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Get Better at Compression – Advanced Controls Explained

Jun 05, 2024

What’s a Knee control? What’s Hysteresis? Here we’ll teach you how those lesser-seen controls on our compressor plugins work – and where to find each in the Waves catalog.

Get Better at Compression – Advanced Controls Explained

If you’ve got your head around the fundamentals of dynamic compression, great work; it’s hardly the easiest subject to gasp. Depending on the task at hand, sometimes you just need a fuss-free compressor like the Waves R-Comp that gives you Threshold, Ratio, Attack and Release controls, other times you may need a little more control over your dynamic processing.

But what do all of those extra compression settings do? The ones you’ve perhaps been ignoring up until now. In this article, we’re going through some of the more advanced compression settings you may have come across, explaining their purpose and how you can use them to refine your control over dynamics in your mixes.

Knee

As long as you’re up to speed on how Ratio and Threshold work in the context of compression, the term Knee should be relatively easy to understand. When a signal crosses your compressor’s Threshold, it begins to reduce the level of the signal according to the Ratio. The Knee refers to how strictly and abruptly the Ratio is adhered to.

Knee control in compressors

At 0dB or a hard Knee setting, the compressor will ignore the signal below the set Threshold, then will apply the full Ratio as soon as the signal crosses said Threshold. A soft Knee, sometimes measured in a decibel value, will begin to introduce compression more gradually as the signal nears the Threshold. The Knee differs from the Attack, in that it refers to the level at which the full Ratio is reached as opposed to the speed at which compression is applied.

So when might you use a knee control? Generally, soft knee compression tends to sound more subtle and natural which makes it suitable for gentle dynamic processing on signals with relatively low dynamic range. Hard knee compression will tackle dynamics more quickly, but may be quicker to cause distortion as a result. This makes it more suitable for highly dynamic signals such as drums or bass guitars. You can find a sweet spot between the two by using a medium knee value.

Range

The Threshold and Ratio controls are used to dictate the amount of gain reduction that your compressor is applying, but you can restrict the amount of reduction being applied using the Range control. Not all compressors give you the ability to control the Range, but some plugins that do include the Waves C6 and C4 and Linear Phase Multiband Compressor.

Range control in compressors

The Range control is particularly useful because it lets you dial back the overall effect your compressor is having on a signal, without having to manually change multiple parameters. For example, if there’s one particular syllable, guitar pick or drum strike that causes a noticeable ducking in your signal, you could automate the Range amount to make the dynamic compression more subtle.

Internal Sidechain (SC-HP)

If you already know your way around a compressor, you’ve probably explored the concept of sidechain compression, whereby an external signal is used to trigger the compression on a separate channel. As the name suggests, this process utilizes an external sidechain signal, but did you know there’s such a thing as internal sidechain processing?

Internal sidechain processing in compressors

Really, internal sidechain just refers to the signal being processed, but some compressors such as the Waves DBX 160 and Abbey Road RS124 let you process the signal that the compressor is responding to. Usually, a high pass filter can be placed in the signal chain before the compressor’s threshold. This is useful when compressing signals with a wide frequency range such as drum or mix buses, as it lets you remove some of the low end from the internal sidechain signal, resulting in more natural and subtle compression.

Auto-release

Provided you’re not totally new to dynamic compression (perhaps start here if you are), you should understand what Release is and how it works in the context of dynamics processing. While many compressors have a Release control, not all of them have an Auto-release. But what is Auto-release?

Auto-release control in compressors

Plugins such as Waves V-Comp have an Auto-release setting, which listens to the dynamics of the audio input and adjusts the release time accordingly. For example, quick and loud peaks will be compressed with a faster Release, while more sustained sounds will be compressed with a slower release. This can help you to achieve more transparent compression, making it a useful feature on sound sources with highly variable dynamics, such as vocals.

Analog

While the whole analog vs digital debate rages on, we’ve been hard at work developing digital tools that accurately emulate the character and tone of analog equipment that so many producers know and love. One of the main elements of digital software that people have become accustomed to, is the level of control that you get in the digital domain.

Analog modes in compressors

We’ve taken that a step further, and have equipped a number of our plugin versions of hardware classics with the ability to adjust the amount of analog essence being applied to your signal. The CLA-76, CLA-2A, CLA-3A, API 2500, V-Comp, Kramer PIE and H-Comp all grant control over different Analog modes and settings. Some compressors such as the SSL G-Master Buss Compressor simply have an Analog button, some plugins have a 50Hz or 60Hz setting, while others like H-Comp have multiple Analog modes to choose from.

After applying the relevant compression settings, try cycling through the various Analog character modes to see how they alter your sound. For more transparent dynamics processing, you can turn the Analog circuit off entirely.

Stereo Mode

Most Waves compressors come in two versions; a mono version with a single input and output, and a stereo version with a left and right input and output. But the stereo versions of some of those compressors, such as the Abbey Road RS124 and DBX 160 have further stereo controls.

Stereo Mode in compressors

In Stereo mode, the left and right channels are summed and compression is applied to both channels equally. Meanwhile, the controls for the left and right channels are linked, so if you change a setting on one channel, it will be mirrored on the other. In Duo mode, compression is applied to the left and right channels independently, and you can alter each channel’s settings separately. In M/S mode, the plugin lets you apply Mid/Side processing. This functionality gives you much more control over the stereo image, letting you process the dynamics of the centre separately from the sides of your signal.

L/R Link (aka Stereo Link)

Some compressors such as the API 2500 take the Stereo Mode explained above a step further, giving you even more control over how the compressor responds to the left and right channels. Using the L/R or Stereo Link function, you can adjust the amount at which the two channels are linked.

Stereo link in compressors

At 100%, the left and right channels are entirely linked and will apply compression to both channels equally. At IND, the left and channels will apply compression independently from one another. Try experimenting with Stereo Linking controls on audio with lots of dynamics in the sides of the signal, listening out for how it affects the perceived width.

Ceiling

This next setting is commonly found in limiters, as well as some compressors. The Ceiling refers to the absolute maximum level that a plugin will output, so if the signal entering your plugin is lower than the Ceiling value, the compressor will not apply any gain reduction. For that reason, you can think of a Ceiling as a kind of Threshold.

Ceiling control in compressors

You can also use the Output Gain control to reduce the level of the signal being outputted by a plugin, but this turns the entire signal down rather than setting the maximum output level. A Ceiling or Output Gain can be used to prevent your signal from going above 0dB, which causes clipping in the digital domain.

Lookahead

And finally, Lookahead, a control that enables your compressor or limiter to look slightly ahead of the signal, allowing it to begin gain reduction sooner. It works by applying a delay to the input signal, which is the signal that is compressed and outputted. However, the compressor listens to the non-delayed signal. For this to work and your signal to remain in time with the rest of your project, your DAW automatically applies delay or latency compensation.

Now you know what these extra compression settings do, you have no excuses not to give one or two of them a try the next time you open up a compressor plugin in a mix.

If you are looking to expand your compressor plugin collection, check out all the compressors we have to offer.

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