tapevulture Aaah, that’s putting one channel out of phase with the other for a dissonant effect that you’d very rarely want to produce on purpose.
If you did it with exactly the same signal in each ear (albeit phase-reversed) then they’d sum to actual silence (-1 + 1 = 0), but the other instruments and sounds in each channel get in the way and cause only certain frequencies to be phase-cancelled. Your brain knows something’s up and that’s what causes the sensation.
I disagree that the Genesis / Mega Drive didn’t have that capability, as it was capable of stereo sound, PCM playback and wave synthesis so I don’t see why it couldn’t. While the audio hardware is technically only capable of a single PCM channel, you could technically add another in software using the CPU. Not sure if any games actually did this but I’ve seen demos and homebrew that did.
As far as I can tell, the Vapor Trail example is just delays and clever panning.