Stereo Vitalizer MK2

Modell 9526

Testbericht in Home Recording Volume 1, USA, von Jon Chapell


SPL Stereo Vitalizer Mk2 – Add stereo magic to your mixdowns

If Sound Performance Laboratory's (SPL) new signal processor were touted merely as a sonic exciter, along the lines of similar units by Aphex, BBE and dbx, it would be a formidable rival. But the fact that it includes several more precise EQ-shaping controls and a secret weapon - the Stereo Enhancer - makes this unit virtually unbeatable, and one of the best things you can do when trying to add life and sparkle to your mixes.

The application is dirt-simple. The unit takes your master stereo signal - which can be anything from a multitrack mixdown to an old cassette to a commercially recorded CD - and gives it more brilliance, clariry, and stereo separation. The results are eye popping, improving virtually everything it touches through some psychoacoustic voodoo.

After throwing a random sampling as it - including solo acoustic guitar, hard rock, vocal accapella and symphonic music - I had to admit that virtually everything sounded more sparkly, or at least more dramatic. This made me curious - almost suspicious. How could my favorite mixes sound even better? Am I simply being fooled, as when people turn off the Dolby on Dolby-encoded tapes and mistake increased fizz for better high-end response?

The answer is yes, you are giving your ears candy when protein is available on the same plate. And there are methods you can employ to get the unit to trip over itself, and not everything will produce pleasant results. But more often than not, of you use the Stereo Vitalizer normally and judiciously, you get great results. Virtually every listener who encountered the Vitalizer (from non-musicians to engineers) agreed the effect was striking, magical.


The Stereo Vitalizer is a 1 RU device with ins and outs on the back, and knobs and switches on the front. There are no hidden configuration routines and no multi-fuction parameter knobs, making the unit very intuitive and easy to learn. Plug your cords into the back, throw on the power switch, and start tweaking. You'll hear instant results (and probably a better sound), and you'll be able to start shaping and improving your sound in about 20 seconds without even cracking the manual. The unit it best "tuned" by ear, anyway, though the manual provdes some valuable pointers.


The unit features both balanced (XLR) and unbalanced (1/4") ins and outs, You plug the stereo output of the signal (either via insert jacks or inline to another component) into and out of the Vitalizer, so that the entire signal is processed. Then, with the Active (bypass) switch you bring the unit in and out of processing mode, tweaking to taste. The front panel controls resemble other sonic exciters in that there is a separate control for the bass, but the Stereo Vitalizer goes further with ist high-frequency processors.

Moving from left to right, there's a separate control for bass boost and compression, and two controls each for the higher frequency bands (Mid-High Tune/Intensity, Hi EQ/Process). The last control is the Stereo Expander, which consists of a single control to vary the effect's intensity, and a push-button to bring it in and out. Pushing the Stereo Enhancer switch in has no effect unless the Active switch is engaged. This means that to have just the Stereo Expander feature active, you have to set the other signal processing controls (the Bass, Process and Intensity controls) to 0. This is not a limitation, as there are many situations where you would pull the Stereo Enhancer in and out, but none where you'd have the Stereo Enhancer going and kick in the other controls (that would sound like bad mixing technique).


The EQ controls are well voiced, with their center positions reflecting typical weak spots in most mixes. The bass boost control is bi-directional. Turning the knob to the left produces a "soft" bass increase, where the bass sounds warmer and rings longer. Turning the knob to the right produces an increasingly "tight", percussive response. There's a compressor control with an LED that tells you when the threshold is crossed and gain reduction occurs. The bass response is further influenced by the Process control, which also acts on the Mid-Hi Tune controls. This Mid-Hi knob is like an intelligent broad-band shelving EQ, using an amplitude-dependent phase-shifting scheme to keep the same perception of loudness without altering the actual spectral composition of the program material (as a graphic EQ does). This is one of the Vitalizer's magical components.

The High EQ acts on specific frequencies, and as such, works in conjunction with the Mid-Hi control. Since the Mid-Hi control boosts frequencies above the center frequency and dampens those below it, some desirable frequencies (such as lead vocals), may get suppressed - sort of a throwing-the-baby-out-with-the-bathware situation. But desirable frequencies being dampened by the Mid-Hi control can be brought our with the High EQ and Process controls. Unlike conventional exciters, the High EQ works with frequencies and harmonics that exist within the program material itself, rather than creating artificial, unrelated ones (which can contribute to eat fatigue).


Processing the entire master stereo signal is the typical way you'd use the Stereo Vitalizer, but there are also other uses. Though it works best on true stereo signals, you can create a "poor man's stereo" rather easily using a mono signal and a DDL Take the direct out of, say, a guitar's mixer channel, feed it through the DDL, and come back into another mixer channel. Set the delay as follows: 100% mix, 1 repeat, 0% feedback, 1-10 ms delay time. Ordinarily, with a delay time this short, you'd get just a comb filtering effect or some phase cancellation, especially over speakers. But because the Stereo Vitalizer works on differing information between left and right channels, your two-channel signal will suddenly surge to life. Vary the delay time to increase the effect. This is one of my favorite applications for the Stereo Vitalizer. Not as wimpy as stereo chorus, but every bit as panoramic.

Sometimes the lead vocal - or anything that's panned straight up the center - diminishes in presence, and side-panned material takes on undue prominence. (This phenomena is similar to what happens in vocal eliminators, because the center-panned signal is reversed-phased and summed with the original, which cancels itself out.) So while side-panned material gains intelligibility and separation, it's sometimes at the expense of the lead vocal. However, SPL recognizes this and recommends using the High EQ and Intensity controls to help bring out these specific frequencies. But doing so birngs in more processing, which adds noise and may require "knob riding".

Noise also comes in two other forms. One is increased sibilance in some already bright vocal material. Another is simply the quiescent noise level. Pushing the Active switch in and out reveals that some fizz is being added, especially if you have the controls set high. While the unit's musicality masks most of that during strong appearance of program material, it can become a problem in fade-outs. But these are very minor caveats, consideirng that 90 percent of the time, a zestier, zingier mix is achieved with minimal tweaking.


There are many situations where some stereo magic is desirable, even in a "perfect" mix. Think of a demo, where you have to get poeple's jaws to drop in a short time. Or if your tape will be heard in less than optimal listening conditions, like a star stereo. And especially if you know your material will be judged under headphones, where you want increased bass and can reap the benefits of maximum separation.

If you're at play in the stereo field, you can't do without the Stereo Vitalizer. It stratifies backing instruments, gives them clarity and intellgibility, and adds exciter-like punch. For situations where something extra is neede - on demos or with old, dull, and over-copressed program material (read: your entire cassette library), a trip through the Vitalizer will provide new vitality and give you an end product that's essentially a new mix - with one push of a button.

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