AGEMAME HQ

While trying to emulate the MPU4 and M1 platforms, you start to wonder why certain games seem to have significantly poorer sound than others. Suddenly it dawned on me that these supposedly generic hardware units were in fact different in many key areas.

In the case of MPU4, one of the modifications was to remove the original audio chip from the main board (an AY8913), and instead have the sound generation placed on the ROM card. It looks like there were two cards in use, one with a Yamaha synthesiser chip, and one with an OKI MSM6376 ADPCM player, which were then used.

However, I’m yet to find out just what replaced the AY chip on the main board, and many games produced after the modification continue to write something to it, hence the garbage audio in Connect 4.

So basically, we have another minibeast to contend with - as the video hardware and Connect 4 are written for two different revisions.