C64 SID 6581 MOSFET NFT

The Commodore 64 sound chip MOS6581 also called SID, had a bug. It emits a “pop” setting volume level from 0 to a different value (it’s a 4bit register: max value 15). We are grateful about this bug because it was useful to simulate digital samples and voice in this home computer. This bug was exploited to implement a software 4-bit sampler and a simple speech synthesizer and most applications and games for C64 used this feature. In later versions of the SID the bug was fixed so digital sounds and voice in games were lost resulting not audibles.