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Every mix engineer at some point will question whether the bass (low-end) of the mix will have the emotional impact desired, meanwhile not cause ill-effects in mastering, such as a "pumping" effect. EDM seems to be one of the few genres of music where the pumping effects of the bass drum (or 808) is actually desirable.
The truth is, next to capturing a great performance, the mix is the first real production the artist gets to hear as an ensemble. This is where production takes a center stage. The vocals and instruments must be negotiated throughout and decisions are to be made that will affect the outcome listeners will enjoy. Are the rhythm guitars loud enough? Or do they swallow the lead vocal? During the verse, do these guitars need to be pulled back to allow the subtle emotion in the vocal to be the most prominent statement?
The hardest instruments to negotiate into the mix are the bass guitar and kick drum. These, not only sit beneath the mix, they routinely play a supporting role, where the musicians aren't always happy they've been turned down. Generally, they aren't the center point of the song's message. They also are not the instrument a listener necessarily wants to hear in front of everything for the entire mix. That would grow old, fast. Imagine your best friend pounding his fist into the center of your back in rhythm with the kick drum every time you listened to a certain song. It would be cool at first, but you're likely to grow weary and fatigued from that repetitive impact.
Nevertheless, in many genres and songs, even though they aren't the star of the performance, the bass and kick instruments are so crucial to the emotion of a song. If they barely exist, the song still can convey some emotion, but without that "bottom-end" flourishing, listeners might not find the production as compelling. Yes, I know an acoustic ballad doesn't count as much, but a great rock record would. Hip-Hop, even more. EDM, you bet!
So, what does it mean to have powerful, impactful bass in a mix? It means, when you turn up the mix in your monitors, you can actually feel the impact and relish the emotional fundamental frequencies of the bass guitar or synth. If it fills out the bottom end of the audio spectrum, well done! If they're indistinct, muddy, cluttered, you'll have a mess when it comes to mastering.
"Unlearn what you have learned"
We've been taught in mix classes to host a the resonant and booming frequency of the kick drum either above or below the fundamental frequencies of the bass. This gets them out of the way of each other power and sonic character. The kick drum can be boosted below the bass, or the bass can be boosted below the kick. So long as they're not both taking command of the same fundamental frequencies, such as 60Hz, for example, you're fine. They'll both be heard, distinct, and allow your bottom end to be easily understood.
Ehh, well, I have an issue with this. What if the bass and the kick benefit from the same booming frequencies? I find this to be the case more often. I believe a strong foundation in the bottom end, especially the sub-low frequencies between 25-45Hz is absolutely crucial! If the kick drum is booming down into the 30Hz range, but the bass is thin and brittle, that may sound terrible and disconnected. That's like hosting Stanley Clarke's jazz bass to lock in with John Bonham's kick drum. It just doesn't work.
A good cohesive balance of frequencies is a must and I believe they should form a bond. They don't need to be separated so much. They can both play in the same frequency range. However, we've also been told in mixing that we can make use of the side-chain input of bass compression, triggered by the kick drum. Clever! Yes, I'd recommend trying that.
It's in the faders
A great mix is 85% in the levels and panning. In fact, if a band is recorded very well, by an engineer who essentially mixes with mics, positioning, room, and incoming levels, the mix will require far less resource hours to finish. Fortunately, it's also the place most often overlooked. For example, Grammy winning mix engineers such as Chris Lord Alge and Michael Brauer are more likely to bring up faders and get them all close to a finished position as possible before touching a single EQ or compressor knob. They want to know what needs to be fixed first. This is why I address levels first in the bass/kick realm.
For bass, it's best it isn't made prominent in the mix unless you're Geddy Lee and you command your bass be heard at all costs (heh). Bass should never overshadow the kick drum in the bottom end, where at times the kick is mixed at a lower level than the plucking impact of a bass string. The kick drum needs to be brought up. Even if it's questionable as to whether it might be too loud or booming. If it doesn't exhibit nasty reverberation or decay issues, it can be tamed, even in mastering. Often I hear mixes where the kick drum is simply too quiet and timid. When I listen on my speakers and my planar headphones, I know well within 2 beats if the kick drum is too low in the mix.
The bottom end is crucial that levels are balanced nicely. The lack of low-end can quickly ruin an otherwise stellar mix--yes, even knowing the bass and kick are not to be the center of attention. Some forget that the rhythm section between these two actually help hide non-quantized or even sloppy guitars. Because the bass and kick are tight, the other parts can actually feel tighter.
It's in the EQ
You'd be amazed at how cutting some mud out of your kick drum can allow it to be heard, meanwhile not trample all over everything else. Cutting between 120-400Hz, and boosting around 60-77Hz is amazing! Also boosting (in more rocking mixes) between 3-6kHz can also do some incredible things to the kick drum's impact. However, cutting out the super low end on a kick drum using a High-Pass-filter or Low-shelf is largely what you need to tighten the kick drum and keep it from overwhelming the rest of the mix. Just be sure to bring up the level of the kick to be heard again.
Boosting the low end with a Pultec-style EQ is divine. This EQ is a rather cryptic tool, but it is one I'll often use for boosting low-end. It's certainly an EQ where it's better that you cannot see the curve. You must use your ears. I like that.
To start, I'll set the Low Frequency to 20 or 30 CPS, then I'll set the Bandwidth to 1 or 1.5. Finally, I'll begin boosting the low-end to roughly 2 or 3 to hear the effect. Finally, I'll back off the Gain to ensure I'm not clipping.
It's in the compression
There's no shortage of great compressors in the realm of plug-ins and hardware. However, there's no shortage of compression mistakes made because of that. I won't waste time going through all compression types and why or why not use them, but I will make some recommendations.
First, when it comes to a drum buss, or a mix buss, VCA compressors are "da bomb"! This type of compressor can add punch to a mix without ruining it's transients, or causing ill pumping effects as bad as others. For full-frequency compression, VCA compressors are wonderful!
This one below is my absolute favorite!
The Waves SSL 4000 G is a true game-changer. There's several emulations of this plug-in, and they're all just fine. When using this plugin anywhere, I start with a threshold of +15, Attack at 30ms, Release at .1s, and ratio of 2:1. As my music is playing, I'll bypass the plugin and set the Make-up so that whether the plugin is active or not, the level doesn't change.
Next, I'll start moving the threshold until the needle moves no more than 2dB. From there, I'll adjust so that the kick drum has a bigger impact, but without negatively affecting the rest of the music. This compressor is profound for not causing pumping effects when I don't want them, meanwhile making the kick drum more punchy.
You can try other VCA compressors as well. Some work really well. One called the "Town-House" is quite fun! Some hardware units also can't be denied.
Another VCA I favor is the Vertigo VSC-2.
It isn't just another great-sounding VCA compressor. It has some hidden features I find quite useful, such as the SC (Side-Chain) filter, in case I want a VCA compressor to use mostly for snare drum work on a drum or mix buss. It can also provide an M/S compression if you have an M/S encoder/decoder plugin to place before and after, as it can operate in dual-mono mode.
In Mastering
Generally, the bottom end of the mix is one area I pay extra close attention to. Whether you may deem the bass or kick drum crucial instruments in the mix, they play a massive role in the sonic performance of the mix. In the master, this can make a difference between an amateur and professional, commercially successful master.
When I receive a mix in which I find the kick drum lacking, or the bass guitar is a bit much, I'm likely to employ a dynamic EQ. DMG Audio Multiplicity is my favorite right now, having replaced an older, neglected Flux Alchemist. I often find myself trying to heal a weak kick drum in a mix without negatively affecting anything else.
Multiplicity offers an insane amount of tweak-ability and problem-solving. If I need to adjust the fundamental frequency or level of the kick drum, this is a tool I often use. The Fabfilter Q3 has a great dynamic EQ, as does Waves (F6), but I find Multiplicity to be more of a tool to fix problems rather than an easy way to monkey around with dynamics of an EQ frequency.
The Good News!
If you're uncertain whether your low-end is sufficient enough or balanced well to play a part in a powerful master, feel free to contact me and I will give your mix a listen. I'll usually offer some EQ or compression tips to help you find the right levels, EQ, compression, and impact.
Also, don't forget that, when you contact me, you'll receive a free e-Book that's loaded with tips to help you get the most from mastering. Until then, don't fear the low-end! Take Care!