As the foundation of most modern music, the kick drum and bass guitar have a crucial role to play. While the foot and fingers are the most important factors in a grooving low end, there are steps the sound engineer can take to improve how well the kick and bass work together.
The goal is to have a kick and bass guitar sound that complement each other, not compete. When the drummer and bass player are working together, the bass becomes the pitched "extension" of the kick drum's attack. If the kick lacks clarity, or the bass guitar lacks fullness, this synergy is lost.
No amount of processing will make an unhealthy kick drum sound stellar.
Step one is to get the kick drum and bass guitar to sound their best individually. This is usually an easier task for the bass. It should be full but not muddy, clear but not thin. Most electric basses and amps will give you a clean direct sound that's 90% of the way there. Adding some EQ and filtering (more on these later) will usually do the trick.
The kick should have a strong fundamental thump sitting underneath a crisp beater snap. This can be a challenge, thanks to all of the variables that go into a kick drum sound: tuning, heads, damping, beater material, mic selection, mic placement, and more. Consider hiring a drum tech for your kit if the instrument itself is not sounding its best. In most cases, no amount of processing will make an unhealthy kick drum sound stellar.
Once you've got good signals flowing into your mixer, EQ and filtering become your main tools. When applying EQ, it may be helpful to think of the kick and bass guitar in three frequency ranges. The lowest is the fundamental (under 100 Hz), where your subwoofers are working and the sound is felt as much as heard. Next up is the mid bass (around 250 Hz), where too much energy can make both kick and bass guitar sound "boxy." Frequencies above 1 kHz are where the kick and bass guitar get their definition and clarity.
Though a kick drum emits a fundamental pitch (a sine wave), it shouldn't ring long enough to give the ear the impression of a note.
If either kick or bass guitar lack bottom end, increase frequencies below 100 Hz with a broad peak or bell filter (a shelf works, as well). If the sound is too tubby and indistinct, try reducing those frequencies. If the sound is clouded with too much mid-bass, use a notch to reduce those frequencies. Finally, use a broad peak or shelving filter for frequencies above 1 kHz. Frequencies around 1 kHz can add "growl" and "bite" to the bass guitar, while the 2-5 kHz range is usually more effective for bringing out the kick's beater attack.
Though a kick drum emits a fundamental pitch (a sine wave), it shouldn't ring long enough to give the ear the impression of a note. If a kick establishes a sustained note, it will clash with the bass guitar and other low-frequency instruments. Use muffling on or inside the drum to shorten the sustain. If that's not possible, use a gate on the kick. Set the attack and hold times to their shortest values (usually 0 ms), and the release time to around 5 ms. Increase the release time until you feel the deep fundamental from the kick but the sustain is eliminated.
Too much of a good thing (low bass) is a bad thing, especially in a typical sanctuary suffering from inadequate acoustic treatment.
Step two is to get the kick and bass guitar sounding their best as a team. Work with the EQ until the instruments are complementing each other in all three frequency ranges. Corrective EQ usually involves reducing one or more of these ranges to allow the other instrument to shine. For example, that problematic mid-bass around 250 Hz will usually require more attention when the kick and bass guitar are combined. Deep cuts in this range are often required to keep the two instruments working well with each other and the rest of the mix. Sound tip: use solo briefly to make an instrument sound its best alone (up in step one), but then make all subsequent adjustments in context.
The high-pass filter (HPF) is your next best friend for getting the kick and bass guitar working together. A HPF eliminates low frequencies, which may seem at odds with the role of the kick and bass guitar. In reality, both often generate more very low frequencies than the mix (or the room) needs. Sometimes it's beneficial to let one of the instruments speak more loudly in the lowest octaves and reduce deep bass from the other. If the mix is working with deep, loose low-end from the bass guitar, placing a 12 or 18 dB/octave HPF on the kick and bringing it up to around 80 Hz may clarify the low end. In other cases, your mix may clean up nicely if you let the kick's fundamental fill the lowest octaves as you raise the bass guitar's HPF into the 100 Hz range. Too much of a good thing (low bass) is a bad thing, especially in a typical sanctuary suffering from inadequate acoustic treatment.
Step three is to optimize the levels of the kick and bass guitar. It's often helpful to think of the bass guitar as an extension of the kick drum. The attack of the kick should flow evenly into the bass guitar's note as if they were one instrument. Some engineers like to set the bass guitar level for the mix first, then bring the kick up until it adds a strong (but not overwhelming) attack to the front of the note. Balance the snare with the kick and bass guitar, and your rhythm section will truly be a firm foundation.
