A mastering compressor causes sensation!

by Mario Lämmerhirt
Delamar (Germany) – May 2011

Abstract

The elysia alpha compressor is a very sophisticated, fully discrete high end hardware compressor that has been developed by elysia especially for mastering. We all know that the process of “mastering“ has reached out of the studio scene into home recording projects in the meantime, and as a welcome circumstance, the sound quality of corresponding plugins has significantly improved during the recent years. By now, there is a broad range of mastering plugins available, and it only seems natural for elysia to offer their debut plugin in digital form as well.

This feels like a good decision, as the hardware compressor exceeds many budgets, so the price of the alpha plugin brings the option of getting the elysia sound within reach. The alpha compressor plugin is announced as a detailed emulation of the hardware including all the features and its specific sound, now available for the DAW. On top of this, there is an additional reduced version as a mix and tracking compressor included.

'Transparency' in terms of sound, combined with a great 'musical' compression characteristic and its M/S compression capabilities – the alpha compressor seems to be well suited for mastering indeed. But there is also a feed forward mode available that makes the alpha grab if you want it, this much I can reveal already.


Introduction
I my opinion, the hardware units of the German manufacturer elysia stand out because of their special concepts. Among many other things, Ruben Tilgner has designed a particular discrete class-A amplifier with current feedback control in order to meet the high demands of mastering regarding a linear signal processing. The topology is not a FET, Vari-Mu or VCA, but a passive gain reduction cell that works similar to a VCA, but not exactly in the same way.

In terms of sound, the credo of the alpha compressor is maximum transparency (feedback mode). The alpha compressor offers up to four times oversampling, an M/S matrix for compressing mid and side signals separately, a special control characteristic for attack and release (Auto Fast), a sidechain filter for frequency-selective compression, two different styles of compression (Feedback & Feed Forward), a Warm Mode for very subtle coloration effects, the niveau filter (some kind of frequency balance), a Soft Clip limiter and a mix controller for parallel compression.

The additional alpha mix plugin does without the M/S matrix, the niveau filter and the Soft Clip limiter. By the way, just as with the mpressor plugin, it has been the developer team from Brainworx who transferred the hardware into digital code. Of course the alpha is available in all usual formats: VST (2 and 3), AU and RTAS. TDM and VENUE are announced to follow in June 2011. The 14 days trial period for this plugin does not need an iLok, while the full version requires an iLok USB dongle.


Look & Feel

The alpha compressor pops up with a quite large user interface and a decent look to it. One might need a little time for orientation, but it is pretty easy to understand the layout of this compressor, and the right side is an exact copy of the left. The mix plugin does not need much explanation, as here the layout is that of a typical compressor. Let's have a look a the workflow now. In linked stereo mode of the alpha master plugin, the settings you make on the left or the right side are automatically transferred to the other channel. Obviously, separate values can be set for the individual channels in unlinked mode. In this case, the alpha behaves like a dual mono compressor.

The alpha master plugin is only available on stereo tracks, while the alpha mix version works both on mono and stereo tracks. When switched into M/S mode, the controllers on the left side are responsible for the mono/mid signal, while the right side is assigned to the stereo signal. When the M/S matrix is activated in channel link mode, it is still possible to influence the stereo spectrum, because the mix and gain controllers as well as the niveau filters remain unlinked – perfect!

Another benefit in terms of workflow is the possibility to directly compare the processed and unprocessed signals. Right next to the mix controller we find one button each for the direct and the compressed signals. These can be used to solo the direct or the processed signal of one channel, or for muting e.g. the complete side channel when working in M/S mode. The mix controller becomes active once the Direct and Compressed buttons are active at the same time.

Another parallel to the mpressor is that the alpha features the very useful mouse wheel control. The fine tuning is done with Shift + mouse wheel, and you can switch between linear and circular control as well. I got the impression that after only a few hours of usage one gets used to the alpha's workflow easily.


Feedback & Feed Forward

Like mentioned before, it is possible to choose between two different compression styles. The feedback mode offers soft and unobtrusive processing results, while the feed forward mode comes into play when a more characterful kind of compression is wanted. These two compression styles vary in the way the compressor receives its sidechain signal. The feedback mode taps its feed for the sidechain from behind the actual compressor section, while the feed forward mode does what its name suggests. The attack time becomes longer in feed forward mode, and also the ratio values will become much higher, as they allow limiter settings and even negative ratios!

A negative ratio turns the usual concept of a compressor upside down, as the louder a signal gets, the more it will be reduced. And this means that the alpha compressor also has some kind of hidden treasure chest below its surface. In every-day use, the feed forward mode is great for getting things louder and on the drum bus as well. If you unleash it on a sub group or a drum bus this way, the alpha will show that it is not limited to doing gentle things only. Add the mix controller to the scenario and you'll find yourself compressing New York style all the way.

Threshold & Ratio

The threshold of the alpha compressor is based on a soft knee which results in a softer compression compared to a hard knee characteristic curve. This is a result of the compression process already slowly starting before the threshold is actually crossed, followed by a slow rise of the ratio. The ratio itself is dynamic, which means that the value rises when higher amounts of gain reduction are produced. The user manual says that the scaling on the front panel is based on a measured gain reduction of 6 dB. When there is 17 dB of gain reduction going on, the ratio turns up to 4,5 instead of the printed 2,5, and the effect becomes even stronger in feed forward mode. However, as in mastering usually only a few dB of gain reduction are applied, the scaling has been optimized for these lower values consequently.

Auto Fast

The process of compression can produce audible artifacts as an unwanted side effect when a very short attack time is applied to especially dynamic material. The Auto Fast function can help to avoid this, however. With it, one can set a longer general attack value, and the compressor will detect fast dynamic impulses by itself and reduce the attack time automatically for a short moment as a result. After this automatic process, the attack time returns to the value which is set with the corresponding controller. This is a very useful feature for example on a drum bus with high amounts of dynamics, or for the master bus in order to keep the mix vivid. The alpha compressor only gets fast when it is needed, so this is a intelligent semi-automation for the attack (not a fully automatic one that would completely deactivate the attack controller).



The release parameter features a similar feature that finds a fitting release time based on the envelope of the signal. However, there is some kind of interaction going on between attack and release in Auto Fast mode. The longer the attack time is set, the less the influence of the automation will be applied on the release time. The effect will also be smaller on higher release settings.



Sidechain Filter

The combination of SC Freq and SC Gain controllers can be used to choose a frequency area you want the compressor to start or to stop working in. When the SC Gain controller is set to HP, the filter becomes a high pass with 6 dB, turning into a low pass with 6 dB when in LP position. Of course, you can set many values in between these two extremes, so that a part of the covered frequency range will influence the compression process, too. This is really frequency dependent sidechain compression deluxe.



M/S-Matrix

The M/S matrix of the alpha compressor makes it possible to process the mono/mid and the stereo/side information separately from each other. This is sometimes a must when you're aiming at correcting mistakes in a mix, or when the stereo width of a finished mix should be broadened or narrowed ex post. Even DeEssing of vocals in a final mix can become possible under certain circumstances! For me, the M/S matrix and the sidechain filter are the true heart of the alpha compressor.



The possibility of processing mid and side provides new possibilities that a stereo compressor cannot offer. Of course there are external M/S tools available, but for using them you'd need two separate tracks and two instances of the same plugin. The alpha has all this on board for direct access, and this is really great for a mastering compressor.



Niveau Filter

The niveau filter is some kind of swing EQ around a selectable center frequency. It changes the sonic character of a signal, resulting in a 'darker' or 'brighter' sound. The EQ generates a maximum boost of 3 dB and a 5 dB cut at the same time. The center frequency can be shifted x10 with a corresponding switch. In its extreme positions the filter becomes a low cut or a high cut respectively, providing even more sound shaping options. By the way: elysia also offer their niveau filter as another plugin – complete for FREE!



Warm Mode & Soft Clip Limiter

The Warm feature is the only one not to be found on the hardware. With the hardware you have the option to switch an output transformer into the signal path for each channel, acting like a subtle sound coloration generator placed after the mix stage. The alpha compressor plugin replaces this option with the so called Warm mode. This feature is based on a slewrate limiter which has an influence on frequency and impulse response as well as THD. It's a subtle effect, but certainly useful. Especially when combined with the Soft Clip limiter, the lower mids are slightly boosted and the high frequencies are reduced a little bit, which is very pleasant for the ear. The Soft Clip Limiter is not a brickwall, by the way, but a design which is emulating the behavior of analog tape machines. The signal peaks which are not processed by the compression section can be caught and rounded – it's a little bit like driving signal peaks into saturation. And if you really want it loud, you can also use the Soft Clip limiter to get these additional 1-2 dB nicely.



Result

I can recommend the alpha compressor to everyone who is looking to spice up their finished mixes or who is in need of an 'inaudible' dynamic toolbox. The alpha is a very good choice for the final tuning in mastering, especially because of its very transparent sound. You get a very versatile tool for influencing the dynamics of a track without changing its sound at all. If you are looking for something with a vintage-feel, you might miss some more sound coloration here – but there are certainly other tools to achieve this. If a reliable control on dynamics is your goal, the alpha is definitively a go-for processor.



My test period of the alpha mix and master versions has been quite long, so I had the chance to process several projects with them in my studio. I started by mastering a Minimal EP. These tracks were very well balanced already, therefore the mixes just needed a little bit more stereo width and loudness. If it comes to making things louder, I have noticed many times that my finishing tools (especially the limiter) do change the sound character after all. And this is were the alpha compressor holds its first ace. Its transparent sound really surprised me - I was wondering how there could be 6 dB of gain reduction going on without any sonic changes? The Auto Fast function had a good part in the dynamics not loosing its sparkle in this application.



Of course, the sound got more compact, but with a little bit help of the mix controller I was able to find the perfect setting for each single track. Then I added some additional gain to the sides in M/S mode, and I used the sidechain filter to diminish the influence off the bass frequencies on overall compression a little bit. The Soft Clip limiter generated 1,5 - 2 dB of additional headroom, and this was it. Originally I had planned to use more tools to fine tune the Minimal sound tracks in Wavelab, but in the end it was only the alpha compressor which led me to the finish. Chapeau, elysia!



I also finalized a Big Beat production with the alpha, and although there were lots of transients to tame, using two instances of the plugin in a row made my day. I used the one instance to control the transients, and the other one in dual mono mode for a slightly different compression of left and right channel. A double feature, but I could not notice any audible artifacts. On top of this, the alpha really glues things together nicely.



At the moment, the alpha sits in the master channel of a singer/songwriter production where it welds the great amounts of ambience together beautifully. I am also using the mix version on the bass track, where it took the place of the LA2A which originally sat there. C'est la vie – just leave your usual path and you'll find something new! Finally, I would like to mention elysia's quality of support: They are fast, friendly and very competent. Dominik Klaßen guides you through any questions you might have, which is a valuable help. I am sure elysia will release further plugins in the future – and I am looking forward to them, because the elysia sound is great!



Pro

+ Oversampling

+ Very transparent sound

+ M/S matrix

+ Frequency-selective compression

+ Feed forward for stronger compression and sound effects

+ Additional mix plugin

+ Premium support



Con

- Needs an iLok for the full license (additional cost for the dongle)

- Parameters cannot be inserted with the keypad