Genesis dual-mode questions

When comparing the sound of a Genesis dual-mode passenger locomotives to a GE freight locomotive, I've noticed that the Genesis engine sounds as if it's revving at a higher speed even during station stops. Do these engines rev at a constant speed? Is this related to the HEP unit?

Jim D.

Not really Dave without the HEP the engine goes down to regular Idle. But with HEP it runs from 770 to 1050 depending on Demand.
An AC locomotive does not notch up same as a DC unit however it lets load go up and the engine tries to keep up or anticipate the load.