Earthworm Jim: Earthworm Jim Sound Bug Fix

An obscure bug in the sound driver causes the music and sound to malfunction slightly on Gen/MD hardware that has a discrete YM2612. This patch fixes the stuttering sound and music that can occur on a Model 1 Genesis or Model 2 with a YM2612. It also adds in a cheat code for a new sound test function and removes the region protection. This patch is mainly intended for flashcart/Everdrive users with Model 1 consoles.

Earthworm Jim sound bug fix & bonus sound test
----------------------------------------------

This patch applies to the USA version of the ROM. This patch is mainly targeted
at flash cart/Everdrive users who are playing on older Sega hardware and
requires some explanation.

Sound lag bug fix
-----------------
An obscure bug in the sound driver causes the music and sound to
malfunction slightly on Gen/MD hardware that has a discrete YM2612. This is
most evident during the intro of the "New Junk City" music where there is an
audible stutter toward the beginning of the song, but it will also come up and
cause the music and sound to glitch any time there is an FM pitch bend and a
digital sound playing simultaneously. This happens fairly often in EWJ because
most of the game's sound effects are digital sounds. This notably doesn't happen
on any emulator or any console (that I own) with integral YM3438 (most model 2
Genesis/MD).

Integrated sound test
---------------------
Pausing the game and entering the code A,B,B,A,C,A,B,B will take you to
a new, custom sound test screen to listen to the game's tunes. Note that this
will take you out of your current game and exit to the Sega logo when you press
start. I spent way too long on this.

Region lock removed
-------------------
US ROM now works in all regions. This took about 2 seconds.

Technical information
---------------------
The sound bug was eventually fixed in GEMS 2.8, but comparatively few games use
this version of the driver. The fix was applied by porting the original sound
data to GEMS 2.8 and patching in that version of the driver.

Relevant excerpt from GEMS 2.8 documentation:

"2) The now famous "GEMS slows down and stutters when the Genesis is cold
and I mix samples with pitchbend" problem appears to be fixed. If you
see this problem again, please inform Sega at the number above."

In my testing this is only partially correct and doesn't seem to have anything
to do with the Genesis being warmed up, but it only reliably occurs on YM2612
equipped consoles. For me, this happens on both a non-TMSS model 1 and a VA3
model 2 console, and the problem is much worse on the model 1.

The bug does appear in other games, but is usually less noticeable as it doesn't
happen quite as often, or the games themselves are more obscure. For some reason
quite a few sports games that use GEMS suffer from this (NBA Jam, NFL '95 for
example).

Dustin
https://www.youtube.com/user/DUSTINODELLOFFICIAL
http://www.romhacking.net/community/4927/


Database match: Earthworm Jim (USA)
Database: No-Intro: Genesis (v. 20180824-045026)
File/ROM SHA-1: A544211D1EBAB1F096F6E72A0D724F74F9DDBCE8
File/ROM CRC32: DF3ACF59