[Scali]

It was actually patented by Access Software, under the name of RealSound. https://en.wikipedia.org/wiki/RealSound

[djmips]

What a dumb patent. We were already doing this before their patent. We just ignored it and they didn't try to challenge. I remember talking to my EE father at the time and he said the idea of doing PWM for audio was obvious and ludicrous to patent.