Confused by Ozpeter's last post. Why not playback a known recording on known monitors, record the sound with a particular set of mics before the mod and the same mics after the mod? That would seem a better before and after than no before and after?
That method (which of course I've used recently) is fine for giving an indication of obvious differences between devices (such as built in mics which can be expected to sound quite different on inexpensive recorders), but if I heard a difference between modded and unmodded recorders on such a test, my first suspicion would be that the test was faulty rather than that there was a significant difference between the recorders. For instance, the setup would have to be very carefully replicated in all respects, including very precise placement of the mics in the room.
Actually a better test - at least one that I'd be more impressed by, fwiw - would be to feed a line input at reduced level into the mic inputs before and after (Mackie mixers for instance used to provide an optional mic level output). Under those conditions, the recording should sound pretty much identical to the original test file (if the test was done correctly) and it might even be possible to obtain some indication of the unmodded and modded difference by inverting the before and after recordings against the test file. Of course you wouldn't expect a null inversion, but you might - perhaps - get something which would reinforce what your ears were telling you (bearing in mind that your ears might be convincing you that the mod was better even if it wasn't).
When I think of all the posts on all the forums were mods to recorders are discussed, it makes me deeply suspicious that as far as I have seen, nobody has really tried any such test to prove the differences - and also to eliminate the possibility that (for instance) a modded recorder which appeared to offer an
improved HF response wasn't actually simply providing an
exaggerated HF response. It's essential to be sure that the result of a mod is a more accurate recording, rather than just a more sexy sounding recording which could equally have been created in post production with a bit of eq or whatever.
You can probably detect that this subject is one of my many obsessions...