Emulator

Game Name?
Sonic Mega Collection

Game ID?
GSOE8P, GSOP8P, GSOJ8P

MD5 Hash?
85a525df1481d0ad67d8761f832dca12

What's the problem? Describe what went wrong.

When starting any of the Genesis games, the sound slowly begins to lag behind the video until ~6 minutes, at that point the audio distorts horribly for around 20 seconds.

What steps will reproduce the problem?

Load game, load a genesis game, wait 6 minutes and the audio will sound bad, the bad audio will happen again in less than 6 minutes unless the z button menu was opened. Opening that menu will prevent the game from the desync.

It is important to make sure the bug hasn't already been fixed. Please tell us what the latest version you've verified the bug on.
I tested on 5.0-5139

Is the issue present in the latest stable version?
Yes, 5.0

What are your PC specifications?

i5 at 2.70, Windows 10, 8GB

Is there anything else that can help developers narrow down the issue? (e.g. logs, screenshots,
configuration files, savefiles, savestates)

I can trigger this exact issue on a real Wii if I use the homebrew loader devolution or nintendont. I am almost 100% certain CPU is not the problem, I tested the MIOS in Wii mode and the issue wasn't there. And on Dolphin I tested various overclocked settings, there was no change. I tested all DSP settings as well.

I wrote a gecko code for use on nintendont, that reduces the distorted audio to be less than a second, but the audio latency is still noticeable. More info and a video can be found here: https://forums.dolphin-emu.org/Thread-audio-patch-for-sonic-mega-collection