minicomputers running proprietary real time OS (I guess). These were the days when the video controller for a colour industrial process control raster display CRT was a waist-high cabinet. So you'd transduce the flicker and then transmit it via analogue current loop to a rack in the control room annex, convert back to voltage, A/D it... and crunch the FFT on one of the control room computers. Something like that. Cheap distributed compute just wasn't a thing at the time.

this is so cool, thanks for sharing :)