How to Sub: All the basics of dancefloor sub


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Let’s Get Deep! Using Sub Bass in Music Production

Sub bass these days is one of the most essential aspects to a dance music track – and now that we have decent sound systems and quality rigs in clubs, it’s ever more important to get it right. But what’s the best way to do it? And what makes a good sub anyway?

We all know what sub-bass is – it’s that bedrock of your track, ranging in the 40 – 100 Hz region; either underpinning your bassline or kick (or both). But there are plenty of misconceptions about it, and how you should treat it, so lets clear a few of these up now.
First, a simple sub-bass is a sine wave. That’s all. It makes things nice and easy, because there’s no need to worry about what would be a good synth to use for sub bass; just load up a sampler with no patch, and use a sine from that. Done! We could go into the maths of it, but essentially any other type of wave (lets say a square wave) – has higher frequency harmonics in it; on a square wave these appear to be the ‘corners’ of the square. Low pass filter a square wave and you’ll be left with a sine again. If people talk about a ‘fat’ sub, then it’s probably because there are higher frequencies in the sound. You might want some of these harmonics though – we’ll touch on that shortly.
Because sub bass is such an ‘extreme’ frequency, there are plenty of technical issues that come into play. A lot of them arise from the limitations of vinyl or club systems. You need to remember that as frequencies get lower, the wavelength gets longer; this means a speaker (or needle) has to move twice as far to create the sound, and will need much more power to push all that air. As such, it’s a good idea to try and keep your lowest frequencies above about 40Hz, which is around the notes of E1 or F1. Below this, at the kind of volumes dance music requires, it starts getting increasingly difficult to cut to vinyl (the grooves need to be further apart, limiting the length of the track) – and not all club systems can handle the extreme lows anyway. Your author has first hand experience of playing one of his own tracks in a busy club, and finding that it sounded like there was no sub-bass on the track whatsoever. The sub (on the note of D1) was too low for the club system to handle; it sounded terrible!
Another issue you’ll see discussed is that of panning. The accepted wisdom is that you need to have your basses in mono, and this is a sensible option to go for. Vinyl can skip and jump if the deep bass grooves are significantly off to one side; and anyway sub-bass frequencies are below the level that you can reliably tell where they’re coming from (the wavelength is longer than the width of your head, for a start). A mastering engineer or vinyl cutter may well decide to mono a mix anyway below around 300Hz if there are any problems with stereo bass – so you’ll need to make sure (as always) that your mix sounds good in mono too. And again there can be club problems – many club soundsystems are mono anyway, but even if not, a sub panned hard will only be coming from one set of bass speakers. And that’s going to sound weak.
Besides the technical, engineering aspects, you also need to write your subline sympathetically to the rest of your track. This means, for a start, have it monophonic – clashing notes will sound muddy and use up headroom. So make sure the ‘release’ on your ADSR envelope is tight, to ensure that notes don’t overlap. If you’re using a subby kick, then try to make sure that your sub isn’t playing at the same time – or if it must, sidechain it off the kick to duck the volume, again for headroom purposes.
To return to the subject of harmonics, this is something that can be useful for a number of reasons. You can add a sense of warmth, or ‘fatness’ by adding in frequencies above the standard sub region – we’re talking 150 to 400Hz here – that will give things more of a glow. But, arguably more importantly, they’ll help the sub come through on smaller speakers. A radio or an iPod dock will struggle to reproduce frequencies right at the bottom end; not so much of an issue if the top end of your bass is a raging wobble dubstep affair, but if you’re writing more of a roller, then it may sounds like there is no bass at all. Get some higher frequencies on your sub and people will be able to hear what it’s doing, even if they can’t feel the weight. A simple way of doing this is to set up a send to a buss, and then distort it and bandpass filter it around 200 or 300 Hz. This way it will copy the original sound, shouldn’t interfere with the low end (as you’ve high passed it) and will give extra interest for the listener.
Sub-bass is a tricky subject, and it’s something that requires practise to get right. But learn the basics and you’re halfway there. So, jump straight in – fire up your speakers and get writing those big basslines!
Thanks for the useful post.

Production-wise it's basic stuff of course. What got me thinking was the thing about the wavelength of the sub bass though. "For a start, it's longer than the width of your head." After some quick maths I have calculated that notes up into the 6th octave or so have wavelengths longer than the width of my head (lookup table). Does anyone have the actual explanation why we can't perceive stereo below 200 Hz (a number commonly mentioned in production forums) ? :)