the Twin-T notch filter, that turns out to be sharp enough to build a sine-wave oscillator on, and tweakable enough that we’ll make a damped-oscillator drum sound out of it. Here’s a quick ...

Sine-wave speech can be thought of as a sort of auditory illusion, a sensory edge case in which one’s experience has a clear “before” and “after” moment, like going through a one-way door.