Spectral morphing resynthesis

I stumbled across this online and cant find much about it, the main example I found was using kyma tau editor to morph sounds into one another. I think its pretty cool but A. Im not looking to spend £3000 to try it and B. While the effect is obvious I dont really understand what is going on. How exactly does it work? I found the more affordable mmorph by melda but id still like to know more first. Can anyone chime in? Any other options out there too?