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NTI Nightpro EQ3D

Dual-channel Equaliser By Hugh Robjohns
Published October 1997

High‑quality equalisers have the magical property of allowing you to tweak tonal content, while themselves remaining practically invisible to the ear. Hugh Robjohns checks out a contender from an American company new to the UK market.

The NTI Nightpro EQ3D is an equaliser — a dual‑channel, 6‑band equaliser. Those few words might appear dull enough to encourage you to turn the page in search of something with lots of flashing lights, pages of set‑up menus or a MIDI port, but in this case, that would definitely be your loss!

The EQ3D is not just an ordinary equaliser; it offers something a little unusual in the way of equalisation: sheer musicality. This EQ manages something that few others achieve, intended to serve as a mastering equaliser, allowing gentle 'sound tailoring' to breathe some top‑end life back into a tired mix, or give a gentle bloom and weight to the low end. What it won't do is cure a honking PA system, or notch out the hum from a guitar amp.

It has often been said that a really good equaliser cannot be heard. I'm not sure I completely support that point of view, but certainly it's possible to apply extraordinarily large amounts of EQ with the EQ3D before it becomes obvious. The inclusion of Nightpro's 'AirBand' high‑frequency shelf section also produces far better results than cheap enhancers when it comes to putting the brilliance back into a recording.


The EQ3D is housed in a 1U rackmounting box which is a slim 195mm deep. The top and bottom panels can be removed (after releasing a multitude of screws) to provide access to the internal circuitry and a couple of configuration jumpers.

The rear panel is extremely simple: just a pair of male XLRs for the outputs, a pair of female XLRs for the inputs, and an IEC socket for the mains electricity. The EQ3D features a switched‑mode power supply which can accommodate both 110V mains or the UK 240V rating.

The unit is shipped with the audio connections configured for unbalanced operation, but it's a simple matter to move a couple of jumpers inside to provide full electronic balancing of inputs and/or outputs, as necessary. The majority of my testing was carried out with the unit in balanced mode, but there was virtually no practical difference between the two formats in terms of audio performance.

Internal construction is to a very high standard, with components mounted on three circuit boards: one for each audio channel, and a third for the switched‑mode power supply. Components are of good quality, and the active audio electronics appear to be made up entirely of the industry‑standard NE5532 operational amplifiers. The supplied specifications claim an overall bandwidth of 5Hz‑330kHz (‑3dB points), a signal‑to‑noise ratio of 90dB, and total harmonic distortion of 0.005% — all of which is very respectable indeed.

The front panel is painted a very attractive electric blue colour, with silver labelling and graphics. A rocker‑style power switch is placed at the extreme right‑hand side, and there are two complete sets of colour‑coded controls (one set for each channel), with independent bypass buttons in the centre of the unit. There's no provision for accurate stereo linking between channels, and I would not recommend the EQ3D be used on stereo material. I found it hard to match settings between channels (especially with more extreme settings) and the inevitable result of this is blurring and instability in the stereo image.

Spindles With Knobs On

Each channel boasts five independent EQ bands (all offering up to 15dB of boost or cut), plus the AirBand, which is boost only. Each section has a low Q‑factor (to minimise phase shifts — a key part of the sound quality of the EQ3D), resulting in a broad bandwidth of about 2.5 octaves. This wide bandwidth of each section, combined with their frequency spacing, ensures that they overlap each other nicely, and will interact smoothly to produce many different and musical tonal variations.

The leftmost control for each channel is the 'sub‑band', which is centred on 10Hz and has a black knob. The adjacent bands (with blue, green, and red knobs respectively) are centred on 40Hz, 160Hz, and 650Hz, and these all have bell‑shaped symmetrical responses. The next band is centred on 2.5kHz, with an orange control knob, and this has a high‑frequency shelf response (ie. everything about the turnover point is lifted or reduced).

Unfortunately, none of these controls has a centre detent to define its unity gain position, although the scale around each knob is clearly marked from 5 to zero and back to 5 — zero being the unity gain position. However, the manual points out that because only very small amounts of boost or cut are normally needed, a centre detent on the knobs would be a hindrance rather than a help. After using the machine, I think I would agree with this philosophy.

Just to the right of the 2.5kHz control is a red peak overload LED which illuminates when the circuitry runs out of steam! In practice, you have to abuse the unit pretty severely to warrant illuminating it, and the EQ3D seemed to have more than enough headroom for realistic settings.

The last band is the AirBand, which also has a high‑frequency shelf response. Its yellow boost control is marked 0 to 10 (although it still only provides a maximum of 15dB boost), and the adjacent blue switch determines the turnover frequency. This last switch control is called VariAir and has six positions, which offer turnover frequencies of 2.5, 5, 10, 20 and 40kHz (plus an off position).

Places To Play

The EQ3D is a useful tool which brings benefits in a variety of applications. The most obvious one is in recording and tracking, where the unit can be patched between the microphone preamp (or inserted into the mixing desk's signal path) and the recorder. The manual also recommends using the EQ3D in mastering, broadcast, post‑production, live sound and home listening systems. I have a few reservations with these last applications — not because the unit wouldn't enhance the sound quality, because it almost certainly would have a beneficial effect — but because there is no stereo linking facility on the controls, as mentioned earlier.

I found the EQ3D worked best at the mastering stage, where I could tweak the overall sound character of a mix in a very subtle but surprisingly effective way. In cases where I would normally have plugged in a multi‑band compressor to thicken a mix up a little, I found the EQ3D could be used to produce similar results, but with a more open and transparent, and a less artificial, feel.

Using the EQ3D during mixing is a rewarding experience too. With careful setting up, the box really does help to open up the sound, and seems to capture a lot more 'life' than is normally possible with run‑of‑the‑mill microphones and preamps. With top‑end mics processed through the best mic preamps, I didn't feel the need to use the EQ3D during recording or mixing, but with more modest equipment the EQ3D was a real help and probably added about 50% to the apparent cost of the front‑end!

My favourite controls were those at the extremes of the frequency ranges — the 10Hz and the AirBand set to either 20kHz or 40kHz — but you need to be very careful, especially if you're recording onto DAT or a hard disk recorder (anything digital, in fact). The point to bear in mind when tweaking the frequency extremes is that you need to be able to hear what you are doing, and monitoring on limited bandwidth nearfield speakers can be very misleading.

Pulling up the bottom octave with the 10Hz control can add a beautiful warmth and weight on the right material, but can also produce speaker‑destroying rumbles on poorly recorded sources. A mix which initially sounded OK on a pair of nearfields shook my living room apart when auditioned on a pair of big transmission‑line speakers!

Excessive boost at the top end, particularly with the AirBand set to 20 or 40kHz, can cause all sorts of horrific problems with digital recorders — especially the earlier ones with baseband analogue anti‑alias filtering. Tracks which sounded bright, crisp and full of life on the monitors during the mix often sounded absolutely terrible on replaying the DAT, because of aliasing distortions. This was caused by relatively inefficient anti‑alias filtering letting a small amount of the high‑level HF signals into the recorder. This breaks the Nyquist rule prohibiting audio above half the sampling rate, and the result is anharmonic distortion of the most unpleasant kind. I found an old first‑generation Sony DTC1000 machine suffered the most from this phenomena, but a Sony R500 was very good in an identical situation. Modern A/D converters use a form of oversampling technology and accurate digital filtering to produce much more efficient anti‑alias filtering, and the R500 proved just how much better it is!

The moral is that you should be extremely cautious with the frequency extremes. Use only very modest amounts of boost at the low end, and if your monitors don't cover the full frequency range, err towards too little! Clues to look for are meter indications that seem too loud or don't appear to relate directly to the audible programme, and loudspeaker amplifiers that get surprisingly hot or run out of steam earlier than they should. As far as the top end is concerned, the same rules apply; monitoring through your digital recorder will reveal any aliasing problems.

The four middle frequency controls initially appear to be grouped at the bottom of the spectrum, but this is actually where the bulk of the audio energy lives and, in practice, the controls are very well chosen indeed. The range of subtle tonal variation that can be achieved is marvellous and always completely musical, apparently always working in harmony with the instruments. The bands work well together, and careful manipulation of adjacent bands makes an enormous range of control possible, allowing the desirable qualities and characteristics of most instruments to be drawn out.

Summing Up

This is without doubt a very useful tool which would inhabit the 'polishing and shining' drawer rather than the 'big hammers' drawer of the sound engineer's tool bench. It works best on material which has been very carefully and cleanly recorded, bringing out the very best qualities and making the whole mix sparkle and shine in a very pleasant manner. It will not make a lousy recording great, but it might make it less objectionable! Being something of an anarchist when it comes to sophisticated signal processing, I would much rather use the EQ3D to sweeten a mix than resort to enhancers and heavy multi‑band compression, and I think the end results would be better too. You will have to make up your own mind, of course, but I would thoroughly recommend you try it out.

Invisible Mending: The Airband

It may be unusual to see an EQ knob calibrated to 40kHz, but because the EQ3D uses bands which are 2.5 octaves wide, setting the AirBand to the 40kHz position with a lot of boost or cut will still affect audio components as low as 15kHz or so, and will therefore have an audible effect. If you subscribe to the theory that we can perceive frequencies above the nominal 20kHz that our ears are said to respond to, you'll love being able to experiment with the AirBand. If you don't subscribe to this theory, let's just say that you might want to re‑consider your views — I found it an interesting experience anyway!


  • Balanced or unbalanced operation.
  • Excellent sound quality.
  • Easy to use.
  • Very effective.


  • Lack of stereo linking.


A very well built and well designed equaliser. The extreme top and bottom bands are surprisingly effective, and the middle bands are perfectly placed to draw out the fundamentals and major harmonics of any musical instrument or voice. Great for polishing a mix and giving it a professional sound quality.