There are many VCA compressors available, at a range of prices, but very few employ a fully discrete gain-reduction element. So what exactly does this design feature bring to the table?
Munich-based Vertigo Sound have a long history in professional audio, and the men behind it — Andy Eschenwecker and Markus Heilmaier — boast many years of experience in servicing vintage gear under the guise of HE Studiotechnik. They were one the first companies in continental Europe to offer racks for coveted vintage modules by manufacturers such as Telefunken, TAB and Siemens, and their Neue Heimat (which translates as 'New Home') racks are still among the finest options on the market. Five years ago, though, they brought their expertise to bear on their first all-original processor design, the VCS2 Quad Discrete VCA Compressor, and established their own brand, Vertigo Sound, to manufacture and distribute it.
At first glance, the VSC2 looks straightforward, albeit beautiful, in its elegant blue enclosure, and it omits some of the inevitable features that seem to have become a standard on other recent compressor designs. But closer inspection reveals some unique — and very useful — features which I'll discuss in a moment. The combination of obvious-but-useful and more 'oblique' features has led to the compressor gaining in popularity — so much so that Brainworx recently created a plug-in that models it, which seems to have attracted a different, but no less enthusiastic, crowd to the hardware version.
VCA compressors are by no means a new concept — the first specimen employing a VCA (voltage controlled amplifier) as the gain-reduction element was developed around 1970 — but transistor VCA circuits have several advantages over tube-based designs. Specifically, they allow for more stable and precise operation, generate less heat, and can be produced at much lower cost, especially when integrated circuits are used — although it doesn't automatically follow that all VCA compressors are cheap designs, as we'll see. In more subjective terms, VCA compressors are often loved for their precision, punch and clarity.
With the exception of some truly exotic limiters, such as the German variable-mu (ie. tube) TAB U73, virtually all compressors developed prior to the early '70s are feedback designs, in which the input to the side-chain is tapped after the gain-reduction element — largely because at the time this was the only way to guarantee stable operation. A VCA based on bipolar transistors, though, can very easily be configured as a feed-forward design, where the detector signal is tapped right after the input, before the gain-reduction element. Although some VCA compressors also offer feedback operation as an option, feed-forward compression is generally considered to be one of the defining attributes of a VCA compressor (though by no means the only one, or the most important).
Many entry-level compressors are VCA designs as well, since the circuits do not necessarily require expensive parts such as tubes, opto cells or audio transformers. However, there's nothing to stop you spending more money on a VCA design in a bid to add rather more to the VCA world — and that's exactly what Vertigo Sound have chosen to do. Today, most VCA compressors are built around an IC-based gain-reduction element, and most — including, famously, those made by SSL — use one or more of the 2180 or 2181 chips made by THAT Corporation in each channel. Very few VCA compressors in current production offer discrete signal paths, but the VSC2 is one of them, and it's the bespoke discrete VCA circuitry that lies at the heart of this design which goes some way to justifying its cost.
The 2U, rackmounting VSC2 is a two-channel design that employs the usual threshold and make-up gain potentiometers, and three six-position rotary switches for ratio, attack and release. This very conventional picture is embellished with a number of additional switches: both audio channels have their own relay-buffered bypass, the unit can be toggled into stereo or dual-mono operation, each channel has a dedicated side-chain high-pass filter and, of course, there's also a power switch, accompanied by a red status LED. The two beautifully lit VU meters resemble classic British designs from SSL and Neve, but they display only gain reduction — so if you require visual feedback for input and output level, this will have to be provided externally.
Before we delve into the special and unique features of the VSC2, I should mention a couple of omissions. First, while the rear panel of the remarkably deep enclosure offers XLR connectors for the inputs and outputs, there's no external side-chain input, which means that the detector signal can only be modified by the built-in filters. Another feature that has gained in popularity in recent years — a dedicated wet/dry control for easy setup of parallel compression duties — is also absent. That said, Vertigo also make the VSM2 Mix Satellite, which is a separate unit that could be deemed the most luxurious of all wet/dry mixers on earth, and it makes a great companion to the VSC2, although it adds still more to the cost.
Very often, it is the cumulative effect of the seemingly small details that makes all the difference in a high-end audio processor, and a number of features prove the extremely high engineering standard of the VSC2. The are six ratio values, ranging from 'Soft', via 2:1, 4:1, 8:1 and 10:1 all the way to 'Brick'. 'Soft' has an extremely wide, soft-knee curve with ratio values between 1:1 and 8:1. This allows for very subtle compression, similiar to a behaviour that would be more typical for opto compressors. Vertigo have coined the phrase 'tiptoe compression' for this mode, and it's apt, as the onset of gain reduction is very smooth indeed. With the higher ratio settings, the knee gets increasingly harder, ultimately leading to the 'Brick' mode, with a ratio of 40:1 (effectively limiting) and straight hard-knee compression.
One unique feature of the VSC2 is the 'stacked ratio', or constant-gain monitoring, principle: when the ratio on the rotary switch is changed, the amount of gain-reduction is automatically adjusted to ensure a consistent output level. Thus, the sound of the various ratio settings can easily be compared, without the change in levels caused by different ratio settings impairing your judgment.
Another not-so-obvious feature is that both side-chain signals are combined in such a way that when the channels are linked, the highest signal peak on either channel results in equal gain-reduction on both channels. Both side-chains are fully active at all times, but their signals never actually get summed, and the result is a very natural stereo image without shifting, and without the troubles that out-of-phase channels may cause with conventional stereo-linking.
While we're on the subject of linking, when the two channels are linked, the controls of channel A, including the threshold and make-up gain potentiometers and the bypass switch, become the master controls, governing the settings for both channels. This is a very neat and genuinely useful feature that few competitors offer, (the Dbx 160SL is the most notable exception).
The six attack settings range from 0.1 to 30ms, the same values that are found on the SSL and API stereo compressors, so they can be considered pretty standard options for VCA bus compressors. The six release values depart from the norm to some degree, but they cover a lot of ground, from a lightning-fast 100ms, via 1.2s, to the programme-dependent 'Auto' mode.
Lifting the lid on the VSC2, it's obvious that this processor has been developed and constructed with a no-expense-spared approach, and there's plenty of evidence of attention being paid to the tiniest of details. As you'd anticipate, components of the highest quality have been used throughout: Alpha potentiometers, Grayhill rotary switches, Jensen input transformers, and Sifam VU meters can all be seen. There are even some bespoke parts, such as the gold-plated toggle switches, manufactured to Vertigo's specifications by the Japanese company Nikkei.
But the really unique 'detail' here is the discrete '1979' VCA blocks, which are potted in ceramic material for thermal stability. Visually, they resemble Dave Blackmer's famous 'Gold Can' designs from the '70s, which can be found in early Dbx and SSL compressors. but according to Vertigo, this VCA design has been developed from scratch, with the aim of combining classic aesthetics with the modern need for transparency. There are four of these discrete VCA blocks here (hence the name 'Quad Discrete VCA Compressor'), two of which are employed in each channel, one in the signal path, and the other in the side-chain.
The approach to this compressor's output stage might be considered sacrilege by analogue audio fundamentalists, in that it's not based on discrete circuitry. Instead, an industry standard 5534 chip acts as current follower, and a THAT 1646 is employed as a balanced line driver.
However, Vertigo point out that the sound of their compressor comes from the VCA itself; the only job of the output stage is to convey it to the outside world as transparently and directly as possible — and the output level is set inside the fully discrete VCA block itself. It's fair to say that the use of dedicated output transformers would not only add further to the build cost, but would also impart some 'colour'. Even if a certain clientele might have preferred the transformer for that very reason, from an engineering perspective, Vertigo have delivered a very viable, and very transparent-sounding, solution.
No matter how you look at it, both the concept and the construction of the VSC2 appear to be almost flawless. Even the user manual is thorough, and contains lots of useful background information — but while that's laudable and reassuring, you hardly ever have to look at it, as the VSC2 is incredibly intuitive to use.
During my tests, it became evident straight away that the VSC2 is a real workhorse that can be used to shape dynamics at all stages of music production. As anticipated, the combination of feed-forward compression, peak detection and the high-bandwidth discrete VCA resulted in very fast and precise gain reduction. While the VSC2 would not be the right choice to soften and 'slow down' signals (something often accomplished through tube stages and transformer saturation), it excelled at controlling transient-rich and very complex, overly dynamic sources: wild, uneven signal peaks were kept at bay in a very effective, yet transparent fashion.
The clarity of the VSC2 comes not only from the accurate, unobtrusive attack and release curves at moderate gain reduction, but also from the elegant, comparatively short signal path inside the unit. The result is that the dynamics are shaped, but the tone of an audio signal is not. If anything, it seems to add a very slight, quite pleasing sheen to the air band, and this subtle coloration gets slightly more pronounced the more you push the make-up gain.
The VSC2 remains clear, stable and open at all times, though, even when applying heavy gain reduction. By comparison, the integrated THAT2181 designs employed by so many other manufacturers always sound, to me, a bit narrow, brittle and thin, tending towards more aggressive behaviour — and I much prefer the Vertigo.
However, the Vertigo's sonic scope certainly is not limited to the cultivated, elegant results it can provide at lower ratios (especially in the 'Soft' mode) and at moderate gain-reduction values. It can also be used to add power, pressure and punch to all kinds of program material. Bass lines, a drum subgroup and even a full mix can benefit from the glossy, muscular force that can be induced using longer attack times. External side-chain inputs would have been a nice addition, but the built in filters already do a great job, especially for drum- and mix-bus compression duties, as they help preserve all the weight and power of the two fundamental octaves.
Sometimes you find the perfect 'sweet-spot' role for a new studio tool very quickly, but that's far from being the case with the VSC2, and for all the right reasons. It's a real workhorse, capable of delivering truly great results in many applications: I love how solid and even a bassline sounds after applying compression with the VSC2; I truly enjoy the way I can make an acoustic guitar sit in the mix (a surprisingly tough task for many compressors); and the punch and body it can tease out of kick drums and snares are downright amazing.
The transparent, fast, clear and glossy results make this a very useful and great-sounding choice for mix-bus compression, in a wide range of musical genres, but so smooth and transparent is the action that it will be equally well suited to serious mastering-compression duties. It really does deliver outstanding results in the majority of 'possible-use' cases.
While the visual appearance of a studio tool might be considered unimportant by some, it's hard not to appreciate the combination of function and beautiful design found in the VSC2. More importantly, the unit feels great to use: touching the knobs and flicking the switches is a real joy, and anything that makes a processor easier to use like this should be appreciated.
No matter how you look at a quality studio tool like the Vertigo VSC2, the enormously high standard of engineering and all those carefully, thoroughly executed design choices quickly become evident in every application. There are certainly more 'characterful' sounding options available on the market, but one of the greatest strengths of the VSC2 is its versatility. It provides outstanding sonic capabilities in virtually all possible applications, with a sonic scope ranging from utmost clarity to a glossy, powerful punch. The admission price will no doubt be considered high by some — especially in the current economic climate — but you have to balance that view with the fact that you're buying pure quality that will last for decades. And not only will a device like this keep much of its financial value over the years: it will also make daily studio work easier and more enjoyable. The VSC2 really does offer all of the desirable qualities a great-sounding VCA compressor should. Stunningly good. .
There's not much competition in the field of dynamic processors that employ a discrete VCA gain-reduction element. The Dbx 160SL is one of them and the API 2500 would be another choice, although the latter does not offer dual-mono operation. IC-based alternatives include the SSL X logic G-series compressor, the Smart Research C1 and C2, the TK Audio BC1 MkII and the Serpent Audio SB4000.