Sound Speed (What is it?)

After a few days of trying the demo I'm incredibly impressed with pianoteq and will probably buy.

Something I'm a little confused about is the "sound speed" control. I notice that it does effect the sound quite radically, but what I would like to know is a little bit more about what is exactly happening regarding the sound processing. For example, does it effect stereo image at all? And what are the distinctions in the way it functions with the differences between the mic, the binaural and the stereo set ups?

Any information will be welcomed.