The Flagship

by Franck Ernould
Réalisason (France) – April 2008

The high-end audio market can sometimes be compared to the luxury market. Some fantastic hand-made machines with stunning designs, amazing features and prices out of the reach of the average audio engineer appear from time to time. Here are two good examples, the alpha compressor and the mpressor by elysia.

A few words about the company first (did you know the Elysée is the place in heaven where heroes and virtuous people find their last rest after they die in the Greek mythology? For Christians, the Elysian Fields are the first outskirt of heaven, they welcome heroes and poets who lived before Christ were born). elysia was created in Nettetal, Germany in 2005 by Ruben Tilgner and Dominik Klaßen.
Dominik is specialized in marketing and communication and worked for companies like Terratec. Ruben is known for his creative work at SPL: He is the mind behind the Gain Station, the MixDream summing mixer, or the Transient Designer, a dynamic envelope shaper with an approach which is still unique today.

To underline his newly acquired independence, Ruben decided to design his own amplifier stage. After considering a bass preamp, followed by an audio processor, he settled for a high-end mastering compressor after the 2005 Frankfurt Musikmesse. He was missing the most difficult element to design, the gain reduction element. After a few trials he decided to go for something completely new, regardless of the price. He drew the front panel of his compressor on a piece of paper: everything was already more or less there…it was presented at the 2006 Musikmesse a year later! ‘It’ is the alpha compressor. It drew a lot of attention at the AES convention in Paris a few months later. Tom Van Den Heuvel, a talented sound engineer, was there, and has since become Mr. elysia in France.

“The alpha compressor is the start, the basis. Its very sophisticated and complex design has contributed to establish the company” says Dominik. “We wanted to show what we stand for in regards of technology and sound: true high end. Which is not easy as this market is obviously small…”. Ruben further justifies this pretty elitist positioning: “I know from my time at SPL that it is difficult to move from an “affordable” brand image to “high end”, regardless of the good quality of the products. It is easier to go downwards than upwards. We won’t live on the alpha for the next five years, but it will contribute to establish ourselves and justify the cheaper products we’ll release in the future”. The first units went to different mastering and recording studios in Europe and the U.S. A few modifications later and the first orders were shipped, shortly after the 2006 San Francisco AES. The units are built in batches of 20.

What makes the alpha compressor different from other high end compressors? It’s a mixture of several interesting matters, among which is its most stunning feature, the M/S matrix, but also its parallel mode, the Auto Fast function, the audio filters for both the signal path and the sidechain. The internal construction is entirely symmetrical in its implementation; you could swear there was a mirror standing in the middle of the unit! But let’s have a closer look at each feature to find out what makes a true racing machine…

Technology
With its 3 U, the alpha compressor weighs no less than 16 kg, boasting 45 potentiometers and 23 switches, illuminated by some blue LEDs (white for the switches, except for the bypass) and 100 watts of maximum power consumption! As you can imagine, it works in class-A mode. A dark metal front plate carries the lettering on a second 12 mm aluminum face plate. One of the most eye-catching gimmicks is the semi-circular LED crowns to display the gain reduction…

The power supply of the alpha compressor wouldn’t look bad in a power amp: +/-30 Volts, huge capacitors, discrete regulating circuits…as for the gain control element: No Opto, no VCA or FET, but something different: a Passive Current Attenuator. This circuit transforms the incoming signal into a current and is then able to reduce this current controlled by voltage. Ruben used no less than 16 transistors maintained at the same temperature by a dedicated device (which should ring the bell of old analogue synths fans…) called T16 Heater. It is worth pointing out that all the circuit components are discrete and chosen specifically for the alpha compressor.

The controllers for each channel are arranged in 3 rows. The first one is the compression section, offering the usual threshold/attack/release and ratio parameters, plus the feed forward and Auto Fast switches; the middle one is dedicated to the filter section, for the signal path and the sidechain; the bottom is used to control levels (make-up gain, mix of original and compressed signal, etc.). A small remark regarding the printed values: The release potentiometer ranges from 50 to 1k8. Being used to reading “Ks” for frequency values on EQs (like displayed on the lower row), we asked ourselves a few metaphysical questions…until we understood we should read “1,800” ms or 1.8 s.

M/S Mode
One of Ruben’s groundbreaking ideas was to implement an M/S matrix for being able to process stereo’s sum and difference on top of normal left/right stereo. This mode can be found in some digital processors, but from what we know, it is its first analogue incarnation (the Manley Vari-Mu can be ordered with an M/S matrix as an option)…This mode revolutionizes the way compression can be addressed.

Let’s imagine a track with voice in the center with a stereo reverb. A traditional compressor would make the reverb “pump” with the voice if lots of compression is applied. This will not happen in M/S mode: The centered voice is on the M channel, which can be processed independently from the reverb present on the S channel, which can also have its width set to taste. The same idea works with a mono bass and a stereo string section where pumping will be avoided. It gives a new perspective to what can be done to a finished mixdown…

Other Modes
Another interesting feature of the alpha compressor is its parallel mode, already used by some sound engineers on their mixing consoles. It’s like turning processing into an effect: The compressed signal doesn’t replace the original but is being added. This is available on the alpha compressor through the Mix controller. The advantage: the signal can be compressed a lot and just added in small quantities wherever needed (lower passages made louder) without losing the original dynamics.

The Auto Fast function seems more familiar, as it optimizes the attack time automatically according to the transient content of the program material…especially in the low end. We don’t always realize it, but the period of a 33 Hz signal is for instance 30 ms, which is a lot longer than the minimum attack time of a compressor (which, on the alpha goes as low as 10 microseconds). The compressor being potentially triggered more than once over the same period, that’s where obvious processing artifacts occur. The Auto Fast mode is available for both attack and release parameters separately to catch the short peaks and then return to the original level smoothly. The smart management of the release makes for a pretty important gain in volume. It is for instance very efficient on percussion.   

Filters
If you think that implementing filters on a stereo compressor is no novelty, then think twice… Not only does the alpha use some hi-pass/lo-pass filters for the sidechain that can be set from 30 Hz to 3.3 kHz,  but Ruben Tilgner also implemented a special one called Niveau Filter in the signal path which some may know under the name of “Tilt” (The 60’s-70’s Quad hi-fi preamps anyone?): the curve is adjusted around a center frequency (42 positions between 20 Hz and 20 kHz with a very useful x10 switch), up to a 3 dB of boost above or below the center frequency. A stunning yet musical action allowing for some very musical corrections without mutilating the original source…

The sidechain features a filter that is switchable from lo-pass (hard left) to hi-pass (hard right), plus everything in between. There is no insert point to the sidechain, though. That’s where some power users may be disappointed as they won’t be able to control the compression process from the outside of the unit.

In Use
The first impression reveals a very clear and open sound. It is one of these machines where it feels like things sound better by just passing through! Today, Hi-end analog proves again that it is the only technology able to get the very last drop out of a worthwhile source. The alpha compressor won’t “save” an over-compressed or muddy mix, but it will shine on acoustic recordings where its fidelity, the elegance of its processing and its subtle color are out of the reach of any digital emulation. Some may have appreciated some parameter recall capabilities: It could be done, but at the expense of a 50 % higher price, and a bigger and heavier unit (à la SPL PQ, if you know what I mean…), which elysia decided against to keep the price at (already) 7.990 Euros.

Is putting what a car costs into a compressor reasonable? This could be discussed… But is it reasonable to be reasonable? “The art of engineering…” according to sound engineer Philippe Teissier du Cros “…is not cost-effective”. Here, this is true in every detail. An investment as good as it looks.