STTR is based on CCRMA's work, combined with my other experimental results.
It is a granular effect, but many grain parameters are fixed and not adjustable.
Basically, it produces additional harmonics on top of the original spectrum; their frequencies are controlled by Hop, and their amplitudes by the window function.
Through reverse/forward playback, the additional harmonic frequencies move inversely/forwardly relative to the original frequency, similar to piwarp / ring modulator.
short-time time reversal (or not)
simple formant shifting (behaves like formant shifting with a short hop, and more like pitch shifting with a long hop)
more flexible window function to shape the spectrum