Stereo Compressor With Special Functions

by Hannes Bieger
Sound & Recording (Germany) – February 2008

Not so long ago, German manufacturer elysia caused a sensation with a true compression bolide: in no time at all, the alpha compressor became one of the favorite tools of the international mastering engineer community. Now here comes the second coup…

The innovative power of the young company elysia certainly has its background: Chief engineer Ruben Tilgner is an old hand who has developed the bestsellers GainStation and MixDream for SPL. And with the Transient Designer he proved very early that he not only understands how to build a good signal path, but also knows how to develop notedly innovative concepts and make them hit the shelves. elysia remains true to this philosophy on an extremely uncompromising level: with its almost 5-digit price tag the alpha compressor flagship is a mastering bolide that neither lacks functional range nor technical realization. Both the inside and the outside of this unit are downright exquisite – and even if some vintage fundamentalists might start to cry in the face of such a concept, one thing is for sure: A well thought-out unit like this cannot be found in the market a second time.

Now the “younger brother”, the mpressor, gets ready to hit the scene from a different angle. Its parentage is obvious, as a lot of the alpha compressor’s design elements can also be found on the mpressor. But, being the youngest scion, it needs to go its own ways in order to make itself heard. So it's not just another high end unit, as it offers special functions currently not to be found anywhere else – and especially not in this combination. Also very nice: the control elements nevertheless stay pleasingly straight forward.

The concept of the mpressor
With its feed forward control, class-A audio paths, fully discrete design (even the power supply and the detector path) and without transformers in the audio path, the mpressor speaks a very modern “language”: it basically aims at transparence and dynamics and not so much at typical vintage saturation effects – but with certain settings it can be overdriven as well. The detector element is a so called Transconductance Amplifier (TCA) which consists of single transistors kept at a distinct operation temperature by a heated copper element. Similar to the oscillators of the Minimoog, this technique helps to reduce environmental influences on the sound character of the unit. One of its special qualities is that the noise floor does not rise on strong compression and make-up gain rates. This makes even drastic processing without LoFi artifacts possible.

The mpressor is equipped with the typical basic functions of a compressor. All of its parameters can be controlled with individual pots. On top of this, the mpressor not only offers the possibility to feed an external detector signal into its sidechain, but it also has a couple of quite uncommon features. Let us start with the Auto Fast function: It helps to cope with a problem that almost every compressor has which has become even more severe in our digital age without tape machines helping to tame signal peaks.

If you process a signal with a lot of transients and low end (e.g. a slapped bass or a drum subgroup), the difficulty to choose an adequate attack time of the compressor will pop up. If a very short time is set, the transients will be “caught”, but in most of the cases they will be so short that the bass frequencies will start to distort – because the compressor is triggered by every single oscillation anew. If you choose to avoid this problem by setting a longer attack time, the transients will not be detected by the compressor, and the use of the unit even becomes counterproductive: The compressor starts to work only after the transients have already passed, and this makes the dynamic range even larger and the unit functions as an expander. “Auto Fast” is the solution: It catches short and loud signal peaks safely, even when longer attack settings are chosen in favor of the bass frequencies.

“Anti Log” kind of turns the characteristic of the compressor during the release phase upside down. A compressor usually works in linear or logarhithmic mode, whereas the mpressor reverses this process: At the beginning of the compression phase the release time stays longer and it becomes faster not before the input level drops significantly – drastic and “effective” results occur, and the elysia mpressor “grooves” completely different then.

The negative ratio values follow an equally drastic route: The louder the input signal is, the quieter the output signal will become. And additional limiter can be activated for the control voltage of the compressor. Thus the maximum amount of gain reduction can be “frozen” at a fixed value – extreme loud parts can keep their dynamics even when a huge amount of compression is applied. Furthermore, the mpressor offers a special equalizer (the so called “Niveau Filter”) that is designed to achieve its maximum effect with a minimum feature set: The complete frequency range is tilted around a selectable center frequency, reminding of a pair of scales. All frequencies below the center are boosted by a certain amount, while everything above is reduced by the same amount – or the other way round. Making a signal overall “darker” or “brighter” can be done with no effort at all.

Last but not least the mpressor has a link function for both of its channels. In order to keep the signal paths short (again, the audiophile approach...), the link only affects the control functions that now can be set with the left channel controllers for both sides. The actual audio signal stages – EQ and gain – still have to be set for each channel individually. The mechanical build is maybe not as exquisite as the alpha compressor's, but don't be fooled by this statement: The manufacturing quality of the mpressor lies considerably above the standards in this price category. Maybe the design of the housing does not fit everybody’s taste, but looking at it from an objective point of view it is beyond any doubt. With its 8 kg of weight (without heavy audio transformers!) the mpressor is built for eternity. Only the power switch is not so practical because it is located on the rear panel of the unit.

In Use
The mpressor covers a large range of sounds. Starting from a neutral and precise base, the unit mostly presents itself in a clear, punchy and defined manner. But you can certainly unleash the beast within! In the field of “normal” settings it recommends itself as a versatile, great sounding all-round compressor that can unfold its virtues on virtually any audio signal. But a complete parallel universe full of special effects that have never been heard from simple compressors before lies only a little twist of the knob away. Especially the negative ratios (which go together with the Anti Log function nicely) open the door to the world of groove effects that sometimes almost seem to derive from a granular engine. These features turn the simplest loops into very surprising and inspiring grooves as you can also hear on our demo CD.

A great feature is the “Auto Fast” mode: it makes the mpressor a true loud-maker, more than many other units can claim to be. And finally, the Niveau Filter is worth mentioning: It copes with sonic corrections in no time at all with great results. It would have been a cool addition if there was the possibility to switch this filter into the detector path of the compressor. A great design achievement is the fact that in face of the extensive functionality and sonic possibilities the unit has relatively few control elements – the musical approach always stays intuitive.

Conclusion
With the mpressor, elysia managed to create a unit that can raise a lot of added value against its not really marginal price. If you are interested in a “modern” all-round compressor that can also turn into a creative sound monster, the mpressor is for you. Not only does it cover the “standards”, but it shines as a loud-maker and convinces with its spectacular sound effects that partly have never been heard before. Only few vintage compressors (e.g. the Dyna-Mite by Valley People) can sound as drastical, and the mpressor goes even further, but without any noise or other LoFi artifacts. In short: It is not cheap, but it is worth its money without question!