Is dht derived from total t or free t. that is, does the conversion occur before t is bound to shbg or is it the unbound t that is converted. ?

Bioavailable T: Testosterone that is bound to shbg is not biologically active and therefore does not participate in conversion to dht. Free t and t bound to Albumin are biologically active (bioavailable) and is converted to Dht in various tissues throught the body. Why do you want to know this?

Neither: Testosterone becomes DHT within cells themselves. There is a great deal of junk written about this molecule, especially because of its link to male pattern baldness. I'd encourage you to ignore all the "pop" stuff -- everything in your body affects everything else, and ultimately a healthy, fitness-focused lifestyle will be much more helpful than anything else that might affect DHT. Best wishes.