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SPL Vitalizer

The Vital Ingredient

By using elements of equalisation combined with established psychoacoustic principles, the SPL Vitalizer enhances the entire audio spectrum. Paul White reviews the unit that is now a vital ingredient of his mixes.

Psychoacoustic processors have been around for many years, the most famous and successful being, without doubt, the Aphex Aural Exciter. That unit pioneered the principle of adding small amounts of harmonically-related distortion to a signal with a view to increasing subjective brightness and transient definition. The Vitalizer reviewed here introduces no intentional distortion, relying more on filtering and phase cancellation to create its effect.

Designed and built in Germany, the SPL Vitalizer occupies a conventional 1U rack case and is configured as two independent channels with no linking facility; for stereo use, it is necessary to match the control settings on the two channels. Two versions of the unit are available, offering either jack or XLR connections, but both variations are electronically balanced with a switchable input attenuator allowing connection to systems operating between -10dBV and +8dBu. This is accomplished by means of a 5-position rotary switch (one for each channel) located on the rear panel. It is important to set the right sensitivity as the intensity of the effect is directly related to the input signal level — the manual suggests deliberate overdriving by advancing the attenuator switch a click or so if a larger-than-life effect is desired.

While in the vicinity of the rear panel, it is also worth mentioning the recessed dual-voltage power switch which gives a choice of 115V or 240V operation at either 60 or 50Hz respectively. A ground lift switch is provided which places a resistor between the chassis earth and the signal ground to assist in combating ground loop problems.

The main controls and switches are located on the front panel, configured as two identical channels each with bypass buttons, and there is LED status illumination on all switches. There is an independent section labelled Surround Processor, which controls a simple stereo width expansion system that functions independently of the rest of the processing. In the event of power failure, a bypass relay drops in and routes the input directly to the output which offers a degree of security in live applications.

Unlike a conventional equaliser, the Vitalizer creates its effects by generating a processed signal which is then added to the original. This modifies the frequency response of the signal both additively and subtractively, and because of the filter interaction the effect gives the impression of being dynamically related to the input signal. The result is a perceived increase in bass and brightness while the mid-range is brought into sharper focus, increasing the sense of transparency. Part of the methodology employed is to add low frequency equalisation in such a way that phase cancellation occurs in the lower mid range. This has the effect of simultaneously lifting the bass and pulling back that area of the spectrum that would normally conflict with it, resulting in a very powerful but tightly controlled bass lift with none of the wooliness or vagueness associated with conventional equalisers.

Likewise, at the high end of the spectrum the Harmonics control can be used to pull out transient detail and, though there is some secrecy surrounding the exact principles involved, the process seems to involve dynamic equalisation and phase shift rather than the addition of controlled distortion. This results in a very natural and smooth top end.

Because the system utilises a side-chain approach, it is possible to isolate the processed signal using the Process Solo button. Not only does this allow the user to check how much processing is actually taking place, but it also provides a means of adding the effect via the aux sends and returns on a console.


The first control is a dual concentric pot, the outer ring of which simply controls the absolute output level of the unit. The inner section controls the Process Depth and determines how much of the output from the Sub Bass and Mid-High filters is added back to the original sound. This has no effect on the Harmonics or Stereo Width controls, which operate quite independently. A peak signal LED is fitted to assist in setting up and the best effects seem to be achieved when the input signal level just causes the LED to flash on signal peaks.

The Bypass and Process Solo buttons do exactly as their names imply while the Mid-High tuning control defines the area of the mid range that will be processed. This also affects the operation of the Harmonics control as the harmonics processor derives its input partly from the untreated signal and partly from the output of the Mid-High filter.

The Mid-High filter range is from 1 kHz to 22kHz, and the actual filter characteristic is high-pass, so the higher the setting, the less of the signal is treated. Normally a setting of between 3 and 5kHz produces the best results. A preset pot allows the Q at the cutoff point to be increased, if desired, for special effects. The Harmonics control works quite independently of the Process Depth control and has the effect of enhancing high frequency detail in much the same way as a traditional exciter. Even so, no deliberate distortion is added, the effect being created by a dynamic filter circuit employing fourth-order filters.

The Bass Process control has a centre-off position and produces two distinct sound characters depending on whether it is turned right or left from centre. Advanced clockwise, the sound takes on a very tight, punchy feel while the counter-clockwise direction produces a much deeper, rounder bass. A further button labelled Deep changes the filter response of the Bass Process circuit providing a deeper bass effect. This is a genuinely deep effect and many nearfield monitors are quite unable to register it. The Surround Processor uses the simple and well-established principle of feeding phase inverted signal from the left channel into the right and vice-versa. Used in moderation, this can provide a stereo image that appears to be wider than the speaker placement — the same system is employed in ghetto blasters and suchlike.


Fortunately, the Vitalizer is very easy to set up — providing you approach it logically. By setting the Sub Bass control to off and the Harmonics control fully anticlockwise, the effect of the Mid-High tune control can be heard once the Process Depth control is turned up. By advancing the Bass Process control, a degree of bass enhancement can then be applied, the exact character being determined by the setting of the Deep switch and the direction of rotation of the control. Finally, the Harmonics control can be used to liven up the high end. The Surround Processor is, as stated, an entirely separate effect and is best turned right down unless it is needed. It is not affected by the Bypass button.

The subjective result of processing via the unit is to increase the perceived sense of loudness of a mix while simultaneously enhancing the sense of space. The loudness aspect is closely related the Fletcher Munson effect, which describes the way the ear reacts to sounds of different intensities. While the Vitalizer does seem to produce this 'bathtub' frequency response curve, the way in which it employs phase cancellation certainly appears to add a sense of transparency and life to music that standard equalisers can't match.

As for the Surround Processor section, I feel this was thrown in as a bonus rather than being integral with the main purpose of the device. It works perfectly well, though control settings beyond the 2 o'clock position are somewhat excessive for normal use.


In terms of audio quality, the Vitalizer is quiet enough for all serious audio applications, though by virtue of the very fact that it can be used to apply high frequency boost the level of noise present in the original material does have to be taken into consideration. Also, the use of high frequency enhancement does tend to emphasise any distortion already present in a signal, so if you think you have a distortion problem, the first thing to check out is the source. Likewise, over-processing the top end can aggravate sibilance problems where these exist. These comments in no way imply criticism of the unit, but rather point out areas in which the engineer needs to exercise awareness, regardless of whose processor he or she is using.

From a creative viewpoint, I have found the Vitalizer virtually indispensable in fine-tuning my mixes simply because it allows me to equalise sounds in a way that none of my equalisers come close to matching. The subjective effect is like that of an exciter that works not just at the top end but right across the audio spectrum; somehow, everything seems louder but, at the same-time, there's more separation. And for the no-holds-barred creative engineer, the Vitalizer represents an easy way to add the punch and sizzle to a recording that the end user seems to demand. I've been using the predecessor to this unit in my own studio for a couple of years, and I'd certainly be reluctant to approach a mix or sweetening session without it. The device has lots of valid applications from regular mixing to broadcast, from video-post to tape duplication — in fact any area where music needs to be made to sound more enticing to the end user. I really hope this product takes off in the UK because I believe it has something genuinely unique to offer.

Further information

SPL Vitalizer (XLR version) £757.88 inc VAT.
SPL Vitalizer (jack version) £699.13 inc VAT.

The Home Service, (Contact Details).

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Previous Article in this issue

I Sync Therefore I Am

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Digital Effects

Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - May 1992

Gear in this article:

Studio FX > SPL > Stereo Vitalizer

Review by Paul White

Previous article in this issue:

> I Sync Therefore I Am

Next article in this issue:

> Digital Effects

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