Genesis Plus GX, Where is the Audio Lowpass Filter?

Great catch! Indeed the vibrato has less range with Nuked-OPN2.
In this case Mame core sounds like the hardware, while Nuked has a bug.
I will report to nukeykt about this bug ASAP.

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I think it is fixed now, but still not merged.

Meanwhile here is a comparison of Model1 VA6 vs Model2 VA4, both considered best in their model number.
Model2 is MUCH more filtered!
Hopefully one day GPGX will have the option to choose between first and second order lowpass filtering so that the user can choose freely… it wouldn’t hurt if I ask ekeeke to add second order filtering.

Streets of Rage 2 is about half way, but all the video provides good example of the filtering order and how it compares.

There is another option YM2612 DAC quantization. What is it and should it be on or off for maximum accuracy?

“YM2612 DAC quantization” should be ON to quantize from 14bit to 9bit like the real chip does.
The result is ADDed dithering noise while the FM channels are playing.
Without it, the FM emulation is crystal clear and some games might not sound correctly which rely on that added noise from the chip.

To hear what this option does;
Streets of Rage 2 - BGM 10, intro.
Listen with headphones and switch the DAC option On/Off.

Here is BGM 10 on a real Model1 VA1:

Note the emulation is not perfect and still is much cleaner and less distorted than the hardware YM2612.

The DAC noise is the biggest difference between the YM2612 and YM3438, with YM3438 being the newer and quieter variant in the Model2 with much less noise than the original discrete YM2612 in Model1, but the quantization to 9bit is the same on all models, so the DAC option in GPGX should be ON.
This difference in noise is one of the differences in audio between Model1 and Model2, but the Model2 had badly engineered amplification circuitry after the clear YM3438 which made it sound distorted, that’s why many people modify the Model2 with “Mega Amp” circuitry which replaces the miss-engineers circuitry with a proper one.

More info here:

Okay so to make sure I got this all correct, to get that Model 1 Genesis sound the settings should be

YM2612 DAC quantization - On

YM2612/YM3438 core - nuked opn2

Audio filter - low-pass

Sound output - mono?

Actually, you should wait for the next build, we’re all in for a big treat!
NukeYKT has fixed all the bugs and added accurate DAC quantization and “Ladder Effect” emulation to his cores.
Basically, it is the first OPN2 emulation that sounds exactly like the hardware including all the noise and distortion of the YM2612 DAC.
“DAC quantization” option applies only to the Mame core, Nuked cores have everything already included.

He included three new options for the Nuked-OPN2 varitions:

  1. YM2612
  2. Asic YM3438
  3. Discrete YM3438

Here are some examples where there is clear difference.
In the archive I included my Model1 VA6 recording and all new OPN2 core variants.
The clips have been professionally recorded and normalized to be same volume.

Aladdin: listen for intro noise and 16sec note stops tail quantization.
Konami Logo: listen for music end tail quantization noise.


Can’t wait, so glad this stuff is being taken care of.

Here’s test build compiled by nukeykt:
Rename the proper version to genesis_plus_gx_libretro.dll


Great improvement!!! The DAC emulation of nukeykt is very impressive!!!

By the way, I have 2 questions:

  1. The lowpass filter is present in the Model 2 with ASIC YM3438 or only in the Model 1?
  2. The lowpass filter affects the CDDA audio of Sega CD in the real console?


  1. Yes, it is even more filtered than Model 1.
  2. No.

so the bug fixed core still isn’t merged, is it? Just tried the latest Genesis Plus GX core, and the vibrato in Castlevania is still incorrect.

What is the best setting to have the Model 1 sound?


What if I’m using GPGX to play Game Gear and Master System games, should I disable the lowpass filter?

YM2612, Stereo, Low-pass, 55.


If you used to play with a Master System Converter (or Everdrive) on the Genesis, then keep it On.
The hardware Master System just like NES did NOT have a lowpass filter, so turn it Off for authenticity.


DAC quantization should also be ON right? Or is that setting MAME only?

DAC quantization is for Mame core only.
All the Nuked cores have all the proper emulation of the electronics already.

So with the most recent core update, there are now 3 different nuked soundcores (ym2612; asic ym3438; discrete ym3438) Which one is the one to go for most authentic model 1 sound?

Three posts above I answered just that…

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Thanks. So what are the two others for then?