Here is a small description of what it is:
And this is the kind of output it can give, comparing a Sega Genesis Model 1 VA3 vs a Sega Nomad:MDFourier is an open source software solution created to compare audio signatures and generate a series of graphs that show how they differ. The software consists of two separate programs, one that produces the signal for recording from the console and the other that analyses and displays the audio comparisons.
The information gathered from the comparison results can be used in a variety of ways: to identify how audio signatures vary between systems, to detect if the audio signals are modified by audio equipment, to find if modifications resulted in audible changes, to help tune emulators, FPGA implementations or mods, etc.
And this is a VA3 with Sega CD compared to a Model 2 VA1.8 with Sega CD:
Please check out http://junkerhq.net/MDFourier for the full documentation, interpretation informatiom and downloads.