Low end theory: EQing kicks and bass
Ever wondered why your favourite producers’ kicks and basslines sound so gratifying? RA’s Jono Buchanan boldly crosses the low frequency minefield to tell you why.
To understand bass we need to understand a little bit about harmonic content and about the physical make-up of a speaker too, whether it be a studio monitor or a monstrous club system. First of all, low-frequency waveforms contain tons of energy—just look at the density of a bass part or kick drum as a waveform and you’ll see what we mean. This is in part because most kick and bass sounds are rich in harmonics. In addition to a loud fundamental bass frequency, there’s lots of other content present in the sound. So if you use an EQ plug-in on a kick drum and start messing around with low mid-range, upper mid-range and even the treble content, you’ll hear substantial changes in timbre.
Here’s the first easy mistake to make: assuming that bass drums and bass parts only contain bass frequencies. As you can hear from the EQ’d kick drum sample, which automates a sweeping notched EQ from 50Hz up to 5kHz and back down again, nothing could be further from the truth—you can hear just how many frequencies are active. With this information, we can deduce that bass content has the potential to run riot over many frequencies of our mixes, unless we’re careful about the sound choices we make, the treatments we use parts we program. So, why is it also helpful to understand how a speaker works? Well, strange as it might sound, it’s extremely easy to forget that a speaker cone is a moving, physical object and that as it moves, the content of your mix moves, too.
The average lowest frequency people can hear is about 20Hz but club systems are capable of responding to much lower frequency content. Bass parts also contain harmonics below the fundamental frequency as well as those above. So it’s likely that lots is happening in your bass parts below what you can accurately monitor on your system at home. This content has the potential to wreck your mix in a club and here’s why. Completely hypothetically, let’s suppose your mix contains a loud frequency cycling at 1Hz; at one cycle per second, in other words. That means that every second, the speaker cone, if it could produce this frequency, would vibrate from front to back.
Let’s suppose this super-low drone plays underneath a kick drum playing a four-to-the-floor pattern at 120 BPM. The result would be that the speaker cone would move to the back for the first and third kicks and to the front for the second and fourth. The important point is that the drone, despite being below an audible frequency threshold, would still be impacting physically upon the speaker. This in turn means that the sound of your kicks would be seriously compromised—two of the four would be too punchy and two would be dull and muted. This is a hypothetical and exaggerated example and yet it’s completely true that your mixes could suffer from a milder version of the same problem; if there’s thumping bass in the sounds you choose below the frequencies you can hear or more likely monitor through the speakers in your studio, you could be in trouble when your mixes translate to a club.
However, if you’re now thinking that brutally EQing all of the sub-bass out of your kick and bass parts will provide a solution, it might not be quite that simple. By doing this, you’ll lose a lot of the energy on which well mixed club records rely, so it’s important to be a bit smarter than that. Instead, we’re going to turn our attention to how to get kicks and basslines integrating well and we can immediately put our theories about both harmonic content physical nature of a speaker to the test.
Here’s a simple first test; program a four-to-the-floor kick at somewhere between 120 and 130bpm—any kick will do but definitely choose something with some thump in it. Then program a bass pattern (again with a nice rich bass sound) to go over the top with some bass notes coinciding with the kick and others falling in the gaps between kick hits. Just a bar will do, but you can make a longer pattern if you like.
Turn the mix up loud, loop your pattern and listen carefully to the mix. What do you notice about individual bass notes and kicks when they fall separately from one another, compared to those which coincide? What you should hear is that those two sounds appear full and rich when separated. But when they land together, the sound is smaller, more contained and, in extreme cases, almost slightly phasing. You should now know why: the speakers are sharing this overload of bass information when two strong bass frequencies force it to move at the same time, whenever notes strike together.
Now it’s time for something radical. Put a low pass filter set to 180Hz on the kick drum with the most brutal slope your EQ can provide—preferably something like 36 or 48dB per octave. Now, put a similarly harsh high pass filter on the bass sound and set the frequency threshold at 180Hz again, so that this time you’re scooping out tons of bass. Press play again to hear our example.
You should find that while both sounds are massively compromised, your speakers are likely to be much happier. The kick is providing the thump, while the bass is much thinner, sitting atop the kick without compromising the overall mix. The musical integrity of the part is compromised to a fault, but the good news is that we have found a solution to stop the bottom end of our mix becoming too full and overloaded. Now let’s find one which doesn’t kill the music.
What we should take from our filtering test is that removing frequency content to make room for another sound is an effective solution. Those records you most admire thumping out of club systems have got producers behind them who know that the key to bass integration is to decide exactly what the role is for the bass elements of a track and how to prioritise frequencies in one sound over frequencies from another.
In other words, if you want the kick drum to provide a sound that will rattle your rib cage, it might be a good move to duck that frequency from the bass part so that the kick can really take over at that point. Equally, if you’re using a fat, rich bass sound, it might be a good idea to warm up the low mid-range and similarly duck the kick here to allow the bass to strut its stuff.
Let’s go back to our kick and bass pattern from the previous example. Here, we’ve got a rounded kick drum which we want to get thumping harder, so the first job is to find the frequency within it we want to use to get the kick banging. The best thing here is to use your ears—fire up the EQ, narrow a frequency band and boost frequencies somewhere between 80Hz and 200Hz.
Depending on the kick you’ve used, you should find your kick lights up somewhere within this range. If you want to use your eyes as well as ears, you can cheat slightly by placing a frequency analyser before the EQ to evaluate the specific frequencies of the kick drum. Once you’ve found a frequency you like, boost it a little (by no more than 3-4dB) to give the sound extra bite.
Open another EQ plug-in on your bass sound. Narrow a band around the same frequency and drop the volume by the same amount. What you should find is that the hole created in the bass is nicely filled by the kick and that your speakers are responding well—the kick should sound clearer, while the bass won’t be too compromised. Again, check ours.
Next, look for a frequency within the bass you want to boost to enhance it. Unless you’re using a sub-bass, this is likely to be a higher frequency than the one you chose for your kick, so bring out a little of the lower or upper mids until your bass sounds rich and full.
Having identified and boosted the frequency again, return to your kick drum and scoop this frequency out of the kick, even if you think that the kick isn’t having a great deal of effect at this point (you might well be surprised). The result should be clearer still—the kick has a clear identity as the foundation of your track, while the bass now has room to breathe and emphasised higher frequencies.
Lastly, experiment with using a filter to slope away the low frequency content from the bass. Don’t be as extreme as we were in the previous example—a 12dB per octave high-pass filter will be plenty—but try rolling off from 50Hz downwards. Again, you should find the mix benefits from enhanced clarity. You can hear ours.
Everything we’ve looked at so far has implications for the use of effects at the bottom end, too. Plenty of producers like to enhance their bass sounds with delays and/or reverbs. While there’s no reason to shy away from using effects on bass-heavy sounds, bear in mind that if there’s lots of bass present in the effects, the speakers will again struggle to do your mix justice.
The easiest way to avoid this is to either turn to the EQ functions within your chosen reverb or delay plug-in, or to employ a dedicated EQ after the effect to ensure that only the frequencies you want are escaping from your effect treatments. Delays in particular are a problem as they effectively create more notes in your pattern. If you let all frequencies into and out of your delay plug-in, particularly if you’re using high feedback levels, you’ll soon find that the bass end is overloading.
As a start, try restricting the delay content to ensure that nothing gets through below 300Hz. If your bass sound is busy in the upper mid-range, it’s also a good idea to cap the top frequency content so that the bass doesn’t encroach on higher frequency sounds in the mix. Ours only lets through frequencies between 320Hz and 2.9kHz.
Here we have a plate reverb on the bass with no EQ applied, which muddies the lower frequencies.
With a simple high pass, we now have a cleaner reverb that subtly accentuates the mid-range.
As ever, the proof is in the listening. But if you start to take control of the EQ in the bass end of your mixes, the benefits should be apparent when you hear your studio mixes in a club. It’s also worth bearing in mind that, in terms of testing and mixing your tracks, bigger monitors tend to more accurately reproduce bass. Invest in the best system you can, or try to gain access to a system where you can test your mixes.
It goes without saying that you’ll struggle to accurately pin down the bottom end if you’re mixing on headphones as many of the frequencies discussed simply won’t be heard, even on more expensive models. Remember, most importantly, though, that EQ can be used to cut as well as boost—and a little of both on your kicks and bass parts could make all the difference.