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ART Levelar

Vactrol Levelling Amplifier By Paul White
Published March 1997

Paul White puts the squeeze on ART's new baby valve compressor.

It doesn't take much guessing to realise that Levelling Amplifier is a euphemism for compressor/limiter, but Vactrol isn't, as you might imagine, a designer drug designed to help you relax. Vactrol are actually an electronic components manufacturer specialising in opto‑electronic devices, and ART's new baby comp/lim combines a Vactrol LED/photo‑resistor with the low‑voltage tube stage first used in ART's Tube MP mic preamp. The idea is to recreate classic opto/tube compressor characteristics at a relatively low cost, and at the same time make the unit very easy to use.

Packaged in the same tiny box as the Tube MP, the Levelar is a single‑channel processor with both balanced jack and balanced XLR audio connections, though you can also use it unbalanced simply by patching in an unbalanced jack lead. Power comes from the familiar, but nonetheless infuriating, external adaptor, though the designer has at least included a little U‑shaped punch‑out in the metalwork which allows you to secure the cable, making inadvertent disconnection less likely.

The only controls on the Levelar's front panel are two knobs and three buttons, and there's also a 4‑section LED gain‑reduction display. Threshold is variable from ‑30 to +10dB and the other rotary control, Output, supplies make‑up gain to a maximum of 12dB. Whereas most compressors have further knobs for attack, release and ratio, the Levelar rationalises this to a 2‑position Limit/Compress switch, an Auto/Fast release switch and a Bypass button. Limit/Compress switches the compression ratio between 2.3:1 and 6:1. Attack is preset to a comfortable 6.5ms, and in Fast mode the release time is 200ms, making this a good general‑purpose setting. Auto release brings in a program‑dependent release time of between 70ms and 1 second.

The gain‑reduction meter comprises four LEDs, the first of which comes on when the level hits threshold, and the remaining three indicate 3, 6 and 12dB of gain reduction. A further green LED shows that the unit is powered up.

In Use

I have to say that this compressor is the easiest to use I've ever come across, and it actually sounds quite sweet. Much has been said about the disadvantages of running valves at very low voltages to 'fake' the valve sound, but I've heard a number of so‑called starved tube circuits that actually sound rather nice — and this is one of them. In Compress mode, the ratio is fairly low, so you wouldn't expect to hear too many side effects. In fact, this setting provides very smooth compression with no loss of transient detail; the tube circuit adds in a little 'thickness' to the sound, but not enough to make it seem treated.

Limit starts to knock the sound around a little if you pull the threshold down far enough to initiate a lot of gain reduction, but in many cases this is exactly the effect you want, to harden up rock vocals or add snap to basses and drums. Indeed, if you really pile on the compression, things start to pump quite nicely, but the sound always stays musical. At lesser settings, the limiter is reasonably transparent, though to me it seems best when it's just starting to sound as if it's working for a living. Having an output gain control makes it easy to balance up the levels so that you can use the Bypass button to compare the processed and unprocessed sound.

I suppose what I have to decide is whether the simplification of facilities has gone too far, and I guess that, being really honest, I have to say that more control over ratio would have been useful. For some material, the Comp setting is a little too gentle, whereas Limit is just a hint too tough, but on the whole the Levelar is rather more flexible than it first appears. Interestingly enough, I didn't find the lack of attack and release controls at all limiting — the Auto setting in particular is very flexible.


Obviously, the Levelar isn't going to give you the same pedigree of sound as one of the high‑end, all‑tube compressors, and it doesn't have the flexibility of a typical studio compressor, but what it does deliver is a warm, musically attractive sound that works well on vocals, bass guitar, drums, and even complete submixes. The simplicity of the controls is generally more of a help than a limitation, though I'd have liked a third ratio setting somewhere between the two on offer — a variable ratio control would have been even better.

Because the Levelar is a single‑channel device, it isn't able to process stereo mixes, but it is well suited to project studio applications where you need to add a little valve warmth and vintage compressor thickness to the odd vocal or instrument line. It's also an ideal compressor for people who don't have much previous experience with compressors, as it's very easy to set up and use. Given its low cost (for a valve processor), and its ability to produce musically satisfying results very easily, I wouldn't be at all surprised to see the Levelar appealing to a wide range of users.


  • Affordable.
  • Easy to set up.
  • Warm, classic sound.


  • Limited controllability, especially Ratio.
  • No stereo linking facility for two units.


A simple compressor based on valve and photocell technology which combines gain control with subtle tonal enhancement.