Bear in mind that this is strictly an audio comparison. I recorded no video from the units themselves and what's on-screen is recorded from Kega Fusion and synchronized to the best of my ability, and the emulated game plays slightly faster than the real thing so it will go off-sync from the recorded audio now and then, so please excuse any slight errors in synchronization. I wanted to compare gameplay audio so you can hear how it actually sounds when you're using the system and figured the easiest way would just be to record the initial demo of a random game. Figured Sonic 1 would be best, since everyone knows and loves Sonic 1. You love Sonic 1, right?
This is essentially the prelude to my coming video comparison of most Sega Genesis variants. I say "most" because I'm simply limited to what I own and I don't own every single variant of every single model of the Genesis (I'd be shocked if somebody actually did!) but I'm covering pretty much every base here in terms of North American Genesis sound capabilities. Whether there's any difference between North American, Japanese, and European units I really don't know; I don't imagine much, if anything.
Anyway, as many know, there are several models of the Sega Genesis, but aside from the physical appearance of the console, there are many internal changes between each model; some good, some bad. Not only that, but there are several variations of each individual model as well. This thread on Sega-16 provides much better insight than I can on this subject:
http://www.sega-16.com/forum/showthread.php?7796-GUIDE-Telling-apart-good-Genesis-1s-and-Genesis-2s-from-bad-ones
Unfortunately there don't seem to be many comparisons on just how different each version of the Genesis sounds, and what few there are simply seem to compare the non TMSS model 1 Genesis with the full motherboard model 2, usually mistaken that it represents all model 2s. So, while the video more or less speaks for itself I figured I'd voice my own opinions on each model.
First off at 0:00 is, of course, the original model Genesis with the legitimate YM2612. This is generally regarded as the best sounding variant of the system...and it's true, for the most part, but it isn't perfect. The original models seem to have this issue with notes sometimes "hanging" in the background after they end. It's difficult to explain and, to be honest, not very apparent in this comparison, but usually when a note stops abruptly you'll hear a faint echo for a second or two. If you pay close attention you can hear it in this video but it really doesn't become obvious unless there's not much going on in the song. Either way, this is definitely the nicest sounding model of the bunch even with that small setback (A setback that, in some games, it takes advantage of, but more on that later). Audio is very clear and the bass is very heavy with only a little bit of distortion happening when things get a little too loud. This is the original hardware so, naturally, it is the best.
Now this is where things get shaky. Around 1991 when Sega started bundling Sonic 1 with the Genesis they changed the design of the model 1 to add the TMSS BIOS screen (The "Produced by or under license from Sega Enterprises Ltd." boot screen that we're all familiar with) and practically ruined the audio of the system alongside it. I don't know the exact circumstances or dates behind it but these "bad" motherboards exist in both models that say "High Definition Graphics" above the cartridge slot and ones that have no text on the cartridge slot. It can be difficult to tell good ones from bad ones just by looking, but the majority of "High Definition Graphics" should be non TMSS, but there's a few bad ones out there; the opposite is true of the non "High Definition" models: most bad, some good. The ports are different between the two and you can check the previously linked Sega-16 thread for specifics and pictures.
Now, I don't actually have that specific model so I'm just going to skip right to the model 2, of which there are two major variants of: One with a motherboard that gets cut off at about 3/4 of the case and another with a motherboard that covers the entire case, hence the names. I don't know which came first or if they were both produced simultaneously. All I know is that the 3/4 model 2 I have is from Christmas 1993 and is a Sonic 2 bundle, specifically. Whether those details matter I really have no clue. Anyway, at the 0:50 mark comes that sample. As you can hear, it is definitely more muffled than the original model, but the bass is very much still intact, the audio is less distorted and that issue with the "hanging" notes is gone. Overall this is a very nice sounding system and -- while this is likely nostalgia talking -- definitely my preferred model of the Genesis for playing games. Despite the slightly muffled audio in comparison to the model 1 it makes up for it with the improvements over the original's setbacks. Well, that and you don't need to use a hodgepodge of cables in order to get stereo audio out of it. I think objectively, however, the non TMSS model 1 is best. I grew up with this model in particular, though, so there's that.
Next up at 1:39 is the one everyone knows. The worst of the worst: the full motherboard model 2 Sega Genesis. Rest assured that every bad thing you've heard about it is true. This thing is abysmal and I feel terrible for anyone who had to grow up with this one. Audio is ridiculously distorted to an absurd level and everything is just so ridiculously loud on this thing. Keep in mind I did not do any volume adjustments with these models. This is really how this system sounds at every volume level. It's distorted, fuzzy, icky, grimy, and if audio had an odor, smelly. If you ever want to pick up a model 2 Genesis, avoid this one at all costs. It's very easy to avoid this model if you're looking at it in front of you. Flip it upside down; if you can see the motherboard under every vent of the system, it's a dud. If the motherboard gets cut off an inch or two before the vents end, you've got the good one. Unfortunately most people listing their system online don't post pictures of the bottom, so if you're in the market for a Genesis and see a cheap model 2 listing, ask them about the bottom of the console and you might get lucky.
Next up at 2:28 is the Sega CDX, the combined Sega Genesis and Sega CD in one convenient unit. Audio sounds very clear but, man, there is practically no bass on this thing at all. It feels very empty without it. Definitely not bad, but very...flat.
After that, at 3:17 we have the JVC X'Eye, the...other combined Sega Genesis and Sega CD! Essentially, due to a contract agreement after JVC manufactured the sound chip on the Sega CD, JVC were granted the rights to produce their own model of the system. In Japan this is known as the Wondermega and was released with S-Video and MIDI ports right on the system itself. Its disc tray was decked out and fully motorized with red and green lights on the side and is by far the best looking version of the Genesis and of any game console for that matter, in my opinion. Later the Wondermega got a revision that removed the fancy motorized disc tray and lights but with a wireless controller port. They used this as a basis for the American model, but removed the S-Video and MIDI ports as well as the wireless controller port replaced with the standard wired one. In essence we got a watered down version of an already watered down console, but the wired control port is definitely a plus over the wireless one.
Er, anyway, about the sound on this, it's basically the same story as the CDX: Clear sound, very little bass, except this one takes it to another level. This thing sounds tinny. It's a real shame. It sounds very nice aside that fact, too. It really doesn't sound too bad if you're just playing it without a care, but when you listen to one of the better models and go back to the X'Eye, the difference really kicks in. Overall I'd say this one has it the second worst out of the ones that sound good. Definitely acceptable, though.
After that at 4:06 is the Sega Nomad, the portable Sega Genesis. And yes, it has the real hardware! Aside from general noise that the system outputs, the soundchip itself sounds very, very good. I'd put it right below the 3/4 model 2 variant. Very impressive for a portable system from 1995.
Lastly at 4:55 is the Genesis 3 manufactured by Majesco in 1999. The audio on these things is, surprisingly enough, not that bad. Not incredible but definitely better than the non TMSS model 1s and full motherboard model 2s. Bass isn't too heavy either but it's definitely a passable unit for something that wasn't even manufactured by Sega themselves. However, there's a huge setback: it only outputs mono! No clue as to why, and the really irritating thing is that even if you've got this hooked up with a stereo A/V cable, it'll only output the audio to one speaker rather than splitting the mono audio into both. Very annoying, but the Genesis 3 is a novelty at best anyway, so there's really not a whole lot to complain about.
After that at 5:44 I figured I may as well show off how the emulated sound is. It's very clear, but almost too much so. Again, bass is lacking and everything on the whole just sounds not as it should. I suppose that's what happens when you turn an analog synthesizer into something digital.
Now the interesting thing is that Kega Fusion has a sound filter that emulates how the system should actually sound, shown at 6:34, and it's good. Damn good, in fact. It's almost difficult to distinguish it from the real thing. It comes very, very close to sounding like a mix between the Non TMSS model 1 and 3/4 motherboard model 2. Whoever made this did a fantastic job. A lot of care was clearly put into it.
Anyway, that covers everything I have at the moment. There's more to come after this. I've got a few other comparisons to make with strange issues between systems with specific games and general emulation errors, among other little oddities. That will hopefully come soon, and even more hopefully with a much shorter description.
In any case, the world of Genesis sound can be very confusing and I hope this sheds some light on the strange issue of Genesis sound.
This may well be the longest description a video on Youtube has ever had. So much so that I had to link it off-site. I am truly sorry.