APU enhancement

[fjpolo]

[APU]

• Improved R2A03 APU’s triangle wave and made its mixer linear.
• Improved mapper VRC6’s sawtooth wave. Mixer is already linear.

[VRC6]

• Added mapper. Tested on Castlevania III (Japan). Needs more testing.

[Mapper4/69]

• Disabled APU Enhancement because volume levels saturate

References:

• https://www.youtube.com/watch?v=8RrQrATnXXY&t=500s

[fjpolo]

APU sounds broken in Little Sisyphus.nes if Enhancements are disabled, also with Celeste Mario.nes

Edit: found a few bugs that I need to fix

[nand2mario]

Can you remove the firmware here and add a separate PR for the firmware in the snestang repo? Let's keep the firmware in a single repo (snestang) for now and make sure the same firmware works for both nestang and snestang. CORE_ID can be used to determine which core is running. In the future we can set up a separate repo for the firmware.

[fjpolo]

Can you remove the firmware here and add a separate PR for the firmware in the snestang repo? Let's keep the firmware in a single repo (snestang) for now and make sure the same firmware works for both nestang and snestang. CORE_ID can be used to determine which core is running. In the future we can set up a separate repo for the firmware.

Will do, this way it will be cleaner. Adding a separate repo has the advantage of adding it as a submodule.

Edit: if you create an empty repo for the firmware, I can fork it, create a separate branch to add firmware/ as submodule and create a separate PR for it.

[nikitalita]

Does this implement the suggestions from this video? https://www.youtube.com/watch?v=8RrQrATnXXY&t=500s

[fjpolo]

Does this implement the suggestions from this video? https://www.youtube.com/watch?v=8RrQrATnXXY&t=500s

Oh yes, that's the idea! I watched that video a long time ago and yesterday came back to my mind.

I'm still on it though. I missunderstood how the module worked so I made some mistakes.

Will change the draft to a proper PR after fixing, testing, and removing firmware/ dir to have aclean PR

[fjpolo]

Results are sadly not as good as I'd like :( but at least enabling APU Enhancements gives the user a linear mixer, for those who'd prefer it :)

Edit: Slept on it and I think it's not ready yet. Will keep tinkering

[fjpolo]

After shifting Noise Channel output from 6bit to 8bit, it soudns better, at least for me.

[fjpolo]

It's finally working as expected. PR contains files from Cheats PR because I rebased form there

[fjpolo]

Will be added in #88