SPL Tube Vitalizer

SPL's Vitalizers work in mysterious ways to give added life even to good recordings. Now a new model incorporates valves, compressors, filters, and extra controllability, for yet more audio magic. Paul White opens a box of tricks.

We may claim to strive for accuracy when recording, but if there's a box we can plug in to make things sound even better, we tend to use it. In fact, it may be part of the human condition that we tend to be dissatisfied with real life, preferring instead the blue whitener in our washing powder, the rose tint in our spectacles, or the holiday snaps with vibrant, oversaturated colours.

Exciting Background

Nobody has really got to the bottom of psychoacoustics, as yet, and it's still not fully explained why taking a perfectly good recording and enhancing it using various processes (such as harmonic excitement or dynamic EQ) makes it sound somehow more real and alive. Perhaps it's a limitation of the stereo loudspeaker reproduction system that's being compensated for by the enhancement process, or maybe the lack of visual clues to reinforce what is going on in music makes it necessary to provide more audio clues. Whatever the reason for the effect of psychoacoustic enhancement, the original recording usually sounds quite flat and disappointing once the effect is turned off.

The first box to enhance audio in this way was the Aphex Aural Exciter, which was not originally available to buy, but had to be rented from Aphex and credited on any commercial releases on which it featured! The Aphex range has gone from strength to strength, but now there are lots of different makes and models to choose from, all working on different principles. Regular readers will have noticed my occasional references to a device called the SPL Vitalizer, which I use in my own studio. This works on a principle quite different to that of other enhancers — it doesn't generate new high‑frequency harmonics in the way that the Aphex process does, and unlike other dynamic EQ‑based approaches, the Vitalizer appears to produce an equalised side‑chain signal which is added to the original to produce both summation and cancellation effects in frequency and phase. I've tried to get the German designer to explain the process to me on several occasions, but I still come away little the wiser.

What's New?

Before looking at the new Tube Vitalizer under review, it's probably worth outlining a couple of the features of the original solid‑state model. Enhancement is applied right across the audio spectrum, rather than just at the top (as was the case with most early enhancers), and a unique bass control provides a deep, rounded bass boost when moved in one direction, and a tight, punchy bass when moved in the other, making it very flexible on all types of music. I believe that when the bass end is being boosted, phase cancellation occurs in the lower‑mid range to prevent the effects of the bass boost spreading higher up the spectrum, where you don't want them.

The middle part of the spectrum is controlled using a Mid/High tuneable filter, but again, the operation of this isn't at all straightforward, as the effect depends both on signal intensity and on the setting of the Process control. A further stage of processing, based on a mix of the Mid/High filtered signal and the original input, is then filtered again to produce the necessary high‑end sizzle.

As far as I can see, all these features have been retained in the Tube Vitalizer, but in addition to the tube output circuitry, several other new features have been added. Now there are two compressors in each channel, one for the high end and one for the bass end (but affecting only the side‑chain portion of the audio signal), and the output stage includes limiters. There's also a pair of switchable LC (inductor/capacitor) filters, one for the high end and one for the low end, as well as a bypass switch for the tube circuitry. If all this sounds confusing at the moment, don't worry — there's a lot going on in this unit.

Vital Signs

The Tube Vitalizer is a beautifully styled, 2U box dedicated to processing stereo signals — settings for both channels are made by the same set of controls. Behind the pale gold front panel glow three valves (ECC83s), which are clearly visible through black mesh windows. Rear panel connections provide balanced inputs and outputs, both on conventionally wired XLRs and balanced jacks. The Vitalizer would normally be connected via console insert points or placed in‑line between one piece of equipment and the next. If you decide to use it unbalanced, you don't lose half your signal, and since most consoles have unbalanced insert points, this can only be a good thing.

When the full Vitalizer controls are brought into play, it's as though everything becomes warmer and brighter at the same time.

The main controls are located to the left of the machine, but until you've figured out what does what, they can appear rather confusing. The top three knobs relate specifically to high frequency enhancement, while the knobs on the bottom row relate mainly to low frequency enhancement and Hi‑Mid tuning. To the right, there are separate attenuators for the two output channels, both fitted with lovely bakelite knobs, and switches to select between attenuation or limiting. The twin VU meters can be switched to monitor the input or output signal, and there's a button to bypass the tube part of the circuit if necessary.

After the unit is switched on, the power to the valves increases, in order to prolong their useful life, so you need to wait a minute or so before you can start work. To turn the effect on, you have to switch in the Process button, after which the controls need to be set up in a logical order to make sense. The Tube Vitalizer process is, to some extent, level dependent, so an input Drive control is used to match the unit to the device driving it. There's no absolute setting that you need to adhere to — the more drive you use, the more pronounced the effect. To start with, a setting near the centre is usually best. Turning the Bass control either way from centre will introduce either the Soft or Hard bass enhancement, but you'll only hear this if the Process Level is turned up. This control acts an overall 'effect amount' for the lower and mid frequencies, while the Intensity knob directly above it serves a similar function for high frequency enhancement — though, as with all aspects of the Vitalizer, not everything is quite as it seems. In addition to providing an 'effect amount' control, Process Level also affects the way in which mid‑band frequencies are damped, so there's quite a high degree of interactivity between the various controls.

The Mid‑High tune knob controls a broad‑band shelving filter, which boosts frequencies above the filter point, while attenuating those below it. Much of how this works is tied up with phase relationships but, unlike the original Vitalizer, the Tube Vitalizer has a separate High Frequency knob, to give more precise control over the frequency range in which high frequency enhancement occurs.

The Process button acts as a bypass, and uses relay switching to route the input directly to the output, either when the effect is bypassed or in the event of a power failure. When the valves are switched in, they take over from the solid‑state output driver circuitry, but from what I can understand from the manual, they also introduce a subtle amount of stereo width expansion. A limiter can be switched in, which gently holds down any signals that attempt to exceed the 0dB level.

As touched upon earlier, there are two compressors, which act separately on the bass and top‑end components of the processed signal, without affecting the direct component. These are each controlled by a single knob, and an adjacent blue LED lights when gain reduction is taking place. The effect is to enrich the sound, making it seem smoother and more dense. The other newcomers are the LC filters, though the manual provides little information as to the filter characteristics. When these are switched in, there is a subtle difference in sound, but not so subtle that you don't hear it. At the top end, the sound becomes slightly more focused and open, whereas the bottom‑end LC filter somehow conspires to round out the bass end a little more. Many old classic equalisers use LC circuitry, but because of the high cost of the wound inductors, most modern designs try to manage without them.

In Use

Having used a conventional Vitalizer for some years now, I felt I should have been able to jump straight in and use this box, but it still took me a few minutes to get used to the new controls. Because of the interactive nature of the controls, you really need to set them up in a logical order, and fortunately, an example is provided in the manual. However, the manual is pretty thin on practical information otherwise, preferring, rather, to present graphs of frequency response. Having said that, it's worth persevering, because every control on this box makes a positive contribution to the overall sound which, with a little practice, can be very finely crafted. For example, the tube output stage used on its own adds a noticeable amount of warmth.

When the full Vitalizer controls are brought into play, it's as though everything becomes warmer and brighter at the same time — it's a very comfortable effect, and if you switch the process out again, the original sound can seem very boxy or nasal. The compressors also help control the effect on signal peaks, while making sure that lower levels receive adequate amounts of treatment. If you can imagine all the best attributes of a really good tube EQ combined with a more conventional enhancer and a dynamic equaliser, you'll come some way to understanding what the Tube Vitalizer is all about. Where this unit scores is that as you increase one frequency, any others that might conflict with it are automatically decreased, making the whole procedure less hit and miss. Much of the process is linked to the way in which the human hearing response changes with signal level, but I think I'm also right in saying a lot of the Vitalizer principles were discovered almost by accident as designer Wolfgang Neumann experimented with some of his more radical EQ circuits.

Summary

The Tube Vitalizer isn't something you can just pick up and expect to use immediately — it's essential to experiment for an hour or so to get a feel for what controls produce what effects. I feel the controls could have been better explained in the manual (indeed, they could have been given more logical titles in some cases), and it would also have been easy to use front‑panel graphics to divide them into more logical sections, but even so, it doesn't take long to figure out what does what. And when you do get the hang of it, what a powerful tool this is! The amount of control you have over the tonality, weight, and balance of your signal is just wonderful.

If you want the Vitalizer effect at a bargain price, check out the dedicated stereo Vitalizer. If you really want the full works, however, this is the box to go for. It does sound smoother and richer than the solid‑state models, as well offering far more control, but the trade‑off is that you have more controls to juggle — and more figures to juggle when it comes to paying for it. This isn't a budget box, nor would I expect it to be. It's priced on a par with other esoteric equalisers, but for those doing serious recording, mastering or post‑pro sweetening, it's well worth the cost. I'd happily upgrade my old model tomorrow, but as I'm in a similar fiscal position to most of you, I guess it's not going to happen. To those lucky ones who can justify a Tube Vitalizer, all I can say is that I think you'll like what you hear.