Given the pitfalls faced by both pros and amateurs, Wes is correct in observing that it's a miracle that recordings get made at all. As a rank amateur, I'm fascinated that even with twenty first century technology, putting together any sort of acceptable recording is still so much an art. While my copy of "There Lies the Home" is still en route to me, I'm willing to believe Wes that I'll neither be able to hear the whoosh of the vacuum cleaners in it nor will I be aware of the passages where John filtered it out.
The use of filters is, for me, an exercise of iterative "guess and try". Sure, in addition to hearing it, I can get a spectrum analysis of the piece of the file that contains the noise, but the final decision regarding the range of operation and the slope of the filter is based on what "sounds right" to me. I preview one setting after another until I settle on what I decide is the best combination of noise elimination and preservation of the continuity of the musical content. Given the limitations of my own knowledge and experience and those of the tools I have, that really is the only approach available to me. Since I'm a devout subjectivist, I have no problem with it. JA, on the other hand, is certainly an adept practitioner of measurement - usually armed with data to help define what he hears. Some of the rest of you, I'm sure, are also better at measurement than I and more likely to rely on it. I wonder, when you are forced into filtering, do you also end up with "guess and try" and what "sounds right" or do you have some other - perhaps better - answers to dealing with unwanted noise?