Thanks for all the info guys, I will read about FFT and all that. I hope it will answer my wonders as to why there is no vibration in sound.

As for JACK support.... would anyone be interested in adding it, if it is trivial? Would love to have it in my audio chain.

As for real time stretching, this is not necessary - it does react to parameter change with a slight delay, but it is ok.

Louigi.