Sonic 3 & Knuckles 'Robotnik's Theme' with intended drum sounds

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Yeah I know, this is quite the departure from my regular content... A more accurate (but longer) title would be "What would Robotnik's Theme sound like if the Genesis was able to play back drum sounds accurately?"

So what is this? The Sega Genesis (or Mega Drive depending on your part of the world) uses a Yamaha YM2612 and a Texas Instruments SN76489 to produce sound. The YM2612 has 6 channels of FM synthesis, with the sixth able to play back sampled data (some sound effects, but mostly used to play percussion) instead of FM. The SN76489 was much simpler - it had 3 channels that could produce square waves (this is the sound you think of when you hear "chip tunes") and 1 channel that produced noise (typically used to emulate a hi-hat's sound). Due to worry over its main CPU not being able to keep the YM2612 fed while also dealing with everything else, Sega also put in a Z80 chip to handle the sound driver. But it was a pretty old chip at the time, and periodically it needed to halt processing sound logic in order to load more sample data from the cartridge.

The YM2612's DAC channel just played back whatever value was last sent to it, so during these pauses it just repeatedly output the same value. As the game/sound logic wasn't aware of this, it ended up affecting the sound as a sort of time-stretch effect (lowering the pitch a bit) that also added some "crunch" and boosted the low frequencies. The pauses last around ~3.2 milliseconds and occur every 13.3 milliseconds or so. I'm not sure if this is a limitation of the Z80 or a limitation of the driver for it. I'm not sure if you could theoretically develop a faster/different driver that was able to play back a sample as recorded.

Looking at the waveform of the DAC channel, it also seems like there are much smaller pauses (as the waveform is stair-stepped), either due to the Z80 just not keeping up or due to devs adjusting pitch by slowing down how often it feeds a sample to the YM2612. Regardless, it dramatically reduces the high frequencies, such as the rattling or hiss of a snare.

Originally, I was just going to remove the pauses in the waveform and re-create it that way. But I was able to find some samples that look to have been created by someone who grabbed the original sample data from the ROM/cartridge and somehow figured out it's original sample rate (it was common for different samples to have different sample rates on Genesis games, and you could play back the same sample at different speeds, so the ROM data did not include a sample rate). These samples were very obviously the same as my 'recreated' samples, yet higher quality - you could hear the drumhead on the kick for example. So I ended up using those instead. These samples came from one of Ultima's replies on this thread: https://www.smwcentral.net/?p=viewthread&t=99680&page=1&pid=1515640#p1515640. Of course, I was hopeful to find the original samples that generated the drum samples (as in, before they were modified to fit in the very limited amount of space on the ROM), but I couldn't find a definitive answer when I was looking around.

I used VGMPlay and the Nuked-OPN2 YM2612 emulator to capture the sound with the DAC channel muted. I then used the ROM kick and snare samples to recreate the DAC channel and used Reason as the DAW to put them together. In order to compensate for the kick not being pseudo-pitch shifted (which moved the fundamental of the 'thump' lower and boosted low frequencies), I added a small low shelf boost to the kick. Drums should be approximately level-matched to the original drum volume.

I chose Robotnik's Theme as it was simple - just the kick and snare samples. The SN76489 wasn't even used for a hi-hat here, so it made for a great experiment to see if it was worth it. I dunno - I think it turned out pretty neat. What do you think?

If you found this neat, I HIGHLY recommend checking out @tssf's channel here https://www.youtube.com/user/tssf which is what sparked this idea. He has 'restored' the entirety of Final Fantasy VI's soundtrack and a ton of Chrono Trigger (and way more), using the same samples Uematsu/Mitsuda used to create the soundtrack before it needed to be modified to work on an SNES. It sounds incredible!

Видео Sonic 3 & Knuckles 'Robotnik's Theme' with intended drum sounds канала Sengin31