The Complete Guide To Dynamic Equalization/EQ


Dynamic EQ is a powerful and intriguing audio process/effect that should at least understood (if not regularly used) by audio professionals and amateurs alike.

What is dynamic audio equalization? Dynamic EQ is a type of equalization where the EQ of certain frequencies is triggered dynamically as those frequencies surpass a set amplitude threshold in the audio signal. Dynamic EQ, like a compressor, will have threshold, attack and release settings to alter the EQ of a signal dynamically.

In this article, we’ll discover what dynamic EQ is and how it works. We’ll consider the best practices of using dynamic EQ and the situations that call for it. We’ll also have a look at a few specific dynamic EQ plugins to confirm our understanding.


Table Of Contents


A Quick Discussion On EQ

Let’s quickly define EQ in a more general sense before getting into dynamic EQ specifically (click here to skip ahead to the section on Dynamic EQ).

EQ/equalization is a process in audio that changed the balance (relative amplitude) between various frequency bands within an audio signal. Equalization works by increasing or decreasing the level of some bands relative to other bands and effectively altering the frequency content of a signal.

The terms “cutting” and “boosting” refer to the EQ decreasing and increasing the relative amplitude of a defined frequency band, respectively.

Filters are typically thought of as processes that eliminate frequency content below, above or between two set frequency points. However, in the context of EQ, a filter can also be used to define the aforementioned boosting and cutting.

EQ is used in mixing, tone shaping, crossovers, feedback control and more. It is easily one of the most important tools for working with audio.

For more information on EQ in general, check out my article The Complete Guide To Audio Equalization & EQ Hardware/Software.


What Is Dynamic Equalization?

Now that we understand the basic idea of EQ, let’s consider the term “dynamic equalization”. On the surface, it sounds like a style of EQ that reacts dynamically to the audio signal. That’s actually exactly what it is!

Dynamic EQ is a style of EQ that has its bands (cuts and boosts) react according to the original (input) signal level within those bands. This is much different than typical EQ, which has a static frequency response.

So we can think of dynamic EQ as a typical EQ with dynamically controlled bands. Each dynamic band/filter (generally a peak/bell filter or shelving filter) will only be engaged to boost or cut the frequencies in question if the audio signal amplitude within that band is above a defined threshold.

If you’re familiar with compression, there are plenty of parallels between dynamic EQ and compression. In fact, dynamic EQ and multiband compression are often used for the same mixing applications.

The dynamic parameters of each band include threshold, attack time and release time.

The incoming input signal of the dynamic EQ is set to sidechain the dynamic processes of each band. As the input/sidechain exceeds the set threshold (typically set in dB), the band’s filter (cut or boost) will engage.

It will take an amount of time (attack time) for the boost or cut to be fully realized once the threshold is surpassed. Similarly, it will take some amount of time (release time) for the band to return back to “rest” or 0-gain once the input/sidechain drops back down below the threshold.

Note that, unlike compression, dynamic EQ has no ratio control (typically speaking) like compressors do. Dynamic EQ uses gain to dynamically alter its bands while compressors use ratios to calculate how much attenuation they apply to the above-threshold signal level.

In terms of EQ parameters, dynamic EQs are largely based on parametric EQs and generally have flexible continuous controls over gain, centre/cutoff frequency, Q factor and other parameters for each band.

We’ll get to the individual parameters in the following section. For now, let’s recap what dynamic EQ is.

Dynamic EQ is a style of EQ, largely based on the parameters of parametric EQ, that reacts dynamically to the signal it is equalizing.

Each band of a dynamic EQ is independent with its own bandwidth and gain. The dynamic controls are also set on a band-per-band basis, meaning that each band of a dynamic EQ also has its own threshold, attack and release parameters.

As the input signal within an EQ band surpassed the set threshold of that band, the band effectively “kicks in” and applies its gain across its bandwidth according to the shape of its filter.


Dynamic EQ Parameters

Dynamic equalization is a powerful and fairly involved audio process. There are plenty of “moving parts” in the design and, therefore, a variety of parameters worth considering when it comes to mixing with a dynamic EQ.

Here is a list of common (and mostly necessary) parameters of a dynamic EQ that may or may not be adjustable:

Note that the parameters listed above are effectively a combination of parametric EQ parameters and compressor parameters.

Also, note that this is not an exhaustive list of parameters that are found in any given dynamic EQ. Some units/plugins will have more or less functionality than we’ll define here. The parameters listed in this section are simply the essentials.

Let’s get into each parameter in greater detail.

Filter Selection

Each dynamically processed band of a dynamic EQ will have its own filter type. Generally, these filters will have a limit to the amount of boost/amplification or cut/attenuation they provide. Thus, peak/bell and shelving (high and low) filters are the typical dynamically-controlled filter types we’ll find in dynamic EQ.

Note that extreme bell/peak filter cuts will closely resemble notch filters and can be used for de-essing (removing sibilance from an audio signal).

Of course, low-pass and high-pass filters may be included as stationary/non-dynamic filters in a dynamic EQ unit/plugin. They may even be dynamically adjustable with the proper design.

However, for the most part, the filters used in conjunction with dynamic processing are those mentioned above (peak/bell, low shelf and high shelf).

What is a bell curve filter in audio? A bell curve filter is a filter capable of producing resonance (boost in EQ) or anti-resonance (cut in EQ) around a specified centre frequency. These filters are defined by a central frequency, Q factor (width of the boost/cut) and relative gain.

What is a low-shelf filter in audio? A low-shelf filter is a filter that either boosts (increases amplitude) or cuts (decreases amplitude) frequencies below a certain cutoff frequency. These filters generally have a well-defined transition band and a levelling-off of amplitude in the lower end.

What is a high-shelf filter in audio? A high shelf filter is a filter that either boosts (increases amplitude) or cuts (decreases amplitude) frequencies above a certain cutoff frequency. These filters generally have a well-defined transition band and a levelling-off of amplitude in the upper end.

For more information on low and high shelf filters, check out my article Audio Shelving EQ: What Are Low Shelf & High Shelf Filters?

For more information on the other filters mentioned above, consider reading the following My New Microphone articles:
• Audio EQ: What Is A Low-Pass Filter & How Do LPFs Work?
Audio EQ: What Is A High-Pass Filter & How Do HPFs Work?
Audio EQ: What Is A Notch/Band-Stop Filter & How Do BSFs Work?

Cutoff Frequency

The cutoff frequency parameter applies to shelving filters. It allows users to control the cutoff frequency at which the shelving filter will begin boosting or cutting.

The cutoff frequency marks either the -3 dB point of a shelving filter (if the gain is beyond the range of ±6 dB) or at the midway point if the shelving filter boost/cut is within the ±6 dB range.

Note that cutoff frequency also applies to low-pass and high-pass filters.

Centre Frequency

The centre frequency parameter applies to bell/peak filters. It allows users to control the centre frequency at which the gain of a bell/peak filter will be achieved and centred about (in terms of adjacent frequencies being affected).

Note that cutoff frequency also applies to band-pass and band-stop filters.

Gain

The gain parameter refers to the relative amplitude (boost or cut) applied to a band of a dynamic EQ. Gain is measured in decibels (dB).

Negative gain (attenuation) causes an EQ cut and positive gain (amplification) causes an EQ boost.

The set gain value will generally happen at the aforementioned centre frequency. Adjacent frequencies will be affected by a lesser degree within the band’s bandwidth/Q.

With shelving filters, the gain control will adjust the relative amplitude of frequency below a cutoff point (in a low shelf filter) or above a certain cutoff point (in a high shelf filter).

Note that the gain of any particular band will only be triggered as that band exceeds (or, in some cases, drops below) the band’s defined threshold.

Q Factor

The quality factor (referred to simply as “Q”) is a dimensionless value that determines the ratio of the centre/resonant frequency to the bandwidth of the filter.

Technically speaking, Q can be calculated with the following equation:

Q = fC / BW = √fHfL / fH – fL

where:
• fCcentre/resonant frequency
• fH: high cutoff frequency (where the signal drops off by 3 dB)
• fL: low cutoff frequency (where the signal drops off by 3 dB)
• BW: bandwidth

However, many EQs are either inaccurate or use a different method of calculating what they call “Q”.

The main concept to note is that Q refers to how narrow/steep or wide/gentle the boost or cut of the given filter/band will be. Regardless of the EQ, higher Q values produce a narrower band in which a smaller range of frequencies is affected.

Slope

The roll-off and transition band of a shelving filter can be defined by the slope of the shelf (typically given in decibels per octave or dB/oct).

The slope parameter control can alter the order of the filter in question, causing the slope to change.

Here is a table of filter orders (from 1st to 5th) and their respective slope here:

Filter OrderRoll-Off Per OctaveRoll-Off Per Decade
1st Order-6 dB/oct-20 dB/dec
2nd Order-12 dB/oct-40 dB/dec
3rd Order-18 dB/oct-60 dB/dec
4th Order-24 dB/oct-80 dB/dec
5th Order-30 dB/oct-100 dB/dec

Slope can also useful in defining high-pass, low-pass, band-pass and band-stop filters, though, as we’ve discussed, the slope is rarely dynamically controlled in dynamic EQ.

Threshold

The threshold parameter of a dynamic EQ is a set amplitude limit that dictates when the band’s filter will effectively engage and disengage. As the input/sidechain exceeds the threshold, the EQ band kicks in (with its given attack time). As the input drops back down below the threshold, the band disengages (according to its release time).

In other words, we have two situations:

  • Signal amplitude within the band is above the threshold: the band’s filter (boost or cut) is engaged.
  • Signal amplitude within the band is below the threshold: the band’s filter (boost or cut) is disengaged.

Lowering the threshold will allow an audio signal with lower amplitude in a given band to trigger that band into activation. If the threshold was set above the maximum amplitude of the input signal within the band, then the filter of that specific band would never be engaged.

Threshold is a key parameter in compression. To learn more, check out my article Dynamic Range Compression: What Is The Threshold Control?

Attack Time

The attack time parameter controls the amount of time it takes for a band’s filter to fully engage once the input signal amplitude surpasses the threshold.

The activation and de-activation of a dynamic EQ band’s filter are not instantaneous. It takes some amount of time to fully develop to the maximum boost or cut once the signal amplitude surpasses the threshold. This time is defined by the attack time parameter.

Release Time

The release time parameter controls the amount of time it takes for a band’s filter to fully disengage once the input signal amplitude drops back down below the threshold.

Once again, the activation and de-activation of a dynamic EQ band’s filter are not instantaneous. It takes some amount of time for a band’s filter to fully return to “off position” or 0-gain once the input signal drops back down below the threshold. This time is defined by the release time parameter.

Attack and release times are important parts of dynamic EQ and compression at large. To learn more, check out my article Dynamic Range Compression: Attack & Release Controls.

Other Parameters

It’s worth noting, once again, that the parameters listed above are not the only parameters that can be included in a dynamic EQ unit or plugin.

Some dynamic EQs offer more in terms of dynamic control (including ratio-like controls, knee controls, external sidechain etc.). Dynamic EQs may also offer other parameters that are unrelated to the functionality of the dynamic equalization portion itself.


How Are Dynamic Equalizers Used?

If you’ve made it this far, you’ve likely learned enough to know how powerful and useful dynamic equalization can be. Let’s discuss a few applications for dynamic EQ to further our understanding.

Dynamic EQ is a great tool to use for de-essing. If problem frequencies such as sibilance only pop up now and then, a dynamic EQ with a notable cut can work wonders to control the problem frequency range as it surpasses a given threshold.

This is effectively the process of “de-essing” but can be applied to frequencies other than those involved in sibilance.

Dynamic EQ is useful when EQing instruments with a wide range. If low notes and high notes are being played in the same piece, a static EQ may cause varying amounts of colouration as it affects the higher harmonics of some notes (lower notes) and the lower harmonics or even fundamental frequencies of some other notes (higher notes).

Since fundamental frequencies generally have greater amplitude, using a dynamic EQ on a wide-range instrument can, perhaps, more accurately compress the sound source according to the notes being played.

Dynamic EQ can also be used in many instances where multiband compression would be used.

In fact, dynamic EQ is sometimes preferred as it does away with crossover filters and the phase-shifts therein which may have a negative impact on the mix. Of course, EQ (unless it’s a linear phase EQ) will cause its own phase shifting. However, if only engaged lightly, a dynamic EQ will typically cause less phase-shifting than a multiband compressor.

So then a dynamic EQ can be set up to control the dynamics of certain bands with different controls, allowing more dynamic control over an audio track, bus or potentially even a master (though tread lightly).

Note that, just because dynamic EQ is useful, doesn’t necessarily mean it’s worth putting on everything. Dynamic EQ plugins will require more CPU to run than “regular” EQ plugins and overdoing it can lead to the overloading of the computer and DAW. If a “static” EQ will do the job, it’s often best to keep it simple and choose to use the plugin with lower CPU demands.


Dynamic EQ Vs. Multiband Compression

It’s been said, earlier in this article, that dynamic EQ and multiband compression are similar in their audio mixing applications. Before we jump into the section on dynamic EQ examples, I figured it would be a good idea to quickly go through the differences between dynamic EQ and multiband compression.

The differences can be summed up in the following table:

Dynamic EQMultiband Compression
Defines bands by filter type, centre frequencies and bandwidth.Uses crossover filters to separate bands.
Each dynamically-processed band has its own dedicated EQ settings and dynamic processing settings.Each band has its own dedicated compressor.
Uses gain to adjust the level of each band.Uses ratio to adjust the level of each band.
Has cutting and boosting capabilities.Only offers cutting. Would require expansion to offer "boost".
Typically has more available bands.Typically has few available bands.
Arguably more transparent (like EQ).Arguably less transparent (like compression).

Put simply, a dynamic EQ is an equalizer with dynamic control and a multiband compressor is a processor that splits an audio signal into several bands and provides an independent compressor for each band.

A dynamic EQ, as we’ve mentioned, is designed as a parametric EQ that utilizes the input signal as a sidechain source to trigger different boosts and cuts in the equalization.

A multiband compressor uses crossovers to split an input signal into several bands and treats each band with its own compression.

For more information on multiband compression, check out my article What Is Multiband Compression & How Do MB Compressors Work?


Examples Of Dynamic Equalizers

Before we wrap things up, it’s always a great idea to consider some examples. Let’s have a look at a couple of different dynamic equalizers to help solidify our understanding of this EQ type.

In this section, we’ll discuss:

BSS Audio DPR-901II

The BSS Audio DPR-901II (link to check for a price at Reverb) is a pretty flashy rack-mounted dynamic EQ. It is defined as a 4-band parametric Dynamic Equalizer that allows frequency-selective compression (cutting) up to -30 dB and expansion (boosting) up to +16dB.

Unfortunately, the BSS Audio DPR-901II has been discontinued.

BSS Audio DPR-901II

The BSS Audio DPR-901II can be set up as a single-channel 4-band dynamic EQ or a dual-channel/stereo 2-back dynamic EQ. The device can also be side-chained if need be.

Bands 1 and 4 can be switched between a bell and shelving filter while bands 2 and 3 can be switched between a bell and flat/wide-band response (narrow and wide Q). The width of such bands can be further defined via the width knob.

Each band has a frequency control to see the centre or cutoff frequency along with a Comp-Exp knob to control the maximum amount of compression/cutting or expansion/boosting. The compression or expansion ratio progressively increases as the knob is turned away from the centre and is soft-knee close to the centre, becoming harder (more like a limiter) with more extreme settings.

There is, of course, a threshold control for each band. There is also a switch to determine how the dynamic EQ interacts with the threshold. Each band can be set to EQ the signal when the signal level is above the threshold or, alternatively, when the signal level is below the threshold.

Sonnox Oxford Dynamic EQ

The Sonnox Oxford Dynamic EQ (link to check the price at Plugin Boutique) is a powerful EQ plugin that offers 5 overlap-able fully-parametric bands that react dynamically to the audio signal.

Sonnox Oxford Dynamic EQ

Each of the Sonnox Oxford Dynamic EQ’s bands can detect mono, left only, right only, stereo, mid or side channels and each comes with its own set of dynamic EQ controls including:

  • EQ type (low shelf, bell, high shelf)
  • EQ cutoff or centre frequency
  • EQ Q factor
  • Boost/cut amount
  • Threshold
  • Dynamics (similar to the ratio control of a compressor)
  • Attack time
  • Release time

Each band can be set to react according to peak or onset (similar to RMS) levels and can be triggered as the signal level either rises above the set threshold or drops below the set threshold.

Sidechaining is made possible for each of the bands as well. Furthermore, with the right settings, the Sonnox Oxford Dynamic EQ is also capable of upward and downward compression and upward and downward expansion.

To learn more about compression, check out the following My New Microphone articles:
• The Complete Guide To Audio Compression & Compressors
 What Are Compressor Pedals (Guitar/Bass) & How Do They Work?


What are the different types of EQ? When it comes to audio equalization, there are several types of EQ to be aware of. They are as follows:

What is the difference between dynamic EQ and multiband compressors? Dynamic EQ and multiband compressor are very similar in their purpose but differ in a few key ways, including:

  • MB compressors split the signal into bands before processing while dynamic EQs only affect the specified bandwidth of the filter in question.
  • Dynamic EQs can offer boosting while MB compressors cannot.

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