Gold said:
A 16K 18dB/oct lpf is probably on most records you hear.
Yep and I had to learn that lesson the hard way when trying to cut Van Gelder Blue Note records at almost full frequency...Those recordings are a lot brighter off the tape.
***for those who are interested, a cutting lathe has a harder time cutting high frequencies than low frequencies. The coil in the cutting mechanism will heat up with a lot of high frequency content. Filters and de-essers are used heavily in cutting. A sustained 10K tone even at 0dBu would burn out the coil.
Regarding filters in digital mastering, if using them creatively, the steeper slope will have more of a resonant peak at the filter frequency and have more of a "sound". So there's really no definite answer to that. Just start at 6db/oct and start getting steeper until you get to where you want it to be.
But if your fixing something, its always going to be a compromise between taking the "broken" sound out and keeping the original sound as close to what its supposed to sound like. Again no definite answer, just start at 6db/oct and go up.
Regarding mid/side I have always found peaking eq (cutting) to work better than filters. Like crashing cymbals, I will sweep around in the sides with a medium Q dip until I find the loudest part of the offending frequency and cut there.
There are also some powerful mid/side multi-band compressors out there that allow you essentially do the same thing as with the eq but dynamically.
Just use the force Luke