Sure, Sean. I'd be happy to address the first part. But I'm not going to pretend to be an electrical engineer by explaining exactly how a line-conditioner does what it does. That is, so long as you promise not to pretend either. :)
How I would describe what a 'proper' line conditioner attempts to do includes the following:
1) A well designed line-conditioner attempts to dramatically lower the noise floor revealing tremendous amounts of true, subtle, low level musical detail. This detail that was previously masked has a tremendous impact on the ability of the listener to connect with the music.
2) A well designed line-conditioiner attempts to reduce AC noise by removing the A/C RFI and EMI noise that is ubiquitous in every system to various degrees. These noise artifacts have the effect of artificially highlighting frequencies where the noise manifests itself. Also, the noise artifacts are amusical and instead of these frequencies adding to the musical experience, they cause listening fatigue and unnatural listener tension that ultimately reduces and more often eliminates the ability of the listener to connect with the music. Classic manifestations of this type of noise are unnatural/negative vocal sibilance not present in the original recording and distortions on crash cymbals and high hats in drum kits. The presence of external A/C RFI and EMI noise causes these sibilances and cymbals to separate from the musical tapestry and they appear to separate from the soundstage. They are so easy to pick out once the phenomena is pointed out that even casual listeners can pick them out with ease. Because these distortions are errors of commission, where the noise floor effect discussed in a) above is an error of omission, they are, for me, the greatest reason that a system fails to communicate the musical message.
3. A well designed line-conditioner attempts to induce no sonic harm of it's own. ie the rather common suppression (rolled off) of offending frequencies as you implied above.
4. A well designed line-conditioner attempts to avoid being the bottleneck with regard to current limitations.
5. A well designed line-conditioner attempts to provide bi-directional noise filtering. A tremendous benefit for anyone using a cdp since the digital noise generated will most always inject digital noise even all the way back into the service panel and hence contaminate other components if left untreated.
6. A well designed line-conditioner attempts to best utilize a one line-conditioner per component only. Surely this is the most effective way to keep noise from contaminating other components as well as the optimal way to take full advantage of dedicated circuits/lines.
I hope this helps educate you a bit regarding 'proper' line-conditioning. If you have any other questions, you know where to reach me. :)
-IMO
