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Flux Plug-ins

Dynamics & EQ Processors For Mac OS & Windows By Mike Thornton
Published May 2008

Flux claim that their plug–ins combine simplicity and sophistication, thanks to their unusual interface design and novel controls.

I came across French plug–in developers Flux almost simultaneously via two different routes. The first was finding their excellent free plug–in BitterSweet (introduced in my feature on free utilities and plug–ins for Pro Tools in the February 2008 issue: The second was when I was hunting for a de–compression plug–in — no, not a cure for the bends from resurfacing too quickly after diving, but a plug–in that could reverse the effects of over–compressed audio.

One of the big selling points of all the plug–ins made by Flux Sound & Picture Development, to give them their full name, is a slider that allows users to morph between presets, giving "ultra–fast operation even for plug–ins including many parameters". The range currently includes several dynamics processors and an EQ, all available as RTAS and AudioSuite plug–ins for use in Pro Tools, and in VST and Audio Units formats for use in other hosts. Both Mac and Windows platforms are supported, and there are also non–native versions that run on the Pyramix DSP hardware.Solera combines four separate dynamics processors into one plug–in.Solera combines four separate dynamics processors into one plug–in.


The Solera meters are unlabelled, and for some reason are referenced to –16dBfs.The Solera meters are unlabelled, and for some reason are referenced to –16dBfs.Solera, the flagship of the Flux plug–in range, represents a different approach to dynamics processing, far removed from the traditional 'three knob' dynamics processor. Flux say they have primarily designed it for mastering and remastering applications. Solera has four dynamics processors built into the one interface — a compressor, expander, ce–compressor and de–expander — as well as side–chain EQ and M/S processing. At first glance, the interface presents a lot to take in, and I found a number of things unclear, so I wasn't confident I knew what was going on all the time. My first problem is that none of the metering is labelled, so you have no idea what each of the nine bargraph displays is showing you. A study of the manual sheds some light on this area, but confusion can still arise. The manual says that from left to right we have meters showing:

  • Input level (VU not peak, referenced to –16dBfs. Why? It's not as though –16dBfs is a common reference point, and in the digital world I want all metering to refer to 0dBfs anyway.)
  • Output level.
  • The 'Resultant Envelope' (showing compression, decompression, and clipper activity).
  • Dynamic difference between in and out.
  • Level difference between in and out.

That is five items, but there are seven vertical bargraphs, so you might expect that the first two would be input left and right and the next pair for output left and right, with the last three covering Resultant, Dynamic difference and Level difference, but the screen suggests that this can't be the case, as it displays a massive level difference between the two stereo channels. Only after further experimentation did it become clear that these were displaying the Mid and Sides levels as I was using Solera in M/S mode.

Then there are the two horizontal meters under the seven vertical ones. The manual describes the orange one as a 'dynamic meter', and the blue one as representing the release variation in auto–release and advanced modes, with fast release on the left through to slow release on the right. What does 'dynamic meter' mean? It looks very pretty in action, but what is it trying to tell me? The manual sheds no more light on this. Some labelling of the meters would be very helpful and save confusion and delay in trying to interpret what is going on.

Under the main display section are the controls for each of the four dynamic processors that go to make up Solera. These are relatively conventional in their format, and the dynamic curve display shows how your adjustments will change the response. The side–chain EQ section too is relatively conventional. Each of the three bands can be either low cut, low shelf, high cut, high shelf or peaking, making it possible to set up complex side–chain equalisation to handle a variety of challenges.

On the left–hand side of the plug–in are four rotary controls. The top two adjust Input and Output Level, with a surprising range of adjustment of +48 to –48dB! As a result of this wide range I expected that the sensitivity of these parameters to be compromised, but Flux have carefully designed their control law so that problem doesn't seem to arise.

Share The Love

Below the Input and Output knobs are two controls unique to Flux dynamic plug–ins, Angel's Share and Hysteresis. Flux claim that Angel's Share "literally opens the sound, increases the dynamic impression and keeps some crest by adjusting in real time the ratio of every dynamic processing section regarding both their current settings about ratio and the signal content (mainly dynamic range)". They advise that the best way to understand this control is to try it out with either a full mixed drum kit or a complete mix with punchy drums, and to set Solera to get near to a pumping sound. As they predicted I did get the sense of a more open, less compressed sound with the Angel's Share control in action.

Hysteresis allows compression and de–compression to be triggered by dynamic variations in the input signal rather than by its absolute level, as in a conventional compressor. This setting doesn't affect the expander and the de–expander processing. In essence it stops the amount of compression applied being level–dependent, making the threshold control redundant. With a conventional compressor, once the audio goes below the threshold, the compressor stops working and so it isn't possible to apply compression to the low–level content without hammering the loud sections. But Hysteresis makes it possible to compress both quiet and loud sounds alike.

I found it quite hard to get my head round this, so I followed the guidance given in the manual. Sure enough when the threshold was up at maximum and no compression was taking place, the content started to be compressed again once I wound in the Hysteresis, and remained no matter how much I reduced the input level. Of course it is possible to have both, and so the best idea is to adjust the compressor in conventional mode to sit on the loud stuff nicely, then add Hysteresis in to taste so there is some non–level–dependent compression taking place as well. This has got to be an excellent tool for those vocal tracks where the singer has an enormous dynamic range.

Tucked away on the left–hand side of the dynamic curve display is a Dry Mix control. This enables you to mix in some unprocessed input signal with the processed signal. This technique is often called 'parallel compression' and is very useful in both compressing drum subgroups and classical music. If this is a new technique to you, take a trip round the Internet putting 'parallel compression' into your preferred search engine.

Sister Morphing

Another unusual feature in the Flux plug–ins is the ability to morph between two completely different presets. At first I wasn't convinced how useful this would be, but after extensive experimentation with Solera, I came to appreciate this feature.

The Morph control can be automated, but only at the expense of not being able to automate any other parameters — the Automation button lets you decide which you prefer. To enable two presets to be loaded into the one plug–in, Flux have had to add their own preset library in addition to the standard Pro Tools system, and presets saved in one library don't appear in the other, although it is possible to import them across from one to the other. It is a shame that the preset library system couldn't be fully integrated.

Down in the bottom right–hand corner is a button labelled Clipper. According to the manual, this activates a brickwall limiter limiting audio to –0.01dBfs, but there is no indication where in the signal chain this brickwall limiter is. It doesn't appear to be the last thing in the chain, as it is possible even with the Clipper in circuit to output signal from the plug–in in excess of 0dBfs. In addition, it took me quite a while to work out how to see when the Clipper was working. Eventually, I established that the top segment of the Resultant envelope display lights up when limiting takes place. However, this whole process showed up another shortcoming that there are no peak level indicators anywhere in the plug–in. I would expect some indication somewhere in the plug–in to show that the signal level has exceeded maximum — the input and output level meters are no help as they are VU meters and so don't show peak level activity.

I tried Solera on the demo material I used in my Limiter Shootout articles in May 2006 ( and August 2006 ( and found it possible to get good results on all the various test files, but it took me along time to get there. Some of that may be attributable to me getting used to Solera's interface, but good results didn't land easily. As a rule, I was unable to get enormous loudness improvements although the sound quality was generally very good — but then I always had to err on the side of caution, as I couldn't be sure about peaks going over.

Overall, Solera is a comprehensive dynamics processor that is capable of excellent results with a number of unique features that make it stand out from the crowd. However, the lack of clear, understandable metering makes it very difficult to get quick and effective results with it, and so for me, Flux have not succeeded in their stated goal of combining "simplicity and sophistication" with this plug–in.

The Pure Range

The Pure range comprises individual dynamics plug–ins based on the elements of Solera.The Pure range comprises individual dynamics plug–ins based on the elements of Solera.The individual components of Solera are available as separate plug–ins within Flux's Pure range. Pure Compressor is a conventional compressor plug–in with Flux's unique Angel's Share and Hysteresis controls added. Having thought that the Hysteresis control would be an excellent tool for handling vocalists with a wide dynamic range, I dropped an instance of Flux's Pure Compressor onto a suitable track and all I can say is that it is amazing. The low–level compression from the Hysteresis mode gives the quiet sections density so that they sit well in the mix, and with around 50 percent Hysteresis dialled in, the level–dependent conventional compressor takes over and manages the loud sections well too. Pure Compressor is an excellent, natural–sounding compressor, obviously compressing but doing it almost invisibly, which has to be the aim of any good compressor. I also tried it on a bass guitar track and a great sound just fell into my ears. It was so easy to set up.

My only criticism applies to the graphical interface: as you can see, the plug–in is narrower than the Pro Tools plug–in 'header' section, so losing screen space on each side of the plug–in window, and for me the Dynamics Curve display is too small to be really useful. I would suggest changing this plug–in window layout from portrait to landscape and increasing the size of the dynamic curve section.

Pure DCompressor is designed for upward expansion, where the dynamic range of signal above a  threshold value is increased.Pure DCompressor is designed for upward expansion, where the dynamic range of signal above a threshold value is increased.Pure DCompressor is designed to help restore the original dynamic of a sound that has been over–compressed, and is one of the reasons I came across these plug–ins. A while back I was asked to improve a covert recording that had been made of two people talking. The problem was that the wanted audio was almost at the same level as the background atmosphere, as it was recorded in a cafe with loads of chatter and noise. At the time I didn't have a good de–compressor, by which I mean a dynamics unit that is the opposite of a compressor in that it increases the dynamic range of everything above the threshold.

So I pulled up the Session from my backup drives and dropped DCompressor onto the track to see if it would help. Sure enough, with some careful adjustment of the Threshold, Ratio and Range controls, I was able to significantly improve the intelligibility of the audio. However, I became aware that I could probably improve it even more if I applied some downwards expansion as well, so I swapped DCompressor for Solera, set up the DCompression section as I had it on the DCompressor plug–in, and then added some downwards expansion using the Expander section. That did indeed help to push down the background atmosphere and further improve the intelligibility. I could have used the Expander plug–in as a separate plug–in in addition to DCompressor but I preferred having both in one window, as it mad it easier to manage the interaction between them.

Overall, this has got to be the best decompression plug–in I have found. Because it is designed to work exactly like a compressor except in reverse, it is excellent not only for forensic work, but also for breathing some life into over–processed audio.

Pure Expander is a  true downward expander.Pure Expander is a true downward expander.The expander section is also available as a plug–in in its own right. Pure Expander is designed to produce a wide range of expansion processes from subtle expansion to a hard noise gate. Its interface continues the form and layout of the other dynamic processors in the Pure range, with the same drawbacks. I was very quickly able to clean up some spillage issues on a live recording session using this plug–in as a soft downward expander. I also tried in on a drum kit, and again, was very quickly able to tidy up spillage on a kit.

Pure DExpander is a  low–level compressor which reduces the dynamic range of signals below a  threshold value.Pure DExpander is a low–level compressor which reduces the dynamic range of signals below a threshold value.Pure DExpander, meanwhile, is designed to enhance the low–level information in your signal and so make your sound more 'compact'. For me this plug–in is much more useful as a low–level compressor than as a tool to undo the excesses of low–level expansion, although of course it can do that. There are times when I want to be able to reduce the dynamic range of low–level content whilst leaving the loud elements more or less untouched. I tried this plug–in on some vocal tracks and was very quickly able to increase the density of the softer vocals so that they sat more firmly in the mix and then use a conventional compressor to handle the louder sections. The only issue I encountered was that this treatment tended to emphasis the breaths.

Reaching The Limits

Designed for mastering applications, Pure Limited is a  single–band brick–wall limiter.Designed for mastering applications, Pure Limited is a single–band brick–wall limiter.Finally, Pure Limiter has been designed to be the very last stage of your audio processing chain. Flux claim it uses their exclusive technologies to generate a release envelope that adds no artifacts to the processed sound. An automatic mode allows quick setup, but Manual and Advanced modes allow you take greater control of the processing.

Pure Limiter features two display modes. When Mode A is engaged, both original and limited waveforms are displayed. Mode B displays the limited waveform, the limiter action and the histogram of the Release value, which they suggest is especially useful when running in Advanced mode.

I tried this plug–in on a selection of the test files from the Limiter Shootouts we have had in the May and August 2006 issues of SOS. It was a dream to use, with the Auto recovery setting being very effective for most of the test files. The only test track it didn't handle very well was the rock opera file. It produced a duller sound than most of the other single–band limiters, and I couldn't work out why. I have already successfully used this Pure Limiter when mastering a client's solo flute album, where it came across as incredibly transparent.

Like the others, Pure Limiter is a transparent and easy to use plug–in, and unlike some, has a well designed graphical interface, although I am still not sure that either of the display modes actually show anything useful that isn't covered by the rest of the plug–in. It is a shame that none of the individual plug–ins have a side–chain EQ like the full Solera does, though. Also, none of them have an external key input, which in my opinion would be an excellent addition to the feature list.


Epure is an equaliser with a  number of neat touches. The grey shaded area represents the overall response, with the coloured lines showing how each band contributes.Epure is an equaliser with a number of neat touches. The grey shaded area represents the overall response, with the coloured lines showing how each band contributes.Epure is a five–band EQ plug–in that at first glance appears very similar to many others. However, hidden away are a number of features that lift it out of the sea of EQs that are out there. For one thing, it has the common feature from all the Flux plug–ins for morphing between presets, which I found especially useful on an equaliser.

Flux Plug–insThe vertical scale of the Epure frequency graph changes dynamically depending on how much boost or cut you're applying.The vertical scale of the Epure frequency graph changes dynamically depending on how much boost or cut you're applying.Then there is a stunning piece of user interface design in that the display auto ranges as you adjust the EQ cut and boost. In the first screen, right, I have boosted a low–frequency peak EQ by just under 6dB. In the second, I have increased that to just over 6dB and as you can see, the display has changed its resolution. I have seen this feature on EQ plug–ins on other platforms but to see it implemented on a Pro Tools plug–in is brilliant. It makes subtle adjustments so much easier, as you can really see what you are doing. I also like the way that each section has its own colour–coded line showing what effect it is having and then the shaded area shows the overall response: so simple and yet so effective.

Epure can be used on multi–channel tracks, and allows you to link any or all of the channels. Epure can be used on multi–channel tracks, and allows you to link any or all of the channels. A small button just below the Master Gain control in the bottom right–hand corner of the plug–in hides another great piece of user interface design. Normally, a multi–channel EQ gives you the choice to link all channels or none. With Epure, however, Flux have enabled you to choose which channels will be grouped to which other channels. When you click on this little button, the graphical display section of the plug–in window changes to display a signal routing matrix. The default routing for a stereo instance of this plug–in has input 1 routed to output 1 and input 2 routed to output 2, with the controls grouped together as group 1. Alternatively, though, you can select M/S encoding on the input and M/S decoding on the output and split the controls of the two channels to groups 1 and 2 in order to EQ the Mid (sum) signal differently from the Sides (difference). But it is possible to take this much further, especially on 5.1 tracks, where you could have one set of controls grouped together for the front channels with a different group controlling the rear channels.

All these almost–hidden features make Epure an incredibly powerful and versatile EQ plug–in, and it sounds very good too. This is my favourite Flux plug–in and stands a very good chance in becoming my EQ of choice.


  • Dynamics processors offer a very different approach compared with traditional designs.
  • Hysteresis, Angel's Share and Morphing controls are effective and unusual features with noticeable sonic benefits.
  • Epure is an excellent EQ plug–in.


  • Graphical user interface is not well through on most of the plug–ins, especially Solera.
  • The referencing to –16dBfs on the displays is very confusing.
  • Flux's own preset system doesn't share libraries with the default Pro Tools system.


Flux have taken a different approach and produced very useful set of plug–ins with a number of unique features that can handle a wide range of dynamics duties well and their EQ plug–in design is outstanding. It is a shame some of them have been let down by some poor user–interface design.


Solera & Epure 478.40 Euros each; other plug–ins 119.60 Euros each. Prices include VAT.