Hmmm... So you're saying that it's probably just s(M)exscope showing it to me that way even though it's probably not going into Line-In of the computer like that?
If you look at an image of the actual audio recorded when I turn the pot that modifies the pulsewidth it also looks like that.
https://sdrv.ms/146yF34
I'm just using an old computer to experiment with. I wouldn't want to plug in into my real Echo soundcard so maybe it's just something strange with the onboard audio on that machine.
Maybe I'll install an actual soundcard in that old machine and see if it looks different.