if you want to take your overtones to another level,
he has a chapter on overtone exercises that i am currently
working through – i thought i could do overtones until i tried
out his various exercises which were difficult to start out,
but makes you really work/controll overtones.
The exercises he provides are the bsst i’ve come across.
But a word of advice you still need JF’s course to get the
overtones 1st, once you’ve got Through JF’s overtones course,
then Liebands shows you how little you are experienced in playing
overtones