Sometimes it is desirable to hear the sound of a quality compressor making a drum kit pump. However, often a bigger, more even sound can be achieved by processing the side-chain of a compressor with an EQ. By doing this the compressor becomes much more versatile and the way it reduces the gain of the signal can be controlled. This is known as frequency conscious compression and many other effects are possible with this technique.
Every compressor has a side-chain circuit even though the user is often not aware of it. The side-chain generates a control signal that dictates, in conjunction with the compressor controls, how the gain reduction circuit behaves. Often the side-chain signal is identical to the input signal. The information used to control the gain reduction, is identical to the audio input to the compressor.
Low frequency sounds such as a kick drum have much more energy than high frequency sounds such as cymbals. This results in the low frequency elements of a signal dictating the behavior of the compressor and can result in the level of the signal being dragged down when a low frequencies are present.
When the Duende Channel is first loaded, it’s compressor is of the traditional type where the side-chain signal is identical to the input signal. Due to the flexibility of the Duende Channel, the compressor behavior can be altered quite considerably by assigning either the filter, EQ or both to the dynamics side-chain.
This can be done easily on the Channel by depressing the DYN S/C buttons found in both the Filter section and the EQ section. Depressing this will move the respective section into the side-chain circuit and remove it from the audio circuit. This means that if you have an EQ setting dialed in, and the DYN S/C button is subsequently depressed the EQ will no longer process the audio signal, but will become a control signal that is not present at the audio output.
To listen to the side-chain signal, press the S/C LISTEN button found in the OUTPUT section. This enables you to audition exactly what signal is controlling the dynamics. When any section is assigned to the side-chain, the Process Order graphic will reflect this to let you know how the routing of the channel is configured.
Process order graphic showing EQ and Filter assigned to Dynamics side-chain
No side-chain processing
Solo track 1 of tutorial 4, and you can hear the kick drum causing the hi-hat to reduce in volume when large amounts of compression are used. The snare drum has an influence too but to a lesser extent because it contains less low frequency energy. The hi-hat can be heard jumping up in between kick and snare hits, because as there is very little energy present in the side-chain at these moments the gain reduction is minimal.
High pass filtered side-chain
Solo track 2
Here the filter section is routed to the side-chain, and the hi-pass filter is moved to 500Hz to reduce the influence of the kick drum on the gain reduction circuit. Pressing the S/C LISTEN button enables you to hear this.
The sound of the drum kit is now more open, and the kick is let through more as the compressor acts less on these hits.
EQ and Filters to side-chain
Track 3 takes this a step further.
Firstly the EQ is turned on and assigned to the side-chain. Then a large EQ cut at 700Hz is dialed in which reduces the snare frequencies from the side-chain signal. Again, depressing the S/C LISTEN button will let you hear that the presence of the snare drum in the side-chain is considerably less. The kick drum is also reduced more as it has some energy in the 700Hz area.
The drum kit now has a more open, even sound where the kick and snare drum don’t kill the rest of the kit and it’s ambiance. Note that the output level is roughly the same as it was when nothing was assigned to the side-chain, yet the perceived loudness of the kit is considerably more.
This technique can be used on any signal where you wish to change how the compressor reacts to various frequencies that are presented to it. By assigning the EQ or filters to the dynamics side-chain, they are of course assigned to side-chain of the expander/gate, allowing frequency conscious gating and expansion to be carried out.