I've tried some Mega CD games of 2 different versions, one in original image size i.e. with 1411kbps wav or mp3, another with smaller mp3 files e.g. 128kbps. The problem is that the original larger CD image freezes on both Kega Fusion and Gens, even if I have activated "perfect sync". 2 examples are given below.
Lunar - The Silver Star
Version 1: 1 cue + 1 iso + 51 ape (total 245MB)
Version 2: 1 iso + 51 mp3 (total 50.6MB)
Tenka Fubu
Version 1: 1 cue + 1 iso + 18 wav (total 562MB)
Version 2: 1 cue + 1 iso + 18 mp3 (total 141MB)
I don't know if Ver 2 should be called a RIP version, coz they apparently include movies, bgm and se. If so, is there any way to run Ver 1?