You are here

Behringer Ultra-curve

Signal Processor By Paul White
Published March 1996

Paul White plugs into the all‑singing, all‑dancing digital box that can perform graphic, parametric and shelving EQ functions all at once — and even handle real‑time room analysis and auto EQ'ing during its quieter moments...

Behringer have built their reputation on low‑cost analogue processors, and more recently, their Eurodesk analogue mixing console, but the Ultra‑Curve is their first foray into the world of digital signal processing. Because the Ultra‑Curve is a DSP audio processor, the only limit to flexibility is its software, so it isn't surprising to find features that would be prohibitively expensive to implement in an equivalent analogue device.

The Ultra‑Curve performs two main tasks: it can operate as a dual, 31‑band graphic equaliser with additional filtering, or it can be used as a real‑time room analyser. The audio path is 20‑bit, though the quoted signal‑to‑noise ratio of 108dB suggests that the actual resolution is nearer to 18 bits. The two internal DSPs are 64‑bit devices; hence the reference to 64‑bit in the product description. The sampling rate may be selected by the user, and though no digital I/O is provided as standard, an AES/EBU plug‑in option will shortly be available.

In addition to the graphic equaliser capabilities of the system, the Ultra‑Curve can generate high‑ and low‑pass shelving filters with variable slope, plus three further bands of fully parametric EQ, or a precision notch filter per channel. When used live, an automatic feedback exterminator function automatically deploys and adjusts the parametric filters to notch out troublesome frequencies whenever feedback occurs. Because digital circuitry doesn't take kindly to being overloaded, the Ultra‑Curve also includes a multiband limiter with a user‑variable threshold, plus integral noise gating. Provision has been made for an expansion option (the Delay 8000), to compensate for the distance between loudspeaker stacks in large concert systems, but as with the digital I/O, at the time of writing this is not yet available.

The system is fully programmable, and up to 100 user presets may be stored. MIDI control over both individual parameters and snapshots is available, and the user can select a crossfade time. This means that when EQ patches are changed, the filters change to their new values over a period of seconds, to prevent abrupt changes. This is potentially useful as a creative effect in the studio, where you can effectively morph between different filter programs.

The Hardware

Housed in a 2U, mains‑powered case with balanced jack and XLR in/outs, the Ultra‑Curve has a very simple front panel layout, the centrepiece of which is a large, multifunction 240 x 64 pixels LCD window. A single LED registers the arrival of any MIDI messages, and all the operations are controlled via just 12 buttons. The EQ and RTA functions have dedicated selector buttons, with a further button activating the relay‑driven 'hard' bypass, which connects the inputs directly to the outputs in bypass or in the event of a power failure.

The Setup button accesses a menu of the same name, where the usual utility functions are to be found. On the Ultra‑Curve, these include MIDI parameters, password anti‑tamper protection, LCD viewing angle, sample rate selection and so forth. The four buttons directly to the left of the display are soft keys, so called because their job varies depending on what screen is visible. Their functions are displayed down the left of the screen, though some of the functions are displayed by icon rather than name, and I'll be looking at these in more detail later.

To the right of the display are four keys arranged as a cross, and these function as cursor keys for selecting frequency bands, adjusting filter gains and any other functions that require the on‑screen cursor to be moved. Holding down an up or down cursor button will cause the appropriate value to step up and down, and in now familiar fashion, holding the opposite button down at the same time will accelerate this process. The Setup menu is used to select the sample rate of the Ultra‑Curve, which may be run at 32kHz, 44.1kHz or 48kHz. Unless you have the digital I/O option, there's no reason to use anything other than the fastest 48kHz sample rate.

In Use

The equaliser part of the system is the easiest to use, and other than the fact that you have to use the cursor buttons to move from slider to slider, and the up/down buttons to change the values, it operates much like a conventional graphic. All 31 EQ faders are graphically represented on screen, with a further fader to the right to control the master level. By hitting the Meter softkey, a pair of bargraphs showing both peak and RMS levels (switchable from input to output) is available, and the peak level is held so you can see whether or not you have any troublesome peaks. Because this is a digital system, it's very important that the peak input level is not exceeded.

The three parametrics provide full range coverage, and setting up is, once again, a matter of moving a cursor and using increment buttons. After using a system with knobs on, this is actually a real pain. I guess knobs were ruled out on cost grounds, but I know I would have liked using the Ultra‑curve far more if I didn't have to deal with an endless succession of button‑pushes. Another thing I found irritating is the fact that there is no printed frequency scale under the equaliser — so the only way to find out what's going on is to move the cursor to the band you're interested in, and read off the frequency and the amount of cut or boost.

The equaliser can be used in stereo link mode or as two monos, and if the stereo link mode is activated after both channels have been set up to different values, any further adjustments will be applied to both channels equally. If an adjustment tries to take any fader in the opposite channel past full scale, all the fader settings are scaled down to compensate.

In edit mode, you can load or save settings into 100 user memories, name patches or even opt to add or subtract the current EQ settings from a curve already in memory. Each patch memory contains the graphic equaliser, parametric/anti‑feedback and shelving filter settings, as well as the level, gate and limiter setting.

A spanner icon provides you with certain editing tools, including the option to reset to a flat line, though the parametric settings have to be accessed via the EQ setup button. A separate Clear function puts all the parameters in a patch to neutral — a good idea when you're starting a new patch from scratch. Using the loudspeaker icons, settings may be copied from one channel to the other. An EQ curve pictogram lets you choose a filter characteristic, either a bandpass or a pair of shelving (high‑ or low‑pass) filters — and this is on top of the graphic and parametric filtering. In shelving mode, the slope is variable in 6dB steps, from 6dB/octave to 30dB/octave. You can also directly compare the original loaded settings with any changes you might have made, using the A/B button.

Chasing Shadows

In a live situation, any or all three parametric filters may be switched to feedback suppression mode, in which case they lock onto feedback as it happens, and pull down the offending frequency band. If feedback then occurs at another frequency, the second filter steps in — it's quite interesting to watch the parametric parameters change on screen as this happens. Eventually though, you get to a situation where all three bands are being used, and then if feedback recurs at a different frequency, the first parametric goes after it, leaving the original feedback frequency unsuppressed.

I tried this to see how the system would react in a real situation, and as the gain is increased to the point of feedback, the filters deal with it very effectively. However, if you keep turning the gain up, the filters end up chasing the different feedback frequencies, so what actually happens is that the feedback keeps changing frequency, as first one, then the other feedback frequency is dealt with. In a real‑life situation, the system does offer a very real benefit, providing you don't pile on too much gain, though it's obviously not going to be as effective as something like a Sabine Feedback Exterminator, which uses far more filter bands.

Unusually for a graphic equaliser, the Ultra‑Curve also includes noise gating, which could be useful in the studio as well as in PA applications. This is a simple‑to‑use system, where only the threshold may be set by the user. Users wanting to employ MIDI control may use program changes to switch between programs, or controller information to regulate the individual bands, or the master level faders directly. No data is output over MIDI, so there is no way to store SysEx dumps of patch data, but a MIDI Out socket is fitted to facilitate future developments.

I checked out the EQ crossfade facility, and it worked smoothly with no sign of glitching, but handling real‑time switching from the front panel is tricky, because of the number of button presses required. There is no dedicated patch increment/decrement system — you have to go via the Edit menu. This being the case, MIDI control is pretty much essential for any creative purposes.


Given its relatively low cost, the Ultra‑Curve is a very sophisticated piece of signal processing equipment which, although designed with live music in mind, has a range of applications in the recording studio. The 20‑bit converters deliver an impressive 108dB signal‑to‑noise ratio. The equalisers, while lacking the charm of top‑end analogue equivalents, perform smoothly, without any obvious vices. The operating system is pretty straightforward, but the need to move the cursor along a row of 31 virtual faders obviously makes adjustment less straightforward than grabbing a fader. However, the additional features more than compensate for this, especially the additional parametric and shelving EQs, the limiter and the noise gates.

As far as creative potential is concerned, the ability to switch programs and control the master fader levels via MIDI means that you can use the Ultra‑Curve (via your mixer's insert points) to set up two very powerful channels of mix automation using your sequencer. The variable crossfade time allows you to set up some very neat filter morphing effects which, with more radical filter settings, can sound more like dynamic flanging than EQ. The RTA side of the unit is less obviously useful in the studio, other than for checking out your room and monitoring system, but it's a powerful tool for PA applications, as is the feedback suppressor. For larger PA rigs, the delay option means that spaced speaker towers can be time‑aligned, though I suppose you could use it with feedback from your mixer to provide a nice Shadows guitar echo at a pinch!

The main irritations are simple things like the lack of a printed scale around the display, a functioning MIDI Out, or a direct means of stepping through the programs from the front panel, without having to go via edit mode. Nor is there any direct readout of what patch number is currently active — but as this is a software‑based system, improvements can be added with later software revisions. Already, the manufacturers are looking at a MIDI master/slave setup for using multiple units, and PC‑based control software is also under development. Options include the Delay 8000 and the AES 8000 digital I/O, though from what the handbook implies, these are not user‑installable.

On balance, the Ultra‑Curve is a very proficient processor that brings digital EQ within reach of many more recording musicians, live performers and PA operators.

Room With A VU

The Real‑Time Analyser or RTA section of the Ultra‑Curve is mainly for use in live situations, but is also useful in the studio, both for learning something about the monitoring environment and for seeing what kind of spectral shapes different sounds have. An internal noise source generates either white, pink or sine wave test signals (pink is favourite for normal room measurement), while an integral mic preamp allows any mic with a flat response to be used to measure the result. Unfortunately, the phantom power on the mic socket is only 15V, which rather limits your choice of microphone. I managed to find a suitable back‑electret mic with a nominally flat response which would run from a 15V power source, and was reassured to find no gross anomalies in my studio when measurements were taken in and around the listening position.

In live situations, the RTA can be used to create a graphic EQ curve which is the inverse of the room measurements, so as to give a nominally flat response. Alternatively, one of the user memories may be selected as the target response. This helps improve sound quality and legibility when setting up a PA in a live venue, but I'd caution against doing this in a studio. Apart from the fact that EQ isn't the way to solve control room problems, I feel a system like this is far too open to misinterpretation to be used as a sound basis for control room equalisation. The RTA can give you a broad idea of what's right and wrong, but I wouldn't like to take it much further than that.

The RTA has a good selection of operational parameters and the results can be stored in ten user memories. Peak or RMS measurements can be made, and the decay time of the measurements can be set from 15ms to 1s, which has the effect of averaging the results over time to give a smoother display. The peak levels can be held and read off using the cursor buttons to move along the bands.

The Ultra‑Curve In Full

The Ultra‑Curve part of this system bears more than a passing resemblance to the BSS Smart‑Curve concept, in that the power of DSP technology has been brought to bear in an attempt to compensate for the interaction that takes place between bands in a conventional analogue graphic equaliser. With an analogue graphic EQ, the actual EQ curve may be quite different from that suggested by the fader positions, purely due to the degree of filter interaction that takes place, especially when adjacent sliders are set to radically different gain settings. While digital filters also interact, it is possible to largely compensate for this interaction, and the idea behind the Ultra‑Curve is that the EQ curve you see on the screen is the curve you get. The reason parametric equalisers are included is so that very steep filter slopes can be created by combining the effects of the parametric and graphic equalisers — but they're needed in any event, for the anti‑feedback part of the system.

The real‑time analyser section of the Ultra‑Curve proves third‑octave analysis to an accuracy of 0.25dB, and the Auto Q system enables the Ultra‑Curve to automatically adjust its own filters to compensate for venue acoustics and speaker positioning. When using Auto Q, you can select any one of the 100 user equaliser settings to be the target response, then Auto Q will endeavour to adjust the filters until the sound received back at the measuring mic corresponds to this ideal. An input is provided for a reference microphone, and the Ultra‑Curve can generate either pink or white noise, as well as sine tones for automatic measurement — though pink noise (equal energy per octave) is the usual way of making room measurements. Because not all reference mics are as flat as they should be, it's also possible to store a correcting EQ curve in one of the 100 memories, and use this to compensate for the mic response during measurement.


  • Very good value.
  • Clean audio path with smooth program crossfading.
  • Includes parametric, graphic and shelving EQ as well as limiting, gating, anti‑feedback filtering and real‑time frequency analysis.
  • Real‑time MIDI control possible.


  • All‑button operation makes the operation slower than ideal.
  • MIDI Out not yet implemented.
  • No permanent readout of the currently selected program number.


Though not ergonomically perfect, the Ultra‑Curve is fairly straightforward to use, and packs a lot of facilities into an attractively‑priced package.