Here’s a quick tip that will help you clean up your mixes and make them less muddy. Add a high-pass filter to every track. Yes, even bass and kick drum tracks.
The reason for this is that unwanted low-frequency information will quickly muddy up your mix. Even tracks like triangle and glockenspiel will likely have low-frequency noise that may be inaudible to you. If you’ve got 20 or 30 tracks in your mix, all this mud will build up and overwhelm your low end.
Because of the way our ears work, the low end data in your mixes has to be significantly louder that the highs and mids to remain balanced. Thus, most of the energy in a track will be concentrated in the low end. This means that compressors and limiters will react to this low-end data first, and if a large part of it is non-musical rumble and mud, this will adversely affect the way the compressor works. Cleaning up the low end will mean your compression will be more musical and thus will sound better.
I usually throw an EQ plugin on every track, even if all I use it for is as a high-pass filter. I highly recommend DMG Audio’s EQuality and EQuick, but any decent parametric EQ with a high-pass option will work. Solo the track, enable the high-pass filter and move it until you can hear the low end being removed. Roll it back just a bit so the track is no longer audibly affected and that’s it. If the EQ has a spectrum analyzer, you can turn it on to help visualize where the musical information starts. But even if you don’t see or hear any low-frequency noise, leave the filter enabled. Just a few decibels of mud on each track will add up and affect your mix.
On bass, kick, and other low instruments, I still recommend adding a low-pass filter. If the track relies on its ultra-low impact, set the filter at 20 Hz or lower, but many bass and kick tracks sound cleaner and clearer with high-pass filtering at 30-50 Hz.
As always, use your ears and do whatever sounds best to you. But if you’ve been struggling with muddy mixes, this tip can be a lifesaver!