Overview

Sonic CD's jump sound is infamous, so here's a hack that replaces it with the original.

This hack also restores the original skidding sound and fixes the bugged ring sound logic so that it can play in both speakers simultaneously, just like in Sonic 1, 2, and 3.

Technical Background

You might think that this was a simple hack to make. You would be wrong:

The reason that Sonic CD doesn't use the regular jump sound is because its sound engine lacks support for the audio hardware that the sound relies on - the PSG. Because of this, the sound had to be remade using the Mega Drive's other audio hardware - the FM. The PSG is a square-wave generator, while the FM is a sine-wave synthesiser, which is why the difference is so drastic.

Sonic CD uses the same family of sound engine as the other Sonic games (SMPS, also known as Sound Source), but its engine was extensively modified to remove support for the PSG and minimise RAM usage due to quirks of the Mega CD. I could have restored support for the PSG to this engine, but that seemed like it would be very tedious, so instead I settled for a more unconventional solution: replacing Sonic CD's sound engine with one from another Sonic game. For this task, I chose the sound engine from Sonic & Knuckles, since it's the closest match to the engine that Sonic CD uses.

What followed was converting all of Sonic CD's sound effect to the new engine, augmenting the engine to communicate in the way that Sonic CD expects, heavily optimising the engine to fit within the Mega CD's extreme RAM limits, and finally installing it into Sonic CD. All just to replace one sound. And you thought that this was a simple hack.

Usage

The hack is provided as a compressed 'CHD' CD-ROM image, which is compatible with Genesis Plus GX. If you want to burn this hack to a CD-R in order to play it on a real Mega CD, then you can use the 'chdman' tool to decompress it to a standard BIN+CUE combo.