Perhaps the most difficult task of a mixing engineer is balancing the bass and drums (especially the bass and kick). Nothing can make or break a mix faster than how these instruments work together. It’s not uncommon for a mixer to spend hours on this balance (both level and frequency) because if the relationship isn’t correct, then the song will just never sound big and punchy.
Here's an excerpt from The Mixing Engineer's Handbook to help you achieve this sometimes mysterious balance.
"In order to have the impact and punch that most modern mixes exhibit, you have to make a space in your mix for both of these instruments so they won't fight each other and turn the mix into a muddy mess. While simply EQing your bass high and your kick low (or the other way around), might work at it’s simplest, it’s best to have a more in-depth strategy, so to make them fit together, try the following:
1. EQ the kick drum between 60 to120Hz as this will allow it to be heard on smaller speakers. For more attack and beater click add between 1k to 4kHz. You may also want to dip out some of the boxiness that lives between 200 to 600Hz. EQing in the 30 to 60Hz range will produce a kick that you can feel if your speakers are large enough, but that can also make it sound thin on smaller speakers and probably won’t translate well to a variety of speaker systems. Most 22 inch kick drums like to center somewhere around 80Hz, for instance.
2. Bring up the bass with the kick. The kick and bass should occupy slightly different frequency spaces. The kick will usually be in the 60 to 80Hz range whereas the bass will emphasize higher frequencies anywhere from 80 to 250 (although sometimes the two are reversed depending upon the song). Before you continue to EQ at other frequencies, try filtering out any unnecessary bass frequencies (below 30Hz on kick and 50Hz on the bass, although it varies according to style and taste) so the kick and bass are not boomy or muddy. There should be a driving, foundational quality to the combination of these two together.
A common mistake is to emphasize the kick with either too much level or EQ and not enough on the bass guitar. This gives you the illusion that your mix is bottom light, because what you’re doing is effectively shortening the duration of the low frequency envelope in your mix. Since the kick tends to be more transitory than the bass guitar, this gives you the idea that the low frequency content of your mix is inconsistent. For pop music, it’s best to have the kick provide the percussive nature of the bottom while the bass fills out the sustain and musical parts.
3. Make sure the snare is strong, otherwise the song will lose its drive when everything else is added in. This usually calls for at least some compression (see Chapter 9 on Dynamics). You may need a boost at 1k for attack, 120 to 240Hz for fullness, and 10k for snap. As you bring in the other drums and cymbals, you might want to dip a little of 1k on these to make room for the snare. Also make sure that the toms aren't too boomy (if so, try rolling them off a bit below 60 Hz first before you begin to EQ elsewhere).
4. If you’re having trouble with the mix because it's sounding cloudy and muddy on the bottom end, turn the kick drum and bass off to determine what else might be in the way in the low end. You might not realize that there are some frequencies in the mix that aren't musically necessary. With piano or guitar, you're mainly looking for the mids and top end to cut through, while any low-end might be just getting in the way of the kick and bass, so it’s best to clear some of that out with a high-pass filter. When soloed the instrument might sound too thin, but with the rest of the mix the bass will sound so much better, and you won’t really be missing that low end from the other instruments. Now the mix will sound louder, clearer, and fuller. Be careful not to cut too much low end from the other instruments, as you might loose the warmth of the mix.
5. For dance music, be aware of kick drum to bass melody dissonance. The bass line is very important and needs to work very well with the kick drum when it’s reproduced over the huge sound systems commonly found in today's clubs. If your kick has a center frequency of an A note at around 50 or 60Hz and the bass line is tuned to A#, they’re going to clash. Tune your kick samples to the bass lines (or vice versa) where needed.
6. If you feel that you don't have enough bass or kick, boost the level, not the EQ. This is a mistake that everyone makes when they’re first getting their mixing chops together. Most bass drums and bass guitars have plenty of low end and don't need much more, so be sure that their level together and with the rest of the mix is correct before you go adding EQ. Even then, a little goes a long way."
You can read more from The Mixing Engineer's Handbook and my other books on the excerpt section of bobbyowsinski.com.