Undertone Audio UTEQ500

With a chameleon‑like ability to replicate the curves of almost any analogue bell or shelf EQ, this has to be one of the most versatile equalisers out there.

The UTEQ500 is a three‑band EQ, and yes, I know you’ve all used those before — but not one like this. Because, despite having only six dual‑concentric knobs and a few toggle switches to play with, the UTEQ500 is probably the most versatile ‘console‑style’ analogue equaliser I’ve ever had the pleasure of testing. A solid‑state design from UnderTone Audio, this single‑slot 500‑series module is electronically balanced, and the filtering is performed using resistor‑capacitor networks. With no transformers or inductors at play, it won’t surprise you to learn that it doesn’t sound ‘vintage’ in terms of harmonics and saturation. Rather, it’s all about the curves and the way you can manipulate them, though there is still definitely a sweet spot into which you can drive it for a little ‘crunchy’ attitude if you like to do that.

Basics

All three EQ bands are identical, other than that they operate in different frequency ranges. The frequency is determined using a pot rather than switches, so you can set each band freely within its range. Each band can also be engaged/bypassed independently. The high band, at the top of the module, runs from 1.4 to 22 kHz; the mid band controls are switchable to operate in either a low‑mid (90Hz to 1.4 kHz) or high‑mid (390Hz to 6kHz) range; and the low band frequency control covers 20‑340 Hz. There are also small toggle switches that allow you to set each band to boost, cut or notch — more on that below.

All of the six knobs are dual‑concentric types. That’s a good call on a 500‑series module because, as on a console, panel real estate is a precious commodity, and this choice permits lots of functionality to be accommodated while still allowing access for large fingers and thumbs. Of course, it also means that there’s more going on here than first impressions might suggest, and if you’re one of those who likes to dive in without reading up on what the controls do, you might like to approach this particular EQ differently.

The outer knob on the left of each band is its gain control. This is marked from 0‑10 rather than in dB, presumably so that the legend is uncluttered and relates meaningfully to the inner knob as well as the outer one. The gain pot can be set anywhere from 0‑15 dB, so with the boost/cut switch, the total range is ±15dB. When in notch mode, though, it can go deeper still, as I’ll discuss below. The outer knob of each band’s control on the right is the frequency selector. Then we have the inner controls, with the blue‑capped one on the right being a Q (bandwidth) control and the black‑capped knob one a Shape control.

At its fully anticlockwise position, the blue Q control gives you its widest bandwidth, with a Q of 0.3 delivering generously wide, gentle curves. At the opposite extreme you get what, for analogue hardware, is a very surgical Q of around 10. So with just the two outer controls and the blue inner one, you already have a pretty conventional three‑band analogue parametric bell EQ.

Shape Of U

To use it in that way, you need to set the black Shape control fully anticlockwise. And it’s when you start twisting the Shape knob that things start to get a bit less ordinary. Apparently, this feature started life as an internal control on a prototype, so that Eric Valentine could decide how he wanted his EQ’s shelf to sound — most EQ designers choose what sort of curve they want in a shelf — but he had so much fun tweaking it that he felt it should go on the front panel as a user control.

In broad terms, you can think of Shape as a control that morphs the band between a bell and a shelf. Taking the low band as an example, let’s assume you’ve dialled in a boost Shape fully anticlockwise: a plot of the frequency response would show a bell shape, falling off either side of the chosen centre frequency. But as you then start to turn the Shape control clockwise, everything below that band’s centre frequency begins to be lifted, while everything to the right remains as it was with the bell boost. Keep turning, past the point at which the curve resembles a conventional shelf, and you start to modify the shape of that shelf, with the selected frequency dropping while the shelving boost remains. Take it further towards fully clockwise, and you’ll introduce a small dip just above the selected frequency, after which the curve rises to give you your shelf — a shape that’s reminiscent of some classic vintage EQs, but here it’s much more controllable. Finally, throw in the Q setting, which remains active for both bell and shelf alike, and the three bands, and you can achieve some pretty radical curves indeed. For instance, with narrow bandwidths you can get huge, narrow boosts and cuts either side of the selected frequency, and very steep slopes on your shelves. Once you know how to drive this thing, you can do some pretty cool things to sculpt the low end with just a single band, and that still leaves you with two more bands to throw at the signal. So it’s powerful, hugely versatile stuff.

If you want tangible examples of just how versatile it is, it’s well worth checking out Eric Valentine’s ‘deep dive’ video on UnderTone’s YouTube channel. In this, he demonstrates the UTEQ500’s ability to almost perfectly match the curves of the Pul‑Tec, Neve and API EQs that he’d used on a demo mix. There are some differences when looked at on an analyser, but they’re vanishingly small. (While there are sonic differences, it also goes to show just how much the EQ curve contributes relative to the harmonic distortion ‘character’ of an EQ).

Curve Learning Curve

As part of my review tests, I attempted to do something similar and, working with an analyser to visualise and compare the curves, I was able to match some of my own hardware EQ settings pretty closely. It has to be said, though, that when ‘flying blind’ and relying exclusively on my ears, the different control sets of different EQs always tend to lead me toward slightly different (albeit equally valid) decisions, and this EQ is no exception to that. As I worked with the UTEQ500 on more material, I soon got into the habit of dialling in a pretty basic bell boost/cut with a reasonably wide bandwidth as a starting point, and then manipulating the Shape and Q controls, in that order. I found this a pretty reliable way of getting things where I wanted with the UTEQ500. You might find that a different tactic works better, but the point is that there’s a learning curve to this thing: with such radical EQ shapes possible, you’ll want to take a while to figure out an approach to using this equaliser that allows you to dial in the sound you want quickly.

Super Notch

You’ve probably noticed that I’ve not really said much about the notch filter setting yet. A notch filter is a pretty rare feature on a console‑style equaliser, yet the ability to surgically cut out an offending frequency can sometimes be really useful — and with this one, you can cut by over 50dB, pretty much eliminating the selected frequency. The resonance (Q) control is still in play in Notch ‘mode’ too, allowing you to make the cut as wide or narrow as you want.

The UTEQ500’s notch filter doubles up as an all‑pass filter — and that’s really cool!

While that’s all pretty cool, the UTEQ500’s notch filter doubles up as an all‑pass filter — and that’s really cool! This is possible because the UTEQ500 is a parallel EQ: the boost mode uses a signal that’s the same polarity as the dry signal, so augments it, while cut mode uses a polarity‑inverted version of the parallel signal, so subtracts from it. But for the notch, things are configured slightly differently. As you turn the gain knob, you start to bring in the notch filter, and by the time you reach the knob’s midway position, the notch is at its deepest. Keep on turning, and the notch recedes until, at the fully clockwise position, it once again has no impact on the frequency response, but the band is still polarity inverted. So when working with two signals, this gives you the ability to massage their phase relationship in a frequency‑specific way, allowing you to achieve sounds that you can’t simply by ‘flipping the polarity’ on one or other signal. It’s a wonderful tool for working with multi‑miked guitar cabs, or when blending more than one amp to achieve the desired tone.

Verdict

This might not be the most affordable 500‑series module out there, but I can’t think of anything else that does what this does, and you have to be really miserly to find anything to criticise — the best I could come up with is that there’s no power‑on indicator! So I suppose it’s bound to command a premium. Sure, some other EQs will sound a little different from this one, either because they have more bands or do more than just EQ: they may have transformers, inductors and/or valves that impart a certain character, for example. But I’ll bet they can’t do more in terms of manipulating a signal’s frequency and phase. You really can replicate pretty much any curve with just a few controls, and the notch and all‑pass filters are the icing on a very special cake. This is one of those ideas that’s so simple, yet so powerful that it makes you wonder why it’s taken someone so long to come up with it!

As I mentioned above, there is a bit of a learning curve to this thing, but once you have your head around it (watch the aforementioned video and you soon will) then not only does it become really easy to control, but you’ll probably find yourself leaning on this EQ more than your others. I should, I suppose, note that the UTEQ500 lacks any means of low‑ or high‑pass filtering a signal — but that’s by design, as UnderTone plan at least two more 500‑series modules, including a mic preamp and an additional EQ with a high‑ and a low‑pass filter plus an additional mid band. Pairing the two EQs would give you a full four‑band EQ with high‑ and low‑pass filtering. Again, that combination wouldn’t come cheap — though if this is out of your budget, you may like to know that Mr Valentine is rumoured to be working on a plug‑in...