The Commodore 264 machines, which include the Plus/4 and the C16 used the TED chip for video and sound. The audio capabilities were not great: two square wave channels. The Commodore 64’s SID chip on the other hand was a proper three voice synthesizer. So back in the day people built expansion cartridges for the Plus/4 utilizing the SID and eventually games and demos using this were published. These cards are pretty rare, but now there is a homebrew clone of the card!