I use the C1 in unlinked mode occasionally to master... with just a touch of compression (needle barely moving). I know some of the high end guys use modified SSL type circuits, but who knows what's under the hood (B.B. Brian, etc.). The C1 is definitely not "pristine", though... alot of grit in there. I do like the fact that it will do an unlinked dual mono thing. I know some folks feel the attack/ release times are not ideal for mastering, but on hip hop, or uptempo rock stuff I think it can work great. 90% of the time I'm using an STC8 though, and not the C1.