Implement such LPF and i will add it
Some Genesis songs were making my ears bleed. I'm looking at you, Thunder Force II,III,IV
So I took a shot at implementing the appropriate filters. I tried to find a working, open, IIR filter and couldn't get one that worked. So I just wrote one.
I made IIR 1st and 2nd order filters and then wrapped them in two Genesis specific modules.
Genesis Model 1 has a 1st order filter somewhere in 2.8-3.7khz and covers all audio.
Genesis Model 2 has a filter similar to model 1 but higher in frequency. And they also have a separate 2nd order filter around ~6.8khz that is for the FM audio only.
JamesF was nice enough to send me audio samples from his original systems and mister and I was able to match the response of the filters very well. I'm attaching plots showing the target response of the filter along with the computed filter response. Shown are the Model 1 and two graphs showing PSG and FM from the Model 2.
I'll send a pull request momentarily but if the code is not good let me know. I've never coded verilog before. I can make fixes and do a better request.
A test build is here. You CAN change the filter in the OSD but the option is below other options so it's off screen at first.https://drive.google.com/open?id=1vRdzuoXwtjKOkMn0tNoHpO63pTpDtuJN
Also I'm a git noob and I have to rebase. So the pull request will wait a little bit.
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