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SPL Dynamaxx

Compressor/ Decompressor/ Limiter/ Gate By Paul White
Published December 1997

SPL Dynamaxx

SPL claim to have come up with a completely new type of compressor. Paul White puts their assertions to the test.

Those of you who read the review of the SPL De‑esser back in the January '97 issue of SOS may recall that I was particularly impressed by the simplicity of its user interface — traditional de‑essers can be tricky to set up properly, yet the SPL model achieved excellent results with almost no experience required of the user. It now looks as though the company have applied the same philosophy to compressors, and though compressors with auto functions have been around for a while now, few are as easy to drive as this one. The DynaMaxx is a two‑channel, analogue compressor with balanced inputs and outputs on both XLRs and jacks (which may be used unbalanced without any signal level loss). Laser‑trimmed resistors are used in the input stage to provide the best possible Common Mode Rejection, which is quoted as 100dB at 1kHz and 80dB at 10kHz, and the overall signal path is very clean. There's a ground lift button on the rear panel, and each channel has an external side‑chain insert point on a TRS jack.

The gain control part of the circuit uses a pair of the new THAT 2181 VCA chips in a differerential drive mode configuration to provide a very low‑distortion signal path, and there's also an unusual Decompress mode to help repair the damage done through over‑compression by using upward expansion. SPL claim that the way this compressor works means that high‑frequency detail isn't lost when compressing with high ratios.

That Front Panel In Full

The control system is extremely simple, with rotary controls provided only for Compress, Gain and the on‑board Noise Gate. Other than that, there are just four illuminated‑when‑active buttons per channel, to select Soft Limit, Effect Compression on/off, Decompression on/off and bypass (Active). A further button links the two channels for stereo operation, and each channel has its own bargraph display to show the amount of gain reduction (or gain increase in De‑compress mode). Power comes in via an EC cable, and there's an illuminated mains rocker switch to the right of the front panel.

The Compress control sets the amount of compression taking place by combining the functions of threshold and ratio, although these also respond to the programme dynamics rather than remaining fixed. The outcome is that peak signals are processed with a higher ratio setting than lower level signals, and I imagine this has a similar effect to including a peak limiter. There are no separate attack or release controls, as these parameters are determined by the automatic circuitry and the dynamics of the input signal. Up to 20dB of make‑up gain is available from the Gain control, and Soft Limit brings in what SPL describe as a soft‑knee limiter to provide maximum control with the minimum of side effects.

Most people tend to use compressors in one of two ways: they either want transparent gain control, or they want to hear compression as an effect. The DynaMaxx gives you the choice by means of its Effect Compression button, which switches between the two alternatives. For an even stronger effect, Soft Limit can be used at the same time. The Decomp button turns the DynaMaxx into an intelligent upwards expander that can be used to increase the dynamic range of previously compressed signals in a subjectively natural way. The manual also suggest that this setting is useful for adding life to the sound samples used in synths and drum machines, as these are often heavily compressed. The Peak Limiter function also reverses in this mode to provide peak expansion, so switching in the Limiter will actually make the peaks louder!

The noise gate has just one control and one LED, labelled Close, but even this is smarter than it seems. Auto‑release circuitry matches the release time to the programme material, and the circuitry is claimed not to click. Finally, there's a green signal LED that comes on when the input signal exceeds ‑40dBu.

Using The Dynamaxx

As expected, using the DynaMaxx turned out to be exceptionally easy, but it still held one or two surprises. For example, when you go into Decompress mode, all the controls seem to reverse, including the make‑up gain, which becomes a make‑down gain. Although this is logical when you think about it, it's still odd when you first encounter it. There was also a noticeable click when the compressors were switched in and out of Active mode, though, to be fair, you're unlikely to want to change this switch setting during a mix.

In the straightforward compression mode, you can apply a surprising amount of gain reduction without seeming to change the sound at all, though your desk meters tell you that compression really is taking place. The meter works a little differently to most compressors I've tried, as the display comprises a moving block rather than a moving bar, and the dot's normal resting place in the absence of compression is determined by the output gain control. When compression is applied, the gain reduction is displayed relative to this position, not relative to zero.

...there's plenty of scope for creative abuse by applying enough compression to make the limiter work all the time. The limit action is relatively smooth, but the pumping that can be achieved through deliberate misuse has to be heard to be believed.

Switching in 'Effect' compression produced a thicker, more obviously compressed sound, but still very well behaved. You can make this setting pump if you apply a lot of compression, but at sensible settings, it just produces a denser, more even sound. If you really want to to see pumping, switch in the limiter, and then hit it hard. At moderate settings, where the limiter is acting only as peak protection, the sound is reasonably transparent, but there's plenty of scope for creative abuse by applying enough compression to make the limiter work all the time. The limit action is relatively smooth, but the pumping that can be achieved through deliberate misuse has to be heard to be believed. By using these three buttons in conjunction with different Compress control settings, it's possible to produce a huge range of compression effects, from virtually invisible to seriously blatant.

I've never had much luck using expanders on programme material before — they all seem to sound like noise reduction circuits that have gone wrong — but this one is remarkably usable. The signal gains more presence and more dynamic range, and it's only when you get silly with the controls that low‑level signals start to vanish and high‑level peaks hit you in the face. I don't know how often I'd use something like this, but it's nice to know that when you do need it, it's going to work smoothly and in a controllable fashion.

Finally there's the gate, which works so smoothly it's really quite boring. Providing you set the threshold sensibly, it will close down during pauses, quietly and unobtrusively, without chopping the ends off your decays. Even slow decays seem to get through unscathed. In a mastering situation, the gate is both fast and smooth enough to be used to clean up the starts and finishes of your songs, while the limiter can be used to keep peak levels from trashing your digital recording chain.


Once again, SPL have come up with something that's both effective and simple to use, yet just a little bit quirky to keep things interesting. I have never heard a compressor yet that can sound like any compressor you want it to, and this one certainly isn't going to change that situation, but by careful use of the deceptively small number of controls, you can approximate most types of compression used in track laying, mixing or mastering. I particularly like the ease of use, the smoothness of the processing, and the overall high quality of the signal path. My only technical criticism is the audible click when 'Active' is operated.

There's obviously a lot of processing going on inside the box to make the end user's job so easy, but because of its high‑quality signal path and overall flexibility, I think the DynaMaxx is going to appeal to a far wider range of buyers than those inexperienced users looking for a 'point‑and‑click' compressor.


  • High‑quality signal path.
  • Simple control layout.
  • Wide range of compression processes and effects available, including decompression.


  • 'Active' button clicks when operated.
  • The metering, while clever, could be confusing to those used to more conventional systems.


The DynaMaxx sums up what we have come to expect from SPL of late — a combination of cleverly applied technology and deceptively flexible features, combined with an easy‑to‑use interface.


£586.32 including VAT.