Ever wonder why your killer rock tune sounds big and huge while you're mixing it, but when you're finished you're shocked to discover it feels soft compared to other mixes, even though your meters are solidly lit? Think the latest whiz-bang level maximizer plugin will fix your problem? Think again. It could very well be that your problem isn't a dynamics issue at all.
Time for a rather broad statement: the high-pass filter (HPF) is your friend, and a very good friend indeed!
I generally put a HPF on pretty much most tracks except those that really have business being represented in the low-frequency range (bass guitar and kick drum, perhaps some keyboard pads, etc.). Most everything else gets its low end filtered to some degree. It is simple to do -- just open a 1-band EQ plugin (like EQ3 that comes with every ProTools system), set it to HPF with a 6dB/octave slope (for more subtle/general use), and sweep while listening to the solo'd track, starting at the lowest frequency, sweeping upward until you hear the timbre of the track change in a marked way. Then back the frequency down a bit to restore the naturalness of the presentation, and move on to the next track. (BTW, sweep without looking at the screen... just use your ears. You'd be shocked by what your eyes make you hear!) There are a couple of reasons for using the HPF like this:
- to restore lost headroom by removing unwanted low-frequency ("LF") content from tracks that don't benefit from it, and
- to add clarity and articulation to the true LF instruments in the mix
WIth regard to the first point, LF content exists in tracks that one wouldn't consider particularly low in tone. For example, most recorded guitar tracks, both acoustic and electric, include level-robbing LF content, and they would benefit from being filtered this way. Pretty much anything recorded up close with a cardioid microphone suffers similarly (as a result of proximity effect). When a track is solo'd, it may sound quite normal without the filtering, but when track after track of unfiltered midrange instruments begin to play together, all of this non-offensive LF information begins to stack up and robs your track of overall headroom, making the mix feel quieter, even when you're maxing out the meters.
By removing this unwarranted LF content you reduce the total energy (amplitude) of your mix (there's a LOT of energy in low frequencies, even subtle ones, particularly with the additive nature of stacking track after track). The decrease in overall level that results from the filtering give you greater headroom allowing you to push your faders up, making the mix feel louder even though the meters may now be reading the same as your 'quieter' mix before any the filtering.
Of all the mistakes I have made in mixing over the years, this is probablymy most egregious. It wasn't until I had been mixing for a few years that I really began to understand the value of preserving the headroom of the mix in this fashion. It really does make for a louder presentation when listening back.
The second benefit of this filtering approach of having removed this competing LF content is the elements of the mix that actually belong squarely in the LF domain (kick drum, bass, etc.) can now be heard and felt distinctly without having to use so much level (again restoring lost headroom). These LF components aren't being muddied and smeared by those same frequencies present in other tracks that didn't benefit from them, interacting and masking the important ones. It makes for more articulation of elements withing the mix... and with less effort, no less!
You will even find that there are occasions where you can get away with robbing quite a lot of LF from midrange instruments (guitars, bgv/s, etc.) to the point that the track will actually sound unnaturally thin when solo'd, but, because those same attenuated frequencies are present in other elements within the mix, the perception to the listener is that the overly filtered track(s), when blended into the overall presentation, still sound quite full and natural. Again, the more LF you filter, the 'louder' you can make your mix, because the less energy the mix contains, the greater your headroom, the higher you can push your faders up to reach the same absolute level on your outputs.
Play with this and see how much perceptively 'louder' you can make your mixes, without reaching for dynamics processors to squash your dynamic range.