Side-chain Compression Using Waves RCompressor

In this tutorial I have taken the concepts discussed by Ilpo Kärkkäinen in his ‘Bassline Mojo’ article and expanded on the theory discussed to help create further balance between the kick and bass in the low end. I would highly recommend reading Ilpo’s excellent article first and listening to the audio examples provided to help better understand the theory discussed here. The DAW I’m using to demonstrate is Pro Tools, but the application of this theory and the use of Waves Renaissance Compressor in this fashion can be used in any other DAW such as Logic or Ableton Live.

To begin with, it would be a good idea to discuss what exactly side-chain compression is and how the RCompressor works.

What is Side-chain Compression?
Side-chain compression occurs when an input signal from another source has been selected as a trigger or key input for the compressor. This key input is the determining factor in how much gain reduction takes place on the output signal. There are many applications for this type of compression, such as overall volume ducking, EQ control (like a de-esser), side-chaining kick drum and bass guitar/bass synth etc. In this particular last example, its purpose is to aid in low end balance, along with emphasizing/preserving kick transients and headroom.

What does the Renaissance Compressor Do?
The following information is taken from the Waves Renaissance Compressor Manual and has been adapted slightly to explain its usefulness and industry standard effectiveness as a side-chain compressor.

Renaissance Compressor is a classic warm compressor and expander, with a simple, optimized interface. The Waves ARC (Auto Release Control) algorithm is capable of delivering significantly greater RMS levels (lower peak/RMS ratio) for heavier compression levels. This is particularly useful in the case of side-chain compression, because sometimes, such as in the dance world, you will want to hear pumping compression throughout the track. Classic 5- control setup is at the core of the interface, supplemented by a Release Mode button (ARC/Manual), plus the gentle Character control (Warm/Smooth), and the Behavior control (Opto/Electro).

The settings I've used in the example audio

The settings I’ve used in the example audio

Release Mode
This button selects between Auto Release (ARC) and Manual.

ARC mode uses the Waves auto-release technology. You set the release time as an overall scaling factor and ARC varies it from there depending on the input signal. In this case, our input key signal is coming from the kick drum, so the fact that the overall character of the RCompressor is similar to very responsive vintage program compressors works extremely well for this application.

Manual mode is fully manual, with no ARC (Auto Release Control). In my example, I’ve used ARC but in other situations, I will use the fully manual mode.

Compression Behavior
Electro (the original mode of the v1.0 software) has a release time behavior that is increasingly faster as the gain reduction approached zero, but only when gain reduction (GR) is less than 3dB. When GR is above 3dB, the release time becomes slower, behaving more like a leveler in high gain reduction situations. Therefore, when used with moderate compression, the Electro mode produces a great increase in RMS (average level), and is ideal for “loud” applications.

Opto is actually the inverse of Electro. Opto-coupled behavior always “put on the brakes” as the gain reduction approaced 0dB, i.e., the release time gets slower as the “needle comes back to zero”. As in Electro, this is true only when the GR is less than 3dB; when greater than 3dB, the release time is faster.

With the RCompressor’s two types of compression behavior explained, you can set it to either Electro or Opto depending upon how you would like the trigger (kick drum) to affect the music. I’ve used the Electro setting in this example as the gain reduction is between 6-12dB. That means that the release time of the RCompressor will be slower and will help to control the level of the bass a little more.

This button chooses between Smooth and Warm low frequency characteristics, which certainly can also affect wideband character, depending on the source material.

Warm adds low frequency harmonics as deeper compression is applied (greater gain reduction). Smooth avoids adding such harmonics, keeping the sound as close as possible to the original.

In using the RCompressor as a side-chain tool for low end, it makes sense to use the Smooth setting as you generally will not want to add extra low frequency harmonics to a situation that requires low end management already. However, there may be times that the use of the Warm setting is more appropriate as not many mixing “rules” can be completely set in stone.

Threshold is the input level above which the soft knee compression or expansion starts acting to a significant degree. The threshold slider is beside the Input Meters for easy adjustment.

For side-chain compression, it helps to drop the threshold slider down quite low to create the effect and almost exaggerate it, then adjust higher or lower to suit the material.

Note: the Renaissance Compressor uses a soft knee, so compression and expansion start with signals that are 3 dB lower than threshold.

Adjusts the compression or expansion ratio for signal above Threshold. The Renaissance Compressor ratio covers a wide range of compression ratios (1.01:1 to 50.0:1), as well as expansion ratios (0.99:1 to 0.50:1). The Ratio fader is beside the Gain meter.

In this track, I’ve used a 4:1 ratio.

The value is in milliseconds, from 0.5 to 5000 (5 seconds). It controls the response time of the onset of compression or expansion.

My attack time of 15.8ms is a relatively “medium” attack time. The attack time will depend on the song but I preferred this type of attack to control the level of the bass in this instance.

The value is in milliseconds and controls the release characteristic (linear when ARC is off). When ARC mode is engaged, the Release controls acts as an overall scaling factor around which the ARC technology works.

My release time is 33.4ms and is quite fast. I will often use a fast release time when I’m using a high amount of gain reduction (in this case 6-12dB) in a side-chain application, to create a slight pumping effect.

The value is in 0.1dB steps. Adjusts the output gain of the compressor, from +30.0 to -30.0 dB.

I’ve added 1.7dB of makeup gain to match the level of the bass when the RCompressor is bypassed.

How do I do it?
So with what the RCompressor does explained, how do I actually employ the technique?

As I am expanding on the theory involved in the ‘Bassline Mojo’ article, I have three separate bass tracks in my session. They all contain the same audio material but two tracks are duplicates of the original. These three tracks have been sent to a Stereo Aux called ‘All Bass’.

All Bass Aux

This auxiliary track can control the panning, automation and overall levels of the combined bass tracks, along with the ability to add further inserts that affect all three tracks if necessary.

On this auxiliary track, I have instantiated an RCompressor as an insert.

All Bass RCompressor

I have also selected ‘SIDECHAIN’ as the key input. I simply selected an available bus and renamed it ‘SIDECHAIN’.

I then duplicate my kick drum and do not monitor it. I remove the monitor output in Pro Tools and create a send from this track, sending the signal to ‘SIDECHAIN’ at 0.0 on the fader. I also put it in PFL so that it is always sending, even if the duplicated kick drum track has been muted.

Kick Send Duplicate

So, from my original explanation of side chain compression, the input signal is coming from the duplicated kick drum and has been selected as a trigger or key input for the RCompressor. This key input is the determining factor in how much gain reduction takes place on the output signal of the ‘ALL BASS’ track, thereby controlling the bass. If you wanted to just control the level of the low end of the bass, you could place the RCompressor insert only on the low bass track and there would be no gain reduction on the ‘Mid’ or ‘High’ bass tracks. For this track, I wanted the compression to affect all three tracks.

The kick and bass together without any side-chain compression would sound like this:

With side chain compression added, this is how they sound together:

With side-chain compression added, the kick is much more pronounced and rounder. Even though there has been no direct volume adjustment on the kick track itself, the level of the kick seems much louder. Rather than the bass and kick fighting each other for space, the kick is pronounced and the bass is supporting with effect.

This is the effect the side-chain has on the bass in solo:

Finally, here is the effect played within the track and all instruments playing:

If we took off the side-chain, the track would sound like this:

Notice that we lose quite a lot of the “Four on the floor” feel, the low end becomes a little boomy/unbalanced and we lose some of the clarity of the high-end/mid-range instruments.

There are many other applications for using the Waves Renaissance Compressor in a similar fashion, as earlier discussed. For example, you could use it to duck guitar parts when a vocal part needs to be the prominent element in a mix.

You could also side-chain some of the lead instruments or pads along with the bass, so that the kick cuts through all instrumental elements to create a “pumping” style or effect. Examples of tracks using similar techniques are in the chorus of ‘She Wolf’ by David Guetta and the intro to ‘Crew Love’ by Drake.

The more “standard” use of side chain compression to control the low end, as discussed in this article, can be heard in a multitude of tracks. Check out the chorus of ‘Part of Me’ by Katy Perry; for how it’s used to help create a big pop sound, ‘Awake’ by Tycho; in a more relaxed style on a bass guitar, and ‘Massage Situation’ by Flying Lotus; for a glitch hop application of a side-chain.

If you would like me to post a video on how I personally use the RCompressor to achieve this effect, then drop a comment below and I’ll get one up based on demand!

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