FS2004 Engine pitch when approaching in tower view

What controls the spike in engine pitch as the plane approaches? There must be a control for the rate of the pitch, and the distance at which it kicks in. I would love to know what to adjust so the sound of the simulated Doppler effect during a flypast in the tower POV, doesn't start as high as a sewing machine at full boar. Does anyone know what and where the control cfg is for this audio effect?