Exactly where is the ''jitterclock '' located ?

I have pretty good seperate components in a transport and d /a convertor.....I understand for the most part, the need for islolation and or de-coupling on a transport and agree that whatever you like to use is your choice in using either points, cones, feet, platforms with and without air.....etc., etc.,....but I had an audiophile just tell me that the d /a is JUST as important in using stuff to kill all vibration and airborne attackers...'cause that's where the ''clock'' is....Huh ?....well, should I spend some dough to put some of this stuff under a heavy solid state and also reputable d /a convertor ? I would if I knew that it really would make a difference.