How to Hear Sidechaining

You’ve heard it said countless times: sidechaining is the key to achieving that all-important “perfect low end”. But how do you really judge what’s going on down at the bottom of the frequency range? Here are 7 things you can do to help make sure you’re assessing your ducking as it truly is.

1. Be clear on your sidechaining objective

Let’s start with the fundamentals. The reason you’re sidechaining your kick and bass is to maximise the punch and clarity of both parts by separating them, so that they don’t hit at the same time – but there’s a lot of variance and nuance in that central proposition.

If you don’t know how your sidechaining is supposed to sound, you have no hope of hearing and understanding what’s going on.

It’s always imperative, then, to be mindful of the precise sonic styling you’re looking to achieve, for which, broadly speaking, you have three options:

• Slow and pumping → The kind of overt sidechaining used as a compositional/arrangement feature, where the bassline is effectively ‘gated’ by the timing of the ducking, so that it hits on the offbeat.
• Fast and punchy → The bass ducks in and out quickly around the kick drum, so that the two are only slightly disconnected in time.
• “Invisible” → Ducking is applied transparently, so that the kick drum flows into the bass, and the volume modulation isn't obviously audible.

If you’re new to sidechaining, it’s well worth putting in the time to learn how all three of these styles sound and feel, so that you’re heading in the right general direction right from the jump.

2. Listen with headphones

Clearly, if you can’t properly hear what your low-frequency signals are doing, you’re never going to be able to manipulate them effectively, so monitoring is a key consideration in the successful application of sidechaining. Unless you’re working in an exceptionally well-treated studio space, on a set of high-end monitors with a subwoofer, you’re simply never going to hear those super low signals.

Assuming such exceptional facilities aren’t available to you, the solution is to supplement whatever speakers and space you do have with a quality set of headphones. By taking room acoustics out of the equation and providing low-frequency extension far deeper than your average monitor setup, a decent pair of cans will enable you to really zoom in on those lowest octaves and fully assess your kick/bass ducking.

Of course, when it comes to monitoring, headphones shouldn’t replace speakers – rather, they should serve as a complement to them, used specifically for close-up analysis of issues that speakers can’t convey.

So, in the case of sidechaining, use your monitors to get the ducking set up and sounding generally ‘good’, then switch to headphones to make sure you’re not missing anything untoward in the sub-bass. An overly steep or shallow ducking curve that could be improved using multiband processing, for example.

3. Illuminate low-end excess with a limiter

Given that the whole reason to duck the bass with sidechaining is to prevent the over-accumulation of low frequencies through the kick and bass coinciding, wouldn’t it be great if there was something we could use to clearly hear that over-accumulation when it happens? Well, wouldn’t you just know it, there is: any limiter plugin!

With the Mix parameter in your ducking plugin set to 100% dry, place a limiter on the master output, or the group bus to which your kick and bass are routed, and raise the input until you can hear it start to distort unpleasantly. With the signal pushed hard into the limiter ceiling, the mushiness and lack of definition of the unducked kick/bass combo will become readily apparent, making its subsequent correction as you gradually dial in your sidechaining (by raising the Mix control and adjusting the modulation curve) easy to hear.

To be clear, the distortion you want to get rid of is the nasty intermodulation distortion that affects the kick and bass collectively, as a single entity. The distortion that occurs with each element individually doesn't necessarily need to be resolved, as long as it doesn't obscure their fundamental notes.

Finally, don't forget to remove or disable the limiter once you've got your ducking set up!

4. Solo the kick and bass – but not too often

It should go without saying that soloing the kick and bass (either individually or on a shared group channel) is a very good way to hear the action of your sidechain ducking, so don’t be shy about doing so. Monitoring your kick/bass combo in isolation enables you to very precisely shape the ducking curve, shift your multiband crossovers and adjust the dry/wet mix, with nothing else obstructing your “view”, so to speak.

However, as is the case with any part in any mix, soloing should only be done infrequently. Ultimately, the tracks being soloed won’t ever actually be heard on their own, and you don’t want to give yourself a misleading impression of how they sound in situ. Think of it as a way to zoom in on your sidechaining temporarily to check and hone it, before zooming back out to get back to the bigger, more meaningful picture.

5. Mute other tracks

Following on from that, if you find that your kick and bass sound great when soloed but not so good when dropped back into the full mix, there are two possibilities.

The first is that you’ve over-tweaked the ducking in solo, in which case, have another go at it in the context of the full mix.

The second possibility is that some other element is interfering with the kick and/or bass, causing an issue that’s only apparent when they’re all heard together. If that’s the case, mute the other tracks one by one until the anomaly disappears, thereby revealing the source of the problem, which can then be addressed as necessary.

6. Use visual aids

Another great way to get a handle on what’s happening with your sidechaining ‘down there’ is to use visual referencing. Monitoring your kick and bass with a spectrogram and/or oscilloscope can be particularly helpful if you don’t have a subwoofer, as it lets you at least see the very low frequencies that your monitors can’t reproduce (below around 50-60Hz).

Even if your studio setup is blessed with a sub, visual monitoring provides an alternative source of insight into the specifics of sidechaining that can really aid in your overall perception of it.

Kickstart and VolumeShaper are both well equipped for visual monitoring. With either plugin loaded onto your bass channel, and your kick drum routed into the sidechain input, you’ll see the audio waveforms for both parts together in the Oscilloscope: the kick in yellow, the bass in grey (Kickstart) or pale yellow (VolumeShaper). To see the summed kick and bass signal, you can then follow that up with ShaperBox’s Oscilloscope Tool on the master bus.

7. Use a low-pass filter

Our final isolation technique for sidechain assessment is to insert a low-pass filter on the master output of the mixer with the cutoff frequency set to around 100-150Hz. This effectively ‘solos’ the low end of the mix, which will make it much easier to hear your kick/bass ducking than with everything in.

The difference between such filtering and soloing the kick and bass, as suggested above, is that filtering enables you to hear how much of the other instrumentation is reaching down into the low-frequency range as well. Ideally, that will be very little or none – so when you mute the kick and bass with the low-pass filter active, you shouldn’t hear much of anything else. If you do, consider high-pass filtering or otherwise tweaking the interloping parts to lift them above 100Hz, as you want mostly kick and bass below this point.

In this example, you can hear:

1. Four bars of a full mix with Kickstart ducking the bassline

2. Four bars of the same mix with a 130Hz low-pass filter applied

3. Four bars with the low-pass filter applied and Kickstart bypassed

Note how clearly the difference between the ducked and unducked bassline can be heard with everything else filtered out.