[Mega Drive/Genesis] Phantasy Star II (All Official Versions)- Music glitch occurs when leaving town, missing and mangled instruments

[IVicViperI]

Version : Ares v131 & Ares v139
Options : Default
Game : Phantasy Star II (USA, Europe), tested both standard & Rev A. Japanese version also.
System : Mega Drive / Genesis

Every time you exit a town, the music instruments change/are missing compared to what it's supposed to be, and it doesn't occur when you start a save fresh from a dungeon or the overworld. It affects the entire OST.

Video demonstration attached to the message

PSII.AUDIO.ODDITY.480p.ver.mp4

Higher quality here: https://drive.google.com/file/d/1-wiEzacMy8KXa-S4E9vO-YVgYEWcTC9p/view?usp=sharing

This issue was present in the Sega Mega Drive Ultimate Collection on PS3/360 (Sonic & Genesis Ultimate Collection in US land) some 15 years ago to a greater degree, as even SFX in battles were altered and bordered on being very unpleasant. For the longest time, I thought this was supposed to be normal. On top of Ares, I know RetroArch through Genesis Plus GX doesn't fix it, neither do BlastEm, nor Kega Fusion.

However, there are recent official emulators that do fix the issue with this game: the collection called Sega Mega Drive (Genesis) Classics on Switch & PC don't have this music issue, although it suffers from very noticeable audio cracks. The game on Mega Drive/Genesis Mini 2 is apparently sonically perfect on top of having tons of quality of life improvements, it at least it doesn't have the music glitch.

While these use a different, modified ROM, the one dubbed PhantasyStar2_UE_GreenCrossFix.SGD in the Classics collection popped into Ares doesn't solve anything. So it is indeed an emulator related issue.

The US/EU versions use a different sound driver from the Japanese version. However, testing both the Japanese version and the US/EU ROM patched with a sound driver IPS modification also suffer from the glitch on Ares.

I've done so much ruminating these past few days and my mind's starting to go in a bad place as I've seen barely any documentation online about this. At this point I'm starting to even wonder if it wasn't borked the same way on original hardware too and recent official emulators by Sega magically solved the issue.

[LukeUsher]

I do have to wonder if it's possible behaviour differs on different revisions of the Mega Drive hardware; kind of like how early GEMS games (like Earthworm Jim) have music playback issues on some consoles but not others...

Either way, this needs real hardware testing.

[remutro]

It may not be that ROMs were modified in re-released versions. They could easily be using something like Lua scripting to modify the game during runtime to address previous issues. Considering how many emulators (and really good emulators) this impacts then as Luke has already pointed out, this needs to be checked on real hardware.

[IVicViperI]

I could eventually test it out on real hardware to report my findings, since I have a PAL UK Mega Drive Model 1 with region and 50/60hz switches lying around in one of my boxes (1601-05, seemingly board VA 6.5 looking online, if that means anything), though I don't have a genuine copy of Phantasy Star II. They fetch for some horrific prices on ebay, I still remember when I could find the cart for 5-10€.

Would an Everdrive or any other flashcart do the trick and not affect anything? I'm kind of tempted to get my MD out the box and buy a flashcart next month just for the experiment.