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, which means that as well as a loud 'fundamental' bass frequency, there's lots of other content present in the sound, which means that 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.
The average lowest frequency people can hear is about 20Hz but club systems, in particular, are capable of responding to much lower frequency content than that and as bass parts contain harmonics below the fundamental frequency as well those above, 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 and 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 and the 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, though do create a longer pattern if you like.
Now, you should find that whilst both sounds are massively compromised, your speakers are likely to be much happier. The kick is providing the thump, whilst the bass is much thinner and sitting atop the kick without compromising the overall mix in the same way as before. 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 which 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.
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 and whilst there's no reason to shy away from using effects on bass-heavy sounds, do 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 and 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 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 become apparent as your studio mixes transfer to 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.