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It may be because you're not running the channels in full blast. For example PCM is 12...18db more quieter than FM at full blast and games are thus using low enough volumes on FM so that PCM is not overshadowed.
Also, I have noticed thato n MD1 the PCM is much more noisy than on MD2. So I guess there is a design flaw somewhere.... ?

MD2 certainly does not have any of those features... sound is crisp and clean, and rather close to what emulator would produce.

TmEE wrote: Also, I have noticed thato n MD1 the PCM is much more noisy than on MD2. So I guess there is a design flaw somewhere.... ?

As far as I know, the MD2 has an integrated chipset which merges the YM2612 with the VDP, so chances are high that they reworked the chip design. I never had a MD2, so unfortunately, I can not comment on this.

MD2 certainly does not have any of those features... sound is crisp and clean, and rather close to what emulator would produce.

If that's the case, then the distortion effect would have to be made optional in an Emulator, or simpler, let the user choose between MD1 and MD2 configurations. However, I doubt that any game released before 1994/95 takes the non-distorted sound into account.

I wonder if the CMOS version of the YM2612 (YM3438) has the same design flaw, or if Yamaha fixed it. In theory, they should be swappable. Have to get my hands on a System 18 board...

I had a chance to listen a recording from a YM3438 chip in a MD1 and it sounded identical when it comes to noises etc. My firend had to rework the input stages of the mixer though as the output is different form YM2612 (higher impedance).