I've read a Topaz Isolation transformer with a 0.0005 pf rating can have a common mode noise reduction of -146 db. The pf rating seems to determine the noise reduction. How low can you go with common mode noise reduction to reach the noise floor or until it is inaudible to the human ear? Can you get -300 common mode noise reduction? I don't know if it has any differential mode noise reduction. I think what people need to look for is the curve on a graph of the common mode and differential mode noise reduction within a range of frequencies if possible. The problem is I don't know how these frequency ranges affect digital and analog gear separately. Also how do these transformers affect the sine wave?