This is a digitally synthesized version of the sound produced by current choppers on board the "jeumont element 041/042 train" used in the montreal metro. It is a five-note sequence of tones (90 hz, 120 hz, 180 hz, 240 hz, 360 hz) produced as the train accelerates out of the station. I could not make a recording of the actual jeumont train as the train was scrapped in 2018, which was before i even made my account!.
Author: Chungusa