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Review: Nugen Audio SEQ-S Plug-In

Linear Phase Equalizer 

Nugen Audio’s SEQ-S Spline Match EQ plug-in

The SEQ-S and SEQ-ST are the two models of Nugen Audio’s new linear phase equalizer plug-ins. The SEQ-ST is for mono/stereo/mid-side processing while SEQ-S works with up to eight channels of audio although, as yet, there is no Dolby Atmos version available. 

Both the SEQ-S and SEQ-ST operate exactly the same; the SEQ-S version is reviewed here. The SEQs are called “spline, match and morph” equalizers, and they run as Native plug-ins in AAX, AU, VST 2 and 3 format for DAW hosts, and in Mac OS X 10.9 or later and PCs Win 7 SP1 or later.

These equalizers use Fast Fourier Transform math rather than Infinite Impulse Response-based algorithms like most digital equalizers. Phase shift through SEQ is linear across the entire frequency range for a smooth, natural equalization, but at the cost of more processing delay or latency. A single stereo instance of SEQ-S will be 12,288 samples late and must be delay-compensated properly in your DAW. Compensation is automatic in Pro Tools HDX Ultimate or any modern DAW system. 

A Novel Approach

SEQ-S uses a unique and all-new approach to the equalization process. I found that to get proficient at using SEQ effectively required a learning curve. The manual makes a good quick-start guide.

The SEQ-S has a resizable GUI and allows using a mouse to directly draw the “spline” of a beautifully shaded EQ curve, called an EQ Envelope. An EQ spline has many consecutive Control points, or nodes, shown in a color of your choice superimposed over a matching color spectrum analyzer display. There are several choices for the spacing or banding of these nodes, with 1/3-octave as the default. As drawn, the spline is a curve that smoothly connects between points.

You may add, delete and drag existing Control points easily, and if you make an unintended change, there’s no limit to Undo/Redo. There are also both Highpass and Lowpass filters represented by very small triangles the same color as the EQ spline representing the cut-off point for these filters. They are hidden at the extreme left and right lower corners, and you have to “mouse over” them for discovery and use.

With this version, the analyzer display and its numerical scale values for amplitude (Y axis) and frequency (X axis) are too dim to see well, and there is no way to brighten them up. I always resized the plug-in as large as possible.

Assigning, Managing and Controlling 

There are three simultaneous color-coded EQ Envelopes available that are usable on any of up to eight channels in SEQ-S. Click on the Assign button and a routing matrix comes up to designate which EQ Envelopes are assigned to control which channel(s). The SEQ-ST variant could control L/R as one EQ Envelope, or the left and right or the mid and side components as separate EQ Envelopes. The stereo matrix/de-matrix process is automatic, and there is no way to control individual audio levels (in the plug-in) apart from just equalization. 

The Envelope Selector section in the middle of the GUI has three hide/show buttons labeled 1, 2 and 3 for managing the three EQ Envelopes. There are also three ON buttons that toggle the EQ Envelopes on/off and enable mouse control of its curve only, without inadvertently affecting the other envelopes.

Both the ON button and EQ Envelope must be lit up to change and hear that particular EQ Envelope. So you can show/hide all three envelopes but only control one at a time. Because each EQ Envelope is controlling a separate audio source, there is no resultant graphic representation of the algebraic sum of multiple EQ Envelopes.

Just above the Envelope selector is the Parameter Readout display. When hovering over a Control point using the mouse, the readout confirms both the frequency and that point’s boost/cut values.

But in the readout, Envelopes are given letters, so Envelope 1 is called “A” in the Parameter window. This is because the parameter readout also shows the particular number of the Control point—its numerical position from lowest to highest frequencies. In the default 1/3-octave banding, there are 30 control points from A00 at 21 Hz to A30 at 22.4 kHz. Chromatic banding has more than 1,200 control points! 

I thought it incomplete that there is no way to just type in a specific parameter value in the Parameter Readout window, as you can do with most digital EQs.

I had trouble inadvertently scrolling, zooming in/out, and adding extra and unwanted Control points until I found the Lock symbol in the Parameter Readout display. After inserting SEQ and before drawing any curves, I would first reset the plug-in and then click on the padlock to lock both L/R frequency horizontal (x-axis) scrolling and +/- vertical amplitude (y-axis) scrolling. Without first locking scrolling, using SEQ is hopelessly frustrating. Use Ctrl+Cmd+Click to reset to default both the horizontal and vertical scales.

Another helpful feature is called Zone. Zone uses two large white dots on the 0 dB axis line to put upper- and lower-frequency borders to prevent any changes outside the zone’s borders. You may also click Exclude and prevent any changes within the zone’s borders. The locked out zone(s) are dimmed in the display.


At the top of the GUI is a pull-down menu of advanced Banding choices that fixes the positions, or Bands, between two control points. There is a choice between: Thirds, or equal 1/3-octave bands (default); Sixths, or 1/6-octave bands (my choice for mixing); and Chromatic intervals, which offer the finest overall resolution. Finally, there are three Bark and Mel scale banding choices.

A Bark scale is the psychoacoustic measure of frequency divided into 24 bands that are equal in a physiological sense based on how well the human ear can differentiate frequencies. Looking at the 24 Control points while in Bark banding, you’ll see the bands come closer together, with more points in the mid-range from about 400 Hz to 4 kHz, where the ear is most sensitive. Bark Thirds doubles the number of control points for even more resolution in the midrange. And Mel banding is based on a different academic study.

Utility and Advanced Controls

Across the width of the top of the GUI is a row of Utility controls that includes the standard buttons for Bypass, Reset to initial bank settings, A | B and A to B, (B to A) memories, and full preset management system for Save and Recall.

Below this row are the Advanced controls for EQ Match, Curve Reset, Cut | Copy | Paste for control points, while the Invert button flips the polarity of the active EQ Envelope. Invert has become quite useful when applying proper subtractive EQ—SEQ is capable of boosting or attenuating up to 60 dB; once you find a problem resonance or noise, just click Invert. All digital equalizers should have invert functionality.

EQ Matching

EQ matching is a two-part process. Use the free Nugen Send utility to transmit audio from a reference track (in your session) to another track with SEQ-S placed on it. In this case, I wanted the EQ Envelope of a live drummer’s kick drum in place of the thin and small bass drum on another kit—there was no time to sample, trigger, replace and check accuracy.

Using the Send plug, I recorded and saved a few seconds as a “snapshot” of the live kick drum as reference. The Send Utility automatically routes the audio and mutes it from the mix bus. Next, I recorded a snapshot of the existing drum. Click on Match, and you’ll see the EQ curve instantly conform to the reference—it is like magic! 

Match EQ works especially well for audio with low harmonic complexity and minimal dynamic change. A great use is to create a “dip” in the entire track’s mix but only in the frequency range of the lead vocal. Once I recorded a snapshot of the track and another of the lead vocal, I inverted the results with the Invert button and, again, like magic, a section in the midrange frequencies was carved out corresponding to the lead vocal’s frequencies. 

To facilitate the SEQ’s EQ matching feature are the “D” and “S” controls. The Depth is a +/- control that changes all the envelopes’ intensities together like a Wet/Dry fader. The Sharpness up/down control works similar to a global Q for all EQ Envelope curves. Sharpness flattens/sharpens the curves and Depth is the strength of them. Both these musical controls are very innovative touches I found useful all the time when using SEQ. Again, more digital equalizers should have these very handy features.

EQ Morphing

Clicking the Morph button reveals another control bar to configure EQ morphing changes between temporary EQ memories resident in A and B. The Morph Play button is automatable like everything on SEQ, and, once you create an EQ Curve for A—let’s call it your “starting EQ”—and then your “destination EQ” in temporary B memory, you can program morphing between them.

You can set up (and automate) a one-shot single transition from A to B or from B to A. Return mode means one shot and back again, and Loop mode is morphing back and forth between A and B. The time period it takes to morph is based on session tempo in any subdivision or multiplication, or free running. Rapidly changing freely or in sync with your session opens up another avenue for sound design or special effect.

An excellent use for morphing is in post-production where the ambience of the location sound (artificial or natural) changes drastically in level, noise floor and room tone from scene-to-scene. Dialog editors could use EQ Morphing to lessen the abruptness of these transitions when editing between disparate scenes.

Reverb Effect

I was looking for a different and unrecognizable effect for a stereo pad. I split the stereo pad into two mono tracks panned left and right and put separate mono instances of SEQ-S on both sides set to morph between different A and B temporary EQ settings in each. I had the EQs loop morph at different tempo subdivisions of 115 BPM. Depending on the EQ differences between A and B and also the tempo differences, this produces an almost chorus-like or tremolo effect, but without any pitch change typical of chorus effects. This is a completely new effect that is controllable from subtle to drastically science-fiction sounding.

Mixing and Bark

Using Bark Thirds Banding and full-screen GUI makes it possible to focus microscopically on the midrange frequencies. I had a mix to do with a singer who pushed certain notes and intense moments up to 15 dB. Previously, through clip gain, automation, EQ changes and compression, I could manage to get her vocal to “sit” well in the track. That took a lot of time over the course of the entire mix.

I took all that processing off and started fresh using SEQ-S.


Taming the lead vocal in SEQ-S


For sculpting lead vocals, I like to view in Pre (but always hearing the applied EQ’s effect)—the incoming spectrum where I can see and hear the nasty bits and get confirmation of my changes on the Parameter readout. 

My singer had some nasty peaks at 2.3 kHz, 1.7 kHz, 1.1 kHz, and others but lesser so. When singing low, she had a big buildup (proximity effect or a wrong mic choice??) at 250 Hz. I put dips at all those specific frequencies and others—the biggest correction at -9.2 dB at 2.3 kHz! I liked to mouse over a spot (no clicking) to see what I had done and use both the Depth and Sharpness controls for fine-tuning this audio surgical procedure. This process took less time and sounded more natural and less “fussed with.”

Once I got the hang of using SEQ-S, I got comfortable using it as an everyday precision mixing/mastering EQ and effects generator. Every time I use it, I save what I’ve done as a preset. I feel like I am developing a good collection of great tools I can use over and over by just slightly tweaking my saved presets. 

SEQ-S comes with 22 factory presets that’ll get you close to all possibilities. On top of that, the linear phase SEQ-S is an awesome-sounding equalizer up to the challenges and worthy of any audio source. 

Product Summary

COMPANY: Nugen Audio

PRODUCT: Nugen Audio SEQ-S Linear Phase EQ


PRICE: SEQ-S $199; SEQ-ST $149

PROS: Powerful linear EQ that accomplishes miracles!

CONS: Dimly lit display, no way to type in EQ values, and poor manual