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.

I have just discovered that Apex Microtechnology of Arizona actually makes a chip, the SWR200 Precision Sine Wave Reference, to do much the same thing, a nice low-distortion sine wave with a ...