I've heard a lot about high-pass filtering tracks to reduce clutter at mixdown, but not as much about low-pass filtering in this context. Would mixes suffer or benefit from doing the same at the opposite end? For example, would it be easier to bring out 'air' in a vocal if other parts were low-passed?
Via SOS web site
SOS contributor Mike Senior replies: Particularly in small-studio environments where the low-frequency monitoring fidelity is questionable, there's a lot to be said for high-pass filtering in a fairly systematic way to head off problems at mixdown. However, widespread low-pass filtering offers fewer benefits, simply because so many instruments in a mix will have harmonics and noise components that extend right up the spectrum. In practice, I find peaking/shelving cuts are, therefore, more appropriate for dealing with typical mixdown tasks, such as frequency-masking problems. Yes, in theory you could make your lead vocal sound airier by low-pass filtering the other parts, but you'd still have to consider how the mix as a whole will sound during moments when the vocal isn't active, so achieving an airy vocal in practice isn't usually as simple as this.
Having said that, there's nothing wrong with low-pass filtering if you really want to kill the high frequencies of an instrument for balancing reasons. I would most commonly do this with amped instruments, such as electric guitars, which are capable of contributing a lot of undesirable amplifier noise in the top two octaves of the audible spectrum. However, this has to be evaluated on a case-by-case basis, because it's very easy to dull the overall mix if you're not careful.