Measuring speed with acoustics and a tape recorder...
That looks very clean, I haven't managed to get graphs that sharp. On the up side, I don't see so many harmonics on mine, just a single line that at a frequency identical to engine RPM.
Philly, how do you keep the graphs clean at the point of flyby. Do you normalize the volume? When I play a tape into the spectrograph, I get a big blob on the graph at flyby because it's so loud.
Jason