TEST: SPL Vitalizer MK3-T

 Nearly every sound engineer is familiar with the problem. Due to the incredibly high number of plugins and tracks, limited only by CPU performance and SSD access speed in DAWs, the risk of different signals overlapping and thus canceling or masking each other increases immensely. To counteract this, SPL from Niederkrüchten, Germany, has launched the third version of the SPL Vitalizer MK3-T, developed and manufactured in Germany, which aims to bring more transparency to the mix through a combination of psychoacoustics and audiometry.

The Concept of the SPL Vitalizer MK3-T

One of the crucial elements of the patented Vitalizer circuit is the so-called demasking of signals that are overlaid by other signal components. The Vitalizer correlates the perception timing of a frequency significantly with its volume. Through a wafer-thin temporal offset of loud frequencies, quieter sound nuances are revealed that were previously hidden by overlapping elements and thus made audible. The system is based on the non-linear sensitivity of human hearing developed in 1930 through the so-called Fletcher-Munson curves. These curves, nowadays refined by the ISO 226:2003 standard, illustrate the constant perception of loudness across the frequency spectrum. This results in a constant sound pressure level when a listener is played pure, even tones. According to the manufacturer, the newly created signal sounds more lively, has more details, and possesses higher loudness.

The Construction of the SPL Vitalizer MK3-T

The SPL Vitalizer Mk3-T presents itself with a massive, black anodized aluminum front panel 4 mm thick. The housing impresses with high-quality, solid steel construction and an optically attractive black powder coating, which replaces the gold lacquer used on previous models. Due to a higher internal audio voltage of +/-18 V, the sound is said to have improved even further compared to versions 1 and 2. Despite its 1U design and moderate depth of 300 mm, the product weighs in at nearly 6.1 kg, which reflects, among other things, the solid construction of the product.

A total of 5 controls are responsible for adjusting the de-masking effect:

Drive: The control of the filter network is regulated by the Drive knob, with the control range between -20 dB and +6 dB. In the center position (0 dB), the drive level corresponds exactly to the input level.

OVL: The OVL LED signals potential overdriving of both the input stages and internal processes. The OVL LED lights up 3 dB before overdriving to ensure that the Vitalizer always produces an optimal sound.

Bass Sound: The Bass Sound control allows the selection between two bass timbres.

Soft: By moving the Bass Sound control from the center position (0) to the left, the bass range becomes soft and warm, which is referred to as "Soft."

Tight: Moving the Bass Sound control from the center position (0) to the right results in a dry and percussive bass range, referred to as "Tight." The square representation of the scaling points on the right side symbolizes this contoured, tight bass sound.

Bass Comp: The Stereo Vitalizer Mk3-T is equipped with a spartan "one-knob" compressor for the bass processing path, which leaves the original bass content untouched. Attack, Release, and Threshold are preset. By increasing the Bass Comp value, both the compression ratio and the threshold are adjusted. The compressor works with a soft-knee control characteristic to sound as inconspicuous as possible. The Gain Reduction LED "GR" indicates when the compressor is active.

Mid-Hi Tune: The Mid-Hi Tune control sets the onset frequency or lower cutoff frequency, above which frequencies are boosted with the selected Process value, or below which frequencies are attenuated. The control range of the Mid-Hi Tune knob extends from 1.1 kHz at the right stop to 22 kHz at the left stop. A Sovtek 12AX7 dual-triode tube in the filter path creates a mixing ratio between the original signal and the filter output. The tube adds its typical overtone characteristics and gives the "Mid-Hi Tune" signal a softer sound signature.

Process: The Process control adjusts the intensity of Bass and Mid-Hi Tune in relation to the original signal and performs attenuation of dominant mid-frequencies.

For additional sound processing, the following controls are available:

LC-EQ: The LC-EQ is a mid-high tone processing stage, built around a passive coil-capacitor network (LC). The LC-EQ increases presence and definition in the midrange, especially for typical mid-range instruments such as voices. The frequency is adjustable between approximately 2 kHz (Low) at the left stop and approximately 20 kHz (High) at the right stop. Coils are known for their pleasant sound image in filter circuits. In the 1960s, coil filters were often used, which were later frequently replaced by RC filters (resistor-capacitor network) due to the high price.

Intensity: The Intensity control determines the level of the LC-EQ. As intensity increases, the amplification of the set high and overtones increases. At the same time, the perception timing is shifted so that quiet high-frequency components are not masked by loud ones. This improves speech intelligibility and clarity and increases the brilliance of any audio signal without sounding harsh.

Stereo Expander: The Stereo Expander widens the stereo base width and improves the spatial impression by simulating a decentralized localization of the sound source outside the speaker plane. The Sovtek 12AX7 dual-triode tube is also used in the Stereo Expander, mixing the right and left channels. The tube adds its tube-typical harmonic spectrum to the stereo signal, consisting mainly of even overtones. In addition to widening the stereo image, the tube is said to enable greater depth layering, clearer drawing of reverb spaces, and a softening of the high-frequency range.

The Vitalizer Mk3-T is activated by the On switch, which lights up when activated. In bypass mode, the switch does not light up. A flashing switch signals the "Warm-Up" mode, in which the tubes are brought to the optimal operating temperature.

The Rear Panel of the SPL Vitalizer MK3-T

All inputs and outputs of the Vitalizer Mk3-T feature Neutrik XLR sockets with gold-plated contacts as well as Neutrik TRS sockets. Both the XLR and jack sockets are connected in parallel, and the signal transmission is electronically balanced with a nominal level of +6 dBu. On the output side, two signals are provided per output, meaning that the processed signal can be routed to two different devices. If the inputs are double-assigned, the two input signals are mixed.

To prevent ground loops, the Vitalizer MK3-T has a separate ground-lift switch. Finally, on the left side of the housing, there is a mains selector switch that allows voltage selection between 230 volts and 115 volts, and an IEC socket with fuse access.

The SPL Vitalizer MK3-T in Practice

As expected, the application area of the SPL Vitalizer MK3-T is the stereo sum or, as an insider tip, a corresponding bus where the danger of masking is always present. In my opinion, choir tracks would be the first choice here, as high soprano passages in female vocals can be very dominant depending on the frequency and quickly lead to an uneven sound image. If you combat this problem with the corresponding automation, the choir quickly sounds unbalanced, as in the Hollywood comedy Sister Act during the first choir rehearsal.

After processing the first sound files, I inevitably felt reminded of a loudness circuit on a very high-quality stereo system in the result. The SPL Vitalizer MK3-T provides a real enrichment of the signal, especially in the deep bass range as well as in the very fine highs, which of course inevitably goes hand in hand with a slight lowering of the mids. However, the sonic result is far from as "blunt" as a simple bass and treble boost using a shelving filter; you can clearly hear that the algorithm attaches itself to different instruments. You can notice it very nicely in the high range, for example, how the hi-hat in the drums gains significantly more presence without sounding obtrusive.

The SPL Vitalizer MK3-T can particularly show its strengths when it comes to refining inferior or muffled-sounding source material and giving it a significantly more pleasant touch. For example, the SPL Vitalizer MK3-T would be a very good tool for remastering old recordings that may have been rotting on some tapes in archives for ages, just waiting to be re-released.

In summary, one must say that the SPL is a very good tool, especially for mastering and subgroup areas, which can intervene in the sound event with very fine accents, but also brashly if needed, to give the source material a higher-quality finish.

Expanding on the Technical Aspects

The SPL Vitalizer MK3-T employs several sophisticated circuit designs to achieve its unique sound-shaping capabilities. One of the key elements is the use of a hybrid analog-tube circuit. The incorporation of the Sovtek 12AX7 dual-triode tube in both the Mid-Hi Tune and Stereo Expander sections adds a subtle layer of harmonic richness to the processed signal. This tube imparts a slight coloration that many engineers find pleasing, especially when dealing with digital sources that may sound somewhat sterile or lacking in depth.

The Bass Sound control deserves special attention for its innovative approach to low-frequency management. Unlike traditional bass boost circuits that simply increase gain at a fixed frequency, the Vitalizer's bass processing is more intelligent. The "Soft" setting provides a gentle, warm boost that enhances the fundamental frequencies of bass instruments without muddying the mix. On the other hand, the "Tight" setting focuses on the upper harmonics of bass sounds, adding definition and punch without excessive low-end buildup. This dual-mode bass enhancement allows engineers to tailor the low end to suit different genres and mixing situations.

The LC-EQ section is another standout feature that sets the Vitalizer apart from typical equalizers. By utilizing a passive inductor-capacitor network, this stage imparts a musical quality to the midrange and high frequencies that is difficult to achieve with active op-amp based circuits. The use of inductors in audio circuits has largely fallen out of favor due to cost and potential for interference, but when implemented correctly, as in the Vitalizer, they can provide a smooth, natural-sounding boost that enhances clarity without harshness.

Application in Various Mixing Scenarios

While the Vitalizer MK3-T excels in mastering applications, its versatility extends to various mixing scenarios. For instance, when working with dense rock mixes, the device can help carve out space for each instrument. The Mid-Hi Tune control, in particular, can be invaluable for bringing out the attack of guitars or the breathiness of vocals without resorting to excessive EQ boosts that might lead to harshness.

In electronic music production, the Stereo Expander can add width and depth to synthesizer pads and effects, creating a more immersive soundstage. The Bass Comp feature is especially useful in this genre, allowing for tighter, more controlled low end that translates well to club sound systems.

For acoustic and jazz recordings, the Vitalizer's subtle enhancement capabilities shine. The tube-based circuitry can add a touch of warmth and dimensionality that complements the natural timbres of acoustic instruments. The LC-EQ, when used judiciously, can bring out the air and intimacy of such recordings without sounding artificial.

Comparison with Software Alternatives

In the age of digital audio workstations and plugin processors, hardware units like the SPL Vitalizer MK3-T face stiff competition from software emulations and digital processors. However, many engineers still prefer the tactile experience and unique sonic character of hardware. The Vitalizer's analog circuitry, especially its tube stages, imparts a subtle but noticeable depth and dimension that is challenging to replicate exactly in the digital domain.

That being said, software alternatives offer advantages in terms of recall, automation, and the ability to use multiple instances. Some plugins attempt to model the Vitalizer's circuitry, and while they can come close, discerning ears often note that the hardware still has an edge in terms of depth and analog "mojo."

Integration into Modern Workflows

Despite its analog nature, the SPL Vitalizer MK3-T can be seamlessly integrated into modern, hybrid mixing setups. Its balanced XLR and TRS connections allow for easy patching into analog summing mixers or as an insert on the master bus of a digital audio interface. For those working primarily "in the box," the Vitalizer can serve as a final analog stage before conversion back to digital, adding a touch of analog flavor to otherwise purely digital productions.

Some engineers have found creative ways to utilize the Vitalizer in parallel processing chains, blending its processed signal with the dry signal for more subtle enhancement. This technique can be particularly effective when processing full mixes or subgroups, allowing for precise control over the amount of "vitalizing" applied.

Long-term Reliability and Maintenance

As with any high-end audio equipment, the longevity and reliability of the SPL Vitalizer MK3-T are important considerations. The unit's robust construction and quality components suggest a long service life, but as with any tube-based equipment, periodic maintenance may be necessary. The 12AX7 tubes will eventually need replacement, though their lifespan can be quite long if the unit is well-cared for.

The unit's internal voltage of +/-18V provides ample headroom, which contributes to its clean and dynamic sound. However, it also means that the unit generates some heat during operation. Proper ventilation is essential, especially if the Vitalizer is rack-mounted alongside other equipment.

Conclusion

The SPL Vitalizer MK3-T represents a culmination of decades of audio engineering expertise. It offers a unique approach to sound enhancement that goes beyond simple equalization or dynamics processing. Its ability to unmask and clarify complex audio material makes it a valuable tool in both mixing and mastering contexts.

While it comes with a learning curve and a price tag that reflects its high-end status, engineers who take the time to master its controls are rewarded with a device capable of adding polish and dimension to a wide range of audio material. Its analog circuitry and tube stages provide a character that many find preferable to purely digital solutions.

Ultimately, the SPL Vitalizer MK3-T is not a one-size-fits-all solution, but rather a specialized tool for discerning audio professionals. Its strengths lie in its ability to enhance and clarify without introducing harshness, and its capacity to add depth and dimension to two-dimensional recordings. For those willing to invest the time and resources, it can become an indispensable part of their audio processing toolkit.

Whether used subtly to add a finishing touch to a well-balanced mix or more aggressively to rescue problematic recordings, the Vitalizer MK3-T proves that there's still a place for high-quality analog processing in today's largely digital audio landscape. It's a testament to SPL's commitment to pushing the boundaries of audio technology while respecting the virtues of classic analog design.