Dynamic Processing
Dynamic processing is “the control of dynamics either manually, or with automated devices such as gates and compressors.” This page covers how compressors and gates work and their parameters. Side-chaining is also covered.
Contents
Specification 👇
Component 1 Specification
Component 2 Specification
Component 3 Specification
Component 4 Specification
Compression
The first dynamic processing method is compression. Compression is “a process for controlling the dynamic range of a sound. It reduces the volume of the peaks of sound above a threshold by a predetermined ratio.”
In simpler terms, it narrows the dynamic range. It takes the peaks of a sound that are louder than the set threshold (in dB), and reduces them in volume by a certain ratio.
The diagram above on the left depicts an unaffected waveform with a varied amplitude. In the diagram on the right, a compressor has been engaged. The signals that exceed the threshold (black line) have been compressed and the new signal is shown in red. As you can see, it doesn’t necessarily compress the signal below the threshold – the amount that the signal is compressed by is determined by the ratio.
To the right is a compression graph. The graph shows the effect that a compressor has on a signal. When the compressor is engaged (when the signal level reaches the threshold), the output level is reduced by a certain ratio.
The ∞:1 ratio completely cuts any signal that goes above the threshold. Applying this harsh a ratio is known as limiting. A limiter can come as its own dynamic processor, and is defined by Edexcel as “a process for controlling the dynamic range of sound. It prevents the peaks of sound going above a predefined threshold."
If you want to know more about the difference between compressors and limiters, give this article a read.
Compression parameters
Gain input: the amount of signal being sent to the input stage of the compressor.
Soft/hard knee: a soft knee creates a more gradual change in volume. A hard knee is more abrupt/sudden.
Threshold: the point at which the signal is compressed. If the threshold was -15dB, the signal below that level would go unaffected. However, any signal that exceeds that level would be compressed.
Example of a Compression Plugin
Ratio: the degree to which the affected signal is compressed. The higher the ratio number, the more compression that’s applied to the affected signal, ie. a 6:1 ratio will compress the signal more than a 2:1 ratio. For an example, imagine you’ve set the ratio to 3:1. This means that for every 3dB that your signal goes above the threshold, only 1dB will be allowed to pass. So if your signal went 6dB above the threshold, only 2dB will be allowed to pass. If the signal went 9dB above the threshold, only 3dB would be allowed to pass, and so on…
Attack: this refers to how quickly the compressor responds to the signal. Measured in milliseconds. Too short of an attack (quick response) and you may lose the start of a sound, eg. the attack of a percussion sound, but too long (slow response) and the compressor might not react in time.
Release: also measured in milliseconds, this is how quickly or slowly the compressor is disengaged when the signal goes back down below the threshold. If its set too fast, the dynamics change too quickly, causing a pumping sound. Too slow and some quieter sounds might be compressed unnecessarily.
Output/makeup gain: due to the fact that you’re lowering the volume of all the louder parts of the signal and leaving the quieter parts, the overall signal will reduce in volume. You may need to boost the output level for the signal to remain audible within the mix.
Reasons to use a compressor
The main reason to use a compressor is to narrow the dynamic range of the signal. If, for instance, you had a vocal recording that had a large dynamic range, it would be difficult to set an appropriate level for the signal as it would jump in and out of the mix. If the signal is compressed, however, the amplitude of the signal is more consistent and therefore it will be easier to set an appropriate level for the track in the mix.
A compressor can also be used a deEsser, or rather compression is used in DeEssers. DeEssing is “the process of removing overly emphasised sibilant sounds (including ‘s’ and ‘sh’ sounds) by applying a dynamics processor to certain frequencies.”
You can also use compressors for creative purposes. You may apply the compressor to a drum sound and set the a high attack time so that it takes longer for the compressor to be engaged. This will result in a ‘punchier’ drum sound as the transient part of the sound will go unaffected but the ‘tail’ of the sound will be compressed.
Another creative use can be to create a ‘pumping‘ effect. As mentioned above, setting the release settings too fast, making the compressor disengage too quickly after the signal level has returned to a level below the threshold, can cause a ‘pumping’ sound.
Gating
Another dynamic processor is a gate. A gate is “a process for controlling the dynamics of a sound. Gates reduce the volume of a signal once it drops below a threshold.”
In other words, a gate cuts out the quietest sounds, or any sound that falls below a threshold.
Much like a compressor, a noise gate has a threshold at which the effect is engaged. However, there is no ratio so to speak – the gate is either on or off, so the signal is either cut or not. The diagram above to the left shows the raw original signal, and the diagram to the right shows that the signals that fall below the threshold (black line) are cut.
To the right is a gate graph, showing that there is no output until the input level reaches a certain point.
Gate parameters
Threshold: the point at which, in dB, the gate is disengaged (once the signal is loud enough the pass the threshold)
Attack: determines how quickly the gate opens.
Release: determines how quickly the gate closes.
Hold: how long the gate stays open for after the signal is below the threshold again. Helps to make sure that the decay portion, or ‘tail’, of sounds aren’t cut off.
Range: allows the signal below the threshold to be ‘turned down’ in volume rather than cut completely.
Example of Gate Plugin
Reasons to use a gate
Due to the fact that they cut out the quietest sounds, gates are often used to reduce background noise, like hum, or to help eliminate spill from other instruments (if recorded in a live setting).
A close relative of the gate is the expander. Expanding is “a process for controlling the dynamic range of a sound. Expanders increase the dynamic range by making quiet sounds even quieter; they do this by reducing the volume of anything that is below a set threshold level.” An expander will just reduce the level of any signal below a threshold, rather than cut it like a gate does.
If you want to know more about the difference between gates and expanders, give this article a read.
Side-chaining
Side-chains feature on both compressors and gates. Here is the Edexcel definition of what a side-chain is: “an input that allows the processing to be triggered by an external source.”
When you use a gate or a compressor, the plugin monitors the level of the selected channel and controls the volume of that same channel. However, when you use a side chain, it monitors the selected channel and then controls the volume of a different channel.
To give you an example, you might apply a compressor to a percussion channel and side-chain it to a synth. As shown in the diagrams above, whenever the signal from the percussion channel exceeds the threshold (eg. when a snare is hit loudly), the signal from the synth channel is reduced in volume.
It can be a bit hard to imagine what this sounds like but I always think of when radio DJs talk over the songs that they’re playing. Whenever they go to the mic to say anything, the song immediately dips in volume so that the DJ can be heard clearly over the top.
There are a few reasons why you might want to apply a side-chain:
It creates space within your mix – with a light compression, you can make it easier for the vocals to sit on top of the mix without the other instruments fighting for space.
Make the kick drum ‘punchier’ – in the lower end of the frequency spectrum, the bass can often mask some of the kick drum. To make the kick more prominent, side-chain your bass to a compressor.
To add weight to your kick drum – another way to make your kick drum more impactful if to apply a gate to it and side chain with your bass guitar. This way, the bass guitar is cut when the kick is silent and is only audible when the kick is played.
Popular in EDM – compression side-chaining can add a pulsing, more rhythmical quality to the sound.