Ideal Of Beauty

by Fritz Fey
Studio Magazin (Germany) – January 2007

Most studio gear in the market would win a design price only in exceptional cases. The plain, sometimes almost ‘amateurish’ appearance is maybe supposed to suggest the impression to the user that it is all about plain tools for working, with form exclusively following function. According to my experiences this is not always in accordance with the facts, as the creators of our mostly beloved equipment are engineers with a focus on technical objectives. In cases like these, the user can yet be thankful if the process of creating the user interface has taken ergonomic considerations into account at all. The aesthetics of radio knobs of the sixties also is not everyone’s favor, but at least their surface feel is fine. Well, with the alpha compressor by elysia this chapter of gear history has to be written anew, as a unit with such beautiful aesthetics, revealing its capacities straight to the eye of the beholder, is a rare thing.

But all this beauty is not only intended to caress our eyes – ergonomics, lucidity and a good and precise feel of the controllers merge fluently. One notices that somebody really aimed at making everything completely right. Even if some people disavow it, an outstanding characteristic of our industry are the people that – even it sometimes leads to self-abandonment – follow their intention, because they have that certain idea in their head that they put into reality with great commitment and enthusiasm. This is how it started decades ago, and this is how history is repeating until this very day. For me this is one of the fundamental reasons to look upon mass produced gear for everyone with certain skepticism and even resentment, because it scarcely represents the soul and creativity of the inventor.

Reflections like these might not play an important role in the rough everyday life of assembly line media production, but the goals are different there, too. However, the true art of sound lives on outstanding ideas, even when they are more and more often looked upon as luxury goods that are pushed aside by economic considerations. But we do not want to mind that in this article, because it is all about exceptional quality awareness, sound composition in service of music and enjoying the art of realizing musical expression in a technically perfect way.

An unimposing hand drawn sketch was the beginning of a dynamics processor that was going to be so different from what is commonly called a compressor, also regarding its outer appearance. The initiators of the company elysia which was founded on the basis of this product idea are Ruben Tilgner and Dominik Klaßen. Among other things, Ruben Tilgner is the developer of the ingenious SPL Transient Designer that has attracted many users all over the world because of the general product idea and its philosophy of easy operation. The Transient Designer has established an essential form of envelope shaping that has been adapted by a discernable number of software engineers for their plug-ins.

I would like to quote a text passage from the elysia website: “The independence of our enterprise enables us to follow extreme paths in our work. We like to try out a lot and are only satisfied when there is nothing left to improve. Besides, we never discard unconventional ideas airily – we test all of them and then form our opinion. Our most important rule is that the ear always comes first, but we also like to please the eye by reflecting the inner values of our devices on the outside with an exclusive design.” (Quotation ends). But this shall be enough of glorious introduction – let’s have a look at the facts!

Overview
The alpha compressor is an analog stereo compressor for highest requirements built with hand selected components. On top of the classic functions it surprises by a couple of special features like the integrated M/S matrix that allows processing mid and side signals separately form each other, a blend controller for the direct and the compressed signal (commonly known as parallel compression), as well as the niveau filter that offers easy but very interesting sonic changes which are independent from the dynamics stage. Furthermore, there are functions like the sidechain filter that allows frequency-dependent compression or the switchable automatic control of the attack and release parameters which only reacts to fast transients and gives priority to the value set manually for the rest of the time.

Each of both channels is equipped with an additional transformer which can be switched in for sound shaping reasons – not a very explicit effect, but a delicate effect for mastering specialists. The option to switch between feedback and feed forward operation results in entirely different control characteristics of the device, offering the choice between elegant and inaudible or brutal and intentionally rough changes of the program dynamics. Finally there is a Soft Clip limiter that extensively protects the following signal chain from clipping. This limiter approximately behaves like the saturation of analog tape machines which are known to round signal peaks and therefore have become a popular sound shaping tool that has more or less successfully been emulated by lots of analog and digital circuits in the meantime. Setting this limiter has to be done with certain care and should only aim at fast signal peaks, otherwise unwanted and certainly audible distortion will occur.

A little bit technology…
Having a look at the inner values of a piece of equipment is an important part of any gear review, even if the larger part of the readers will fly over these passages with enhanced reading speed. One is tempted to say: In the beginning was the power supply, because adequate and clean power is the essential thing for any analog equipment with high sound pressure level capability. The alpha compressor supplies all active stages with ample amounts of current, which is especially important when fast signal impulses occur. For this reason the power supply provides sufficient capacities by using high end electrolytic capacitors. On top of that, many places of the circuitry feature additional MKP capacitors to even extend the generous supply. The voltage of +/-30 volt is regulated by discrete circuits that noticeable work below the background noise of the whole unit. If you are interested in this detail and would like to learn more about it, you can check out the elysia website for further information.

To my mind, another point is even more noteworthy: Beside other delicacies like a pure class-A design and discreet amplifier stages my attention was drawn to the abbreviation PCA which stands for ‘Passive Current Attenuator’. The most important part of a compressor is without any doubt its gain reduction element which is alternatively based in FETs, light-sensitive resistors (opto compressors) or VCAs. True to the motto ‘If you want something done right’ the manufacturer has developed a custom component: a discretely built element (PCA) that converts the incoming audio signal into a current which can then be reduced by voltage. The core of this element is based on 16 transistors which are kept at a constant temperature by a dedicated heating system.

The PCA is a passive component without amplifier and thus only reduces signals. Not until a following amplifier stage the current is transferred into voltage again. All control processes have been deliberately optimized for an unobtrusive, careful approach to the signal. If one really wants to enforce more drastic control processes, the feed forward mode comes into operation. The benefits of the PCA are its wide bandwidth and its extremely fast speed of only a few micro seconds. elysia has tuned the PCA in a special way so that it produces a certain amount of harmonic distortion in order to give the alpha compressor its special sonic characteristics. I’ll come back to this point later.

Operation and Functions
Once one has recovered from the adoringly marveling view of the front panel, the clear and concise layout of the controls becomes obvious at once. All controllers have been equipped with a glass lens head emitting blue light, and the indicator also emits light and casts a small, but well visible shadow into the scale ring, thus all controller positions can be read well. All push buttons are illuminated by white LEDs when their corresponding function is activated. The only push button with blue light is the bypass or ‘Active’ switch. Carrying the design element to the extremes, both the controllers and the push buttons have an individual adjuster for the light intensity on the back panel which is also illuminated in the corresponding color. This adorable gimmick accounts for the sake of ‘enthusiasm’ or ‘fun.

The gain reduction meters are placed as crescents of red LEDs to the left and the right of the central illuminated elysia logo and stay active even in bypass mode (hardwire bypass). Two yellow LEDs above of the meters indicate the operation of the Soft-Clip limiters. Three rows of detent controllers and push buttons indicate the three functionality stages for each of the two identical channels. The top row holds the parameters for setting the compressor, the mid row is for the filter functions, and the lower row is all about level adjustments. The push buttons for M/S operation, bypass and stereo link are placed in the middle of the unit, right beneath the elysia logo.

For a start, the compressor offers classic parameters like threshold, attack, release and ratio. The scale for the attack shows values from 10 microseconds to 150 milliseconds and the release can be set from 60 milliseconds to 1.8 seconds. The ratio parameter reaches from 1:1.1 to 1:2,4, but it rises in feed forward mode. This mode can be activated by the corresponding switch which can also be found in the compression section. So far, that’s nothing new, but now two further push buttons come into play, as both the attack and the release controller are complemented by a feature called “Auto Fast”. This function causes an automatic shortening of the time constants on incoming signal peaks. This means that the compressor will react very fast for a short moment of time and then return to the (slower) value that was set with the corresponding controller.

This is a special case of (semi)automatic control of the time constants that we have rarely or never seen on other units which also offer an automatic adjustment of the time constants. The filter section is separated into two sections: On the one hand, there is the niveau filter that follows the compressor section and which therefore does not have any influence on the control mode, but is responsible for broadband changes of the program sound. On the other hand, a sidechain filter increases or decreases the compressor’s reaction on high or low frequencies by acting as high pass or low pass filter respectively.

The niveau filter is a traditional circuit from the good old times that makes it possible to tilt the frequency response around a tunable center frequency like a pair of scales. When the gain controller is turned fully clockwise, the frequency range which figuratively lies right of the center frequency is boosted by 3 dB, while at the same time the area left of the inflection point is cut by 5 dB. When the controller is turned fully counter-clockwise, everything behaves just the other way round. The corresponding center frequency can be switched between 20 Hz to 2 kHz and 2 kHz to 20 kHz with the push of a button. A filter like this can be used to change tendencies of timbre in a very subtle yet effective way, especially when the M/S matrix is activated.

The lower controller row marks the level section of each channel, featuring a mix controller for the direct and the compressed signal (instant parallel compression), a gain controller and another potentiometer for the threshold of the Soft Clip limiter. Also very interesting are the ‘Direct’ and ‘Compressed’ push buttons. If only one of these is pushed, only the corresponding material (original or processed signal) is audible. If both are pushed, however, the mix controller with its blend function becomes active. This makes it possible to not only to listen to the direct or the compressed signal apart from each other, but also to A/B the actual mix status without having to change the controller setting. Finally, the level section also offers the ‘Transformer’ push button which can be engaged in order to add that typical ‘iron’ to the sound.

An absolutely distinctive feature is the integrated M/S matrix that splits the stereo signal into a mid and a side channel and decodes them back to stereo again after processing. Everyone who has ever worked with M/S coded signals on compressors or equalizers knows how valuable this function is when processing stereo signals. The fact that the channels can also be operated in unlinked mode invites to process them separately from each other, for example by applying a massive amount of compression to the mono information (M=L+R) without touching the side information (S=L-R) at all. More on this follows in the “Practice and Listening” section.

Measurements
In our measurement analysis, the circuit technology the alpha compressor is based on showed a constantly high quality level that can live up to its outer appearance by all means. The maximum input and output level in normal stereo mode corresponded to the manufacturer’s specification of about +28dBu, at which the harmonic distortion of both the input and the output for this value lay at approximately 0.5 percent. It is striking that the harmonic distortion raises continuously starting from circa 0.1 percent at +23 dBu up to the maximum level, thus it is not as abrupt as most semiconductor circuits. Due to its circuit topology, the maximum level of +23 dB in M/S mode is 5 dB lower, which should still be excellent in practical use.

Diagram 1 shows the extremely linear level and phase versus frequency response of the compressor, which shows a slightly untypical characteristic far above the auditory threshold with a noticeable raise in level, though. The manufacturer explains that a self resonance of the input transformer is responsible for this phenomenon, which has been accepted for the benefit of phase response and transient projection. In practical use, this phenomenon does not play a role at all. The output noise showed the good value of -86.1 dBu RMS effectively unweighted (22 Hz to 22 kHz). Considering the maximum output level this results in a dynamic range of not less than 114dB. A quasi peak measurement with CCIR filter showed -75.4 dBu of noise.

Diagram 2 shows the FFT spectrum at the output with exemplary characteristics. The common mode rejection of the inputs (Diagram 3) reached approximately -86 dBr at 1 kHz which reduced to -63 dBr at 15 kHz. The crosstalk between both channels at -67 dBr (largely depending on the measured frequency) couldn’t convince us fully. However, this can be attributed to the integration of the M/S matrix which increases crosstalk by design. But a problem can only occur when both channels process signals that are very different from each other and that have frequency-response curves which are unfavorable concerning crosstalk.

Diagram 4 shows how the very flexible niveau filter works at settings left to the 12 o’clock position. Of course, settings right to this position result in the same characteristic but with an opposite course. Diagrams 5 and 7 deal with the dynamic attributes of the compressor: diagram 5 shows the effectiveness of the ratio parameter in feedback mode, in which the characteristic curves of a typical soft knee compressor with variable compression ratio become evident. Diagram 6 shows the correspondent characteristic curves of the compressor’s feed forward mode – it is easy to see that things become much more intense here.

In this mode the alpha compressor produces drastic control processes that even culminate in over-compression with negative ratios. Diagram 7 shows the characteristic of the switchable Soft Clip limiter at different threshold settings. Finally, diagram 8 shows that the alpha compressor produces noteworthy harmonic distortion at higher levels – and that is fully intended, as the manufacturer assures…

Practice and listening
The basics section of the excellently written and illustrated user manual starts with the words “no fear”, presumably with the intention of eliminating potential user stoppages that might occur from facing the variety of functions offered. Folks – whoever is expending nearly 8.000 Euro on a compressor can be confidently classified as a fearless person. So no fear, dear elysians, your baby will certainly never fall into unpracticed hands deliberately. Of course, as a declared friend of premium analog technology I have spent quite some hours with the alpha in the meantime, but still I always pay attention to the impressions of the very first minutes: How does a piece of equipment feel? How fast do I understand its operational concept? How soon do I hear a result? How is the first sonic impression?

The alpha compressor could convince me at once in this matter: a very superior thing. Because of the detents of the controllers, matching the channels can be done fast; the gain reduction meter harmonizes very well with the audible result; the compressor does not cause any sudden trouble. In short: I feel home at once. The manufacturer has paid special attention to create an absolutely symmetrical channel layout with low component tolerances. A good decision, as the alpha sounds very open and ‘right’ straight from the beginning. The processing is downright ‘elegant’ and ‘smooth’, so that even on strong engagements the original dynamics is not bent in a counterproductive way. It’s a sure thing that one wants to listen to a compressor with an M/S matrix in this mode at once. We have gained lots of experience with this kind of signal processing in our own studio thanks to the M/S compressor section of our TC System 6000, and we definitely do not want to do without this function again, and this is true of production as well as of mastering applications as well.

Someone who experiences these potentials for the first time will encounter a completely new world of processing that reaches far beyond mere changes of dynamics. A slight raise of level in the S channel will already result in broadening the stereo basis which cannot be achieved with any other gear offhand. Processing the M and the S channel separately from each other allows an independent access to the mono information. This makes it possible to give soloists who are likely to be found in the stereo middle a stronger embedding, or to create a more dense rhythmical arrangement by applying stronger compression without touching the dynamics of the stereo or spatial information. A stronger compression of the side channel shifts the stereo information in the foreground so that it becomes more articulate and gains in width and general profile at the same time.

Adding the side chain filter aims at even more selective operations, for example by making the compressor more sensitive towards certain frequency areas in order to add an ex post de-esser to the vocals or to just compress the low frequency area. It is a completely different style of working that opens up new dimensions of musical changes to mastering engineers and production studios alike. But the M/S mode also implies very important options for the integrated niveau filter. An easy shift of balance around a selectable center frequency can give the mix a different coloration without changing the important program contents of the mono channel. A standard stereo compressor does not stand a chance here. I would like to give your own fantasy room for creating further ideas, as the functionalities of M/S compression and M/S equalization would be worth an article of their own.

We have specifically chosen some of the features of the alpha compressor in order to have a closer look at their usefulness. This includes the ‘Auto Fast’ parameter for attack and release which makes the unit ‘intelligent’ in a special kind of way. The reaction of the compressor to fast transients works with a high degree of reliability indeed. Thus playing with two active time constants (the automatic and the manual) leads to faster results, but also to an overall more ‘correct’ control behavior. As to my impression, the intensity of the ‘Auto Fast’ function depends on the specific settings of the threshold and the ratio, one definitely has to keep and eye (and ear) on the rounding effect on the transients. If it is important to keep the response behavior of the transients as close to the original as possible, setting a longer attack time manually or employing the mix controller can sometimes be the better solution.

The alpha compressor can handle a rich number of different dynamics processing tasks, and it also offers excellent services when used as a track or buss compressor. Although the mix controller seems to live an unimposing life on the front plate at the first glance, it turns out to be an important function at second sight which could otherwise only be realized with additional routing efforts in a mixing desk or DAW surrounding. Blending between the original and the compressed signal is especially effective if the envelope structure of the compressed signal shows distinct differences to the original. If you use the compressor to drive a drum track ‘against the wall’ without mercy and then mix the result to the original, for example, you can create very exciting spatial effects that give a complete new definition to the character of the recording room or to the drums as resonant bodies without affecting the original dynamics.

Among experienced engineers this method is known as parallel compression, and with the alpha compressor you can control this feature in no time at all with just one controller. Finally, I’d like to mention some very pragmatic comments about this unit. In a mastering studio, it assures 100 % reliable repeat/recall capability of all settings and a guaranteed perfect symmetry of both channels by the precise balance of the detent controllers. The illuminated controllers are certainly a gimmick and might even be counterproductive in shaded ambient light, because they could outshine the print on the front plate in the worst case and reduce its readability as a consequence. But whoever gets to know the unit a little better will want to see less and listen more anyway.

Still, this optical effort costs money that maybe not everybody wants to pay willingly. But I really do not want to start a discussion on whether a version of the unit with the same technical functionality but without the elaborate illumination would address a broader public, as it would just not be fair to call a synthesis of the arts like the alpha compressor into question. The unit is a complete winner and holds all promises concerning technical realization, workmanship, sound, ergonomics and creativity that its incredibly attractive looks anticipate.

Conclusion
The debut product of the still young company elysia can be called an instant hit with all confidence. The alpha compressor is an exceptional development that cannot be found in the world market a second time. The integrated M/S matrix plays an important part, of course, and also the details of the sophisticated concept and the elaborate technology push the unit into the top flight of the market easily. Its immense flexibility does not show at first sight, but this compressor has lots of different faces: the elegance of a finishing mastering application, the powerful grip of a track or buss compressor, the gentleness of processing sum signals and the ingenious behavior of an effect compressor for special tasks.

The alpha compressor’s build quality is very sophisticated and high class. No expenses have been spared and the design is simply one of a kind. The price is definitely not nothing, but it is justified in every respect. You can feel it when you touch the knobs, you can hear it when your work with the alpha and you can see it when you come into your studio – a treat in every aspect. Thank you, dear elysians, this is the definition of finest analog technology today and we are looking forward to your next product developments!