[pezezin]

> I think the article is sorta wrong about the sound setup, the Mega Drive I does have a sound input on the expansion port, and mixes it into its sound output.

The Megadrive has a stereo sound input on the cartridge port too, for a total of 3 stereo sound sources (the YM2612, the MegaCD, the cartridge) plus one mono source (the SN76489 PSG).

As far as I know no original release ever used the cartridge input, but nowadays it is supported by many flashcarts to emulate the MegaCD or to provide CD quality audio tracks (MSU-MD and MD+ romhacks), and it has been used by some recent games.

[ndiddy]

The 32X used the cartridge audio input for its PWM audio channels. For one example of how this worked, Knuckles' Chaotix used the extra channels for the percussion in its music: https://www.youtube.com/watch?v=L6BSQVK9gSc

[pezezin]

I always though that the audio mix happened in the 32X itself, much like the video mix, but I just checked the schematics and you are right (page 7 of https://segaretro.org/File:Genesis32XUSManual.pdf)

I have a Japanese 32X and a copy of Knuckles Chaotix, but I have yet to play it so I didn't notice the sound xD