How Does Dynamic EQ Work?
For those unfamiliar with Dynamic EQ, an easy way to sum up the concept is to imagine the typical controls for a compressor or expander built into the gain section of a normal EQ. So, with a Dynamic EQ you can adjust the frequency, bandwidth (or Q) and gain of a filter like you normally would. Where Dynamic EQ is unique is its additional controls for attack, release, threshold and ratio which determine how the source audio automatically adjusts the boost or cut of an EQ. These new controls can open up a number of creative and problem-solving EQ possibilities.
McDSP AE400 and AE600
The first dynamic EQ I came across was the AE400 by McDSP. This is a simple four-band EQ, offering fixed and dynamic EQ on each band. The AE400’s bands only offer classic bell shaped parametric EQs, but McDSP's new AE600 plugin increases the number of available bands to six. It also adds a variety of available filter shapes including, parametric, proportional Q, Baxandall shelving, vintage styled EQ and an X-style shelving EQ. Unique to both the AE400 and AE600 among dynamic EQs is a ratio control. This is a useful feature to help fine tune how the EQ cut or boost reacts to your audio. The stand out feature on both of these plugins is that they have very low latency and are very efficient when it come to CPU usage. These features seem to be a hallmark of a lot of McDSP's plugins and they are valuable if you are running a lean computer or trying to add one more plug-in to a huge CPU hungry mix.
Another great option is the dynamic EQ module found in iZotope’s Ozone. Ozone’s dynamic EQ controls include threshold, attack, release, dynamic gain, static gain offset and an inverse mode, which turns the compressor-like behavior of the controls into an expander. While Ozone is marketed with an ear towards mastering engineers, there are a few unique features that are beneficial throughout a normal mix session, too.
The first feature I’d like to highlight is Ozone’s ability to do mid-side, or M-S processing. Think of M-S as multichannel left - right processing, but instead of adjusting the EQ of the left or right channel on a stereo source, you are adjusting the middle and sides. The middle will be any information common to both speakers, and the sides will be any information that is different in both speakers. I love using this feature across my stereo sub groups within a mix. One recent application was using Ozone’s dynamic EQ in Mid-Side mode across a guitar sub-mix. I set a slight dynamic EQ cut in the mid rage of the guitars, on only the middle channel of audio, leaving the sides untouched. The guitars were sharing some midrange space with the vocal which was panned dead center, and the dynamic EQ let me keep that center guitar mid-range under control, while embracing the nice midrange guitar brightness heard in the side channels.
A second unique feature in Ozone’s dynamic EQ module is that it lets the user choose between analog-style minimum phase filters, and digital linear phase filters. Analog style filters create a shift in phase response, which can be good or bad, depending on your EQ needs. Digital linear phase filters don’t add any phase shifting artifacts, and thus can be a useful option for some applications such as surgical EQ moves. Be aware, they can also be a little CPU intensive, so you may want to use sparingly.
The final feature in Ozone that I end up using on almost every mix is their fantastic sounding Baxandall high- and low-shelf filters. Baxandall shelves are super smooth filters with a gentle slope. They can be a very transparent sounding filter shape, and I love using it to add high frequencies or air to a vocal. Having dynamic control can be a real bonus when doing high boosts because it allows me to boost some vocal high end, but then set the filter to turn the boost down if the high end begins to get a little too loud. This is a great way to keep vocals bright and airy but then ride down the level automatically when the high end gets a little loud. This is a really helpful tool for making sure a sound doesn’t get too fatiguing. The Baxandall shelf is also fun to use in Ozone’s inverse mode, adding extra high end only when a signal goes past the threshold.
iZotope also has a dynamic EQ option built into their new Neutron channel strip plug-in. Neutron has some amazing features beyond EQ, including a compressor, exciter, transient designer, and limiter. I’d like to touch on some of my favorite dynamic EQ features here.
The first cool feature worth noting is that the EQ’s eight parametric bands, and two shelving filters, can each be switched into dynamic mode independently. Having a quick and easy way to access a dynamic EQ filter within a channel strip plug-in is pretty amazing for my workflow. It saves having to pull up separate plug-ins and helps keep the creative mental mixing state flowing. Control wise, Neutron is pretty streamlined offering only a threshold level, and a button for choosing between compression or expansion. There is no independent attack or release control here because Neutron’s dynamic EQ is program dependent and based on the frequency selected for the particular band. Where Neutron’s dynamic EQ really sets itself apart is when it comes to sidechain routing options.
By default, a dynamic band uses itself as the trigger for any gain changes, so, for example, if a parametric dynamic band was set to 2.5kHz, with a Q of 3, the trigger would be the audio passing through that exact band of the EQ. Beyond the default setting, Neutron lets you set the sidechain to any other band of the EQ, or to an external source. On top of that, you can also set the external side chain to be the full bandwidth source, or to be filtered through any of the EQ’s bands. Another super useful feature is that if an EQ band is disabled, you can still use it as a side chain input!
All of these routing options may seem complicated, but I’ve got to hand it to the people at iZotope because navigating these features is very intuitive within Neutron’s GUI. To give you an example of how all these crazy side chain options might become useful, let me share how I recently used Neutron to sculpt the sound of an overhead microphone.
I was mixing a drum kit recorded with minimal microphones, and relying heavily on the overhead for the main tone. As I dug into the mix, there were some frequencies that bothered me when the kick hit, but I liked these frequencies when the snare hit, and vice versa. Using two different side chain options, I was able to trigger a dynamic EQ on the overhead track to have different settings for when the kick hit and the snare hit.
First, I wanted to cut some lower mids out when the kick hit, so I set one band of the EQ to the offending frequency range. Then I flipped it into dynamic mode, and set the side chain to be Internal Band 1. With Band 1 disabled, and now only acting as a side chain, I focused it down on the sub bass frequencies that were only happening when the kick was played. Now, the subs of the kick drum were triggering the lower midrange gain reduction.
For the dynamic EQ on the snare hits, I enabled two dynamic bands and triggered them with an external side chain set to the snare drum’s close mic. One band I used in compress mode to cut some mid range that was bothering me, and the other I used in expand mode to boost some top end whenever the snare was played. The end result sounded great and the possibilities that were available to create the final sound highlight the impressive features that Neutron provides for the engineer’s tool kit.
Soothe, Neutrino and Surfer EQ
Moving on from some of the standard dynamic EQs, there are a few more plugins taking the basic concepts we’ve been talking about, and pushing them into some interesting new territory. The first worth mentioning is Soothe by Oeksound.
Oeksound’s Soothe is a dynamic EQ that is tailor-made to help tame certain frequency resonances that can become annoying or harsh. Soothe’s self-adjusting frequency bands analyze audio in real time, and adjust its notch filters to catch each annoying peak as they happen. This process can be a boon to engineers struggling with cymbals with odd overtones or a vocal with lots of sibilance. It’s also great for those pronounced peaks in annoying midrange areas.
Another plug-in designed to automatically fine tune the spectral balance of a sound is iZotope’s Neutrino. Neutrino is available as a free standalone plug-in, and also included with Neutron as an integrated option within the channel strip. iZotope calls what Neutrino does “spectral shaping”. They describe it as something of a cross between a dynamic EQ and a multiband compressor with dozens of filter bands, each with independent adaptive thresholds based on the incoming audio signal. The end result is a process that aims to tame the frequencies that lead to excess peaks. This should, in turn, lead to a smoother, more balanced sound. Neutrino has four modes: Voice, Bass, Instrument, and Drums. The names are pretty self-explanatory, as each mode optimizes Neutrinos processing for sounds in those categories
Finally, I’d like to mention one more EQ that is dynamic in a completely different way. While we’ve thus far focused solely on EQs that dynamically change the cut or boost of a filter, Sound Radix’s SurferEQ goes in a totally different direction and dynamically changes the frequency of the filter. SurferEQ tracks the pitch of a monophonic instrument or vocal source in real time, and adjusts the frequency of the EQ to follow the pitch of the audio. This seems like it could lead to some pretty interesting EQ options, for example boosting the fundamental or cutting a weird dissonant part of the frequency range, and then having those EQ moves change with the pitch of the instrument. Another cool feature is that MIDI notes can control the pitch tracking, allowing the EQ bands to be played using a MIDI controller keyboard. Playing an EQ with a keyboard seems like it could lead to some wild new sound bending possibilities!
In closing, Dynamic EQ really is a cool new frontier in the world of signal processing, and can be a fantastic tool for both problem solving and wild sound creation. Let me know what kinds of applications you have for dynamic EQ in the comments below. Also, post a comment if there are any other cool dynamic EQs you love using.