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SPL Stereo Vitalizer MkII

Vitalizer By Paul White
Published April 1997

Paul White tests the latest incarnation of the mysterious Vitalizer, and is still none the wiser about how it actually works.

This latest instalment in the Vitalizer saga, the Mark II, combines the features of the original stereo model with the low‑end compressor found in the Tube model; to bring the cosmetics up to date, the 1U black anodised front panel is screened with a blue marbling effect which closely resembles the laser etching used on the more up‑market SPL products.

It's equipped with both balanced jack and XLR inputs and outputs, and the interfacing is handled by SSM2141 and SSM2142 balanced driver chips, which means that if you use a mono jack to provide unbalanced operation, you won't experience any level changes. Mains power is via an IEC connector, and an illuminated power switch is fitted to the front panel. As this is a dedicated stereo unit, both channels are operated by a single set of controls and this helps to keep the front panel looking clean; the use of simple straight‑sided control knobs gives the whole thing a reassuring, professional look.


Before getting any deeper into what the Vitalizer Mk II does (or appears to do), it's probably best to go through the controls and try to explain their role in the scheme of things. First out of the bag comes Drive, and this sets the level of the signal sent to the side‑chain for processing. A clip LED warns if the drive is too high, but the manual states that different amounts of drive will produce a different result — and I take that as further evidence that the system responds to programme dynamics in some way. The overall level of the mid‑ and bass‑end processing is controlled by the Process knob, and this is quite separate from the high‑end processing, controlled by the intensity knob in the next section along. What happens when you turn up Process depends largely on the settings of the Bass Soft/Tight knob and the Mid‑Hi Tune control. This latter control sets the frequency above which the mid‑range is subjected to processing and, though the range is from 1kHz‑20kHz, a setting of somewhere between 3 and 5kHz is usually best. If you turn it all the way up to 20kHz, you'll be processing a part of the spectrum normally of interest only to bats and dogs, so no audible effect will be apparent. The mid‑range processing is, according to the manual, where amplitude‑dependent phase‑shift comes in to create a sense of loudness without significantly changing the spectral composition of the signal.

Skipping back to the Bass control, this certainly does modify the spectral content of the signal, and it's not difficult to produce a kick strong enough to make most nearfield monitors lose their grip on reality. To accurately evaluate what's going on here, you really do need monitors with a decent bass response. Turning the Bass knob clockwise from the centre to the Hard position results in a tight, punchy bass lift, whereas turning it towards Soft brings in a very deep, less focused bass end capable of shaking bass drivers from their mountings. No sub‑bass generation tricks are used here — it's another case of redistributing and amplifying what's already there. At the same time as you boost the bass, the lower mid range dips to allow the bass to do its thing unhindered. These frequency‑response modifications are closely linked to the Fletcher Munsen loudness curves, and tend to exploit the way the human hearing system perceives music heard at different amplitudes. The outcome is that mixes tend to sound louder and less boxy when they're played back at domestic listening levels.

Despite the technical and cosmetic changes, this box is still a pedigree Vitalizer at heart and produces that characteristic effect of making every part of the spectrum seem clearer and more solid.

Making its first appearance outside the Tube Vitalizer is the Bass Compression control, a one‑knob, automatic compressor designed to act only on the side‑chain portion of the bass‑enhancement signal. The idea is that the average bass energy of a mix can be increased using compression, but because none of the original signal is processed — and because the mid‑ and high‑frequency enhancement components don't pass through the compressor either — you don't suffer the usual compressor problem where bass sounds suck out the high‑end detail. Once the Mid‑High Tune frequency is set and the amount of bass enhancement decided, the overall degree of enhancement can be conveniently adjusted using the Process control. As Process is increased, the bass lifts and the lower mid is simultaneously pulled back. A blue LED comes on when compression is taking place, and because there's only one compressor knob to adjust, setting up is really very fast.

High‑frequency enhancement is controlled by a completely separate section, not by the Process knob. Instead, there's a Frequency knob to set the point above which high‑frequency processing occurs, and an Intensity knob that sets how much processing you hear. The range of adjustment is from 2kHz‑20kHz but, once again, most sensible values seem to be between 3 and 8kHz. The processing involves steep filters and phase manipulation, but no precise details are provided. An illuminated Active button brings the whole enhancement process in and out, while a further knob and bypass switch bring in a simple stereo expander based on the old principle of feeding phase‑inverted signals into opposite channels. This works surprisingly well; if you put the signal into mono, the added components simply cancel out, causing nothing but a slight level change, so there are no compatibility problems.

Vital Signs

Despite the technical and cosmetic changes, this box is still a pedigree Vitalizer at heart and produces that characteristic effect of making every part of the spectrum seem clearer and more solid. The bass enhancement is sensational on dance tracks, though it is equally useful for beefing up wimpy bass guitar, bass synth or kick‑drum sounds in pop mixes. Having the ability to compress the bass enhancement is a useful facility, as it allows you to add more bass energy without allowing the overall level to get out of hand.

The top end of the mix does take on a nice crisp edge when it's processed through the Vitalizer Mk II, but the sound is rather different to what you'd expect from, say, an Aphex Aural Exciter, where new harmonics are added. It's probably fair to say that the harmonic enhancer is capable of the most dramatic results because it isn't limited to working with what's already there — but unless your recordings are absolutely hopeless, the Vitalizer should be able to make some improvement at the high end, and with less likelihood of the end result sounding harsh if a lot of processing is needed.


Even the cheaper Vitalizers tend to be more expensive than traditional enhancers, but I still maintain that they're worth it. I've used the original Vitalizer for a long time now and I like the flexibility it gives me to touch up complete mixes or subgroups. I've never actually used it in mono, so having a stereo model wouldn't limit me in any way at all, and it's obviously easier to set up one set of controls than two. On a practical note, the new output stage is a good move — my old unit still suffers from level changes if I use it unbalanced, but you won't have that problem with this model.

I also like the addition of the compressor and High EQ tune control — I've never felt that I needed them before, but once you get a bit more flexibility, you soon find ways to use it. If you haven't yet had a chance to listen to a Vitalizer, I'd strongly suggest you do so before deciding on what type of enhancer to buy. There are very few unique processors on the market, but this is undoubtedly one of them, and there are very few mixes indeed for which I don't use it to some extent.

Vitalizer Mystery

The Vitalizer has been around in one form or another for some years now, and I know that quite a few of you have bought one, and I have too, so I find it frustrating that I don't really know what it's doing. Look in the manual and you'll see a series of complex EQ curves, and if you overlook the phrase 'dynamic phase shift', you could easily accept the Vitalizer as being simply a different type of equaliser — but there's clearly more to it than that. Though I've tried on numerous occasions, I haven't been able to duplicate the effect of the Vitalizer using conventional EQ, yet it doesn't sound like a typical enhancer either. It's certainly a 'more of everything' box, and it's quite easy to set up once you get the hang of it, but it claims not to add synthesized harmonics or distortion. Like an enhancer, it adds the processed signal to the original untreated sound and, as with an enhancer, the mix sounds more transparent and detailed, but there's also a significant amount of bottom‑end enhancement and mid‑range trickery going on too.


  • Enhancement across the whole audio spectrum.
  • Two distinct bass‑enhancement types.
  • Easy to set up.


  • Still more expensive than most competing enhancers.


There are few mixes that can't be made to sound more appealing or more exciting when processed with a Vitalizer, and this model adds flexibility to the process.