Audio memory is about 10 seconds so you need to play both files at the same time and switch between them to hear the difference.
I doubt the Spectrum view in Audacity will be of much use with subtle differences like a slightly more metallic sound. It would have to be very obvious to see that in such a graph.
It could also be a slightly different EQ setting between versions of fasttracker. Is there an EQ in there? If not, maybe it's hard coded and can be looked up in the source?
You could check that my way too, which involves a white noise and a 32 band spectrum analizer with hold function.
