Let me clarify about later model lowpass filtering.
Model 2 of the Genesis/MageDrive actually uses second-order (12db/oct) lowpass filtering which is steeper that Model 1 first-order lowpass (6db/oct).
Sega used a steeper second-order filtering on Model2 because it had terrible audio quality.
The Lowpass emulated in GenPlusGX is first-order ONLY thus can never sound like the later Model2 filtering.
The 0.4//0.6 values we talk about correspond to a frequency the first-order lowpass starts at, but could never sound like second-order lowpass simply because the code in GenPlusGX is for first-order ONLY.
Changing the 0.x value would be like changing the capacitor which determines the cut-off frequency on the real Model1 console, and will NOT get you closer to the Model2 sound in any way, not that you want too anyway.
According to my measurement of various Model1 consoles, there is virtually no difference in cut-off frequency, therefor a single correct default value in GenPlusGX will do to match that.
Therefor, we should use the correct measured value for Model1 and not try to guess or remember how your sounded or should sound, I urge you to understand that.
Eventually the end user can do whatever he wants, but please don’t make the wrong/guessed value as default.
The 60% value be ekeeke comes from what he though sounded the same from his Wii running GenPlusGX.
He didn’t actually measure the frequency response, but tuned to what sounded close to him and not even in direct comparison.
I’m still waiting for a response from wertz about what method he used to get the 0.6 value, which he CONFIRMS to be correct.