TEST: SPL PQ

 It's always fascinating when two diametrically opposed worlds collide head-on, engaging in their beloved trench warfare. A battle that has been raging for decades now primarily takes place in our beloved recording studios, regardless of their size, level of professionalism, or equipment. We're talking about internal versus external, hardware versus software, or more precisely, outboard gear versus plugins. It's tedious to rehash the oft-cited arguments about price, sound quality, habitus, and the "completely dumbed-down ear of the consumer," which we won't be doing here.

However, a current interim report on the state of play would note the introduction of a new player on the outboard gear team, one that's attracting attention with its massive presence and a very high transfer fee. We're referring to the new flagship from the German 19-inch rack specialist SPL, which is sending the SPL PQ, a formidable colossus, onto the playing field. Let's make way for an equalizer of a very special kind.

Construction

The SPL PQ enters the arena as a mastering stereo equalizer, filling a niche that nowadays is mostly handled entirely digitally within the DAW. Alongside compressors and limiters, all types of EQs are found in the signal chain, at the end of which stands the final stereo file. It's becoming increasingly rare for the sum to be converted again before the final mix and sent through corresponding outboard gear, and when it is, this is usually reserved for more economically advantaged studios. High-quality conversion with appropriate management requires maximum quality in the signal flow to ensure that rerouting the signal is sonically worthwhile and doesn't potentially reduce the quality of the end product. To guarantee this, the product used must possess quite a few features that the plugin armada cannot offer. We're curious to see if it's worth putting down nearly five and a half grand for this top dog.

In terms of dimensions and weight, the SPL PQ falls into the same category as the recently released SPL Iron compressor. Four rack units high and weighing over 15 kilograms, this product, once laboriously unpacked, immediately finds its way into the rack, never to be moved again. As always with SPL, the workmanship is perfect, and the construction is solid down to the last detail. The behemoth is available in black and red.

Controls

Even though the 30 black rotary knobs with 41 detents each, along with 22 push buttons and several mini-switches, might initially leave the user in awe, the SPL PQ appears very familiar, almost "normal" upon second glance. Five fully parametric bands per channel may represent a multiple of what conventional analog equalizers offer the user, but in use, they are virtually self-explanatory. SPL employs their proprietary 120-volt technology, which stands for maximum headroom in the processing and minimal coloration of the signal. Thus, they confront the usual audio circuits, which operate with +/- 15 volts, with an operational amplifier level of +/- 60 volts, which allows for an almost twice as high dynamic range compared to conventional circuits.

As with the SPL Iron, the Stereo Link and Auto-Bypass functions have been integrated into the central control panel, with the latter function deserving special attention. A rotary control allows you to set a time interval at which the SPL PQ automatically switches on and off. This is intended to keep the ear fresh and prevent the switching from being done by hand, which might prepare the ear for the expected difference. A very practical feature.

The Stereo Link switch causes both channels to adopt the settings of the right channel's bypass switch and proportional Q switch. Since the device is essentially designed as a dual mono device, the controls on both sides still need to be adjusted manually. However, this also allows operation as two high-end mono EQs, which will undoubtedly find its application in practice.

A look inside the product makes the German engineer's heart beat faster. Excellent workmanship made in Germany, oversized components like the built-in toroidal transformer, good heat dissipation, and optimal shielding between components speak a clear language. Another special feature is the very large overlap of possible frequencies within the frequency bands. Up to three bands can share and process a specific frequency range.

However, with extreme processing, one should keep an eye on the signal chain after the SPL PQ. Due to the 120-volt technology, the SPL PQ works internally without distortion, but the device does not have an output control. Therefore, one should always keep an eye on the input range behind the EQ to ensure that subsequent products don't negate the painstakingly generated distortion-free signal. However, a toggle switch can, if necessary, quarter the +/- 20 dB level setting, resulting in a +/- 5 dB version.

In Practice

But what good are the best measurements and most massive constructions if the sound doesn't at least somewhat justify the hefty price tag? This brings us to the next dilemma. What does "good sound" even mean? Isn't this ultimately a deeply subjective perception? Aren't we mixing and mastering for a clientele that still attests to a good sound on a thoroughly catastrophically overdriven album like "Death Magnetic"?

Therefore, one should first consider the basic orientation of the SPL PQ. If one wanted to encapsulate the basic sound of the EQ in an adjective, only the word "neutral," paired with "clean," comes to mind. What at first glance seems unbeatable in terms of irrelevance turns out, upon close listening, to be a precision instrument that captures individual frequencies with surgical accuracy and deliberately bends the frequency curves. The targeted saturation with which other devices flatter the ear through overtones and compression will not be found here. The SPL PQ simply has no inherent sound, which cannot be valued highly enough in the realm of a mastering EQ.

Even slight level adjustments have a very strong impact on the overall sound and effortlessly assert themselves in the soundscape. Here, the ability to switch between a "constant" and a "proportional" Q works true musical wonders. This switch influences the bell shape of the Q factor. In the constant Q setting, the Q factor always remains the same, regardless of how much the filter band is boosted or cut. A proportional Q filter, on the other hand, increasingly incorporates neighboring frequencies into the work process with stronger processing, increasing the bell shape. For targeted interventions in the sound image, one will tend to resort to the constant Q variant, while a proportional Q filter works more "musically."

Expanded Technical Specifications

To delve deeper into the technical prowess of the SPL PQ, let's examine some of its key specifications:

1. Frequency Range: The SPL PQ covers an expansive frequency range from 10 Hz to 30 kHz, ensuring that even the most subtle sub-bass and high-frequency details can be manipulated with precision.

2. Filter Types: Each of the five bands per channel offers a choice between peak, high shelf, and low shelf filter types, providing maximum flexibility for shaping the frequency response.

3. Q Factor Range: The Q factor can be adjusted from 0.5 to 15, allowing for extremely narrow surgical cuts or broad, smooth boosts.

4. Gain Range: Each band offers +/- 15 dB of boost or cut, with 0.5 dB increments for fine-tuning.

5. THD+N: Less than 0.001% at +4 dBu input level, showcasing the unit's exceptional clarity and low distortion.

6. Dynamic Range: Greater than 125 dB, thanks to the 120V rail technology, surpassing most digital systems.

7. Frequency Response: +0 / -0.5 dB from 10 Hz to 100 kHz, ensuring transparency across the entire audible spectrum and beyond.

8. Crosstalk: Better than -90 dB at 10 kHz, maintaining excellent channel separation.

9. Input Impedance: 10 kΩ balanced, allowing for easy integration with a wide range of audio equipment.

10. Maximum Input Level: +34 dBu, providing ample headroom for even the hottest signals.

11. Output Impedance: 150 Ω balanced, ensuring optimal signal transfer to subsequent devices.

12. Maximum Output Level: +34 dBu, matching the input capabilities and maintaining signal integrity throughout the chain.

Additional Features and Considerations

The SPL PQ's design philosophy extends beyond mere technical specifications. Its user interface has been meticulously crafted to enhance workflow efficiency in professional mastering environments. The large, easily readable VU meters provide instant visual feedback on signal levels, while the Auto-Bypass function, with its adjustable interval, proves invaluable during extended mastering sessions by combating ear fatigue.

One aspect that sets the SPL PQ apart from many of its competitors is its dual-mono design. This approach allows for true stereo processing when needed, but also opens up possibilities for creative mid-side processing techniques. By treating the left and right channels independently, mastering engineers can address stereo image issues with unprecedented precision.

The unit's build quality deserves further mention. The robust chassis isn't just for show; it provides excellent shielding against electromagnetic interference, a crucial consideration in today's studios filled with potential sources of noise. The high-quality potentiometers and switches are rated for thousands of hours of use, ensuring longevity in demanding professional environments.

Comparison with Digital Alternatives

While the SPL PQ stands as a monument to analog excellence, it's worth considering how it compares to high-end digital equalizers. Many will argue that top-tier plugins can achieve similar results at a fraction of the cost. However, the SPL PQ offers several advantages that are difficult to replicate in the digital domain:

1. Analog Warmth: While the SPL PQ is designed for neutrality, it still imparts a subtle analog character that many find pleasing, especially when pushing the unit to its limits.

2. Tactile Control: The physical interaction with high-quality knobs and switches provides a level of control and connection to the music that many find lacking in mouse-based interfaces.

3. Zero Latency: Unlike digital systems, which introduce some degree of latency, the SPL PQ operates in real-time, allowing for immediate audition of changes.

4. Reliability: With no reliance on computer systems or software updates, the SPL PQ offers a level of stability and longevity that can be appealing in mission-critical studio environments.

5. Resale Value: High-end analog gear often retains its value better than digital alternatives, which can become outdated as technology advances.

Integration into Modern Workflows

Despite its analog nature, the SPL PQ is designed to integrate seamlessly into modern, hybrid studio setups. Its balanced XLR inputs and outputs allow for easy connection to high-end AD/DA converters, enabling its use as an insert in a DAW-based workflow. This flexibility allows engineers to combine the best of both worlds, leveraging the SPL PQ's analog processing alongside digital plugins and editing tools.

For studios working primarily in the digital domain, incorporating the SPL PQ into the signal chain requires careful consideration of the conversion process. The quality of the AD/DA converters used becomes crucial, as any shortcomings in the conversion stage could negate the benefits of the SPL PQ's pristine analog circuitry. This consideration further underscores the importance of viewing the SPL PQ as part of a holistic mastering system rather than an isolated component.

Long-term Considerations

Investing in a piece of equipment like the SPL PQ is a significant decision that goes beyond immediate sonic benefits. Prospective buyers should consider the long-term implications:

1. Maintenance: While built to last, any analog device will require periodic maintenance to ensure optimal performance. Factoring in the cost of professional servicing and potential part replacements is advisable.

2. Future-proofing: As digital technology continues to advance, the question arises of how long top-tier analog gear will remain competitive. However, the enduring appeal of classic analog equipment in many studios suggests that well-designed analog tools like the SPL PQ may have a longer shelf life than some digital alternatives.

3. Training and Familiarity: Mastering engineers accustomed to working entirely in the box may face a learning curve when incorporating the SPL PQ into their workflow. The investment in time to fully understand and leverage the unit's capabilities should be considered part of the overall cost.

4. Client Perception: In some markets, the presence of high-end analog gear like the SPL PQ can be a selling point for a studio, potentially attracting clients who value a hybrid analog/digital approach.

Conclusion

With the SPL PQ, Wolfgang Neumann's team has brought a mastering EQ to market that is poised to overshadow everything that has come before. It's difficult to list points that the SPL PQ wouldn't fulfill or deliver to perfection.

Brilliant detailed solutions, extremely high-quality workmanship, and a sound that can only be described as "outstanding" in terms of flexibility and neutrality leave any doubter sitting mutely in the corner, unless they bring up the eternal topic of retail price.

As always in SPL's high-end range, it's simply pointless to discuss the price, as a true price/performance ratio cannot be established. The device has everything that triggers an official "aha" effect, visually and acoustically; more "showing off" is virtually impossible.

Here, everyone must decide for themselves whether the ultimate sound is worth a price beyond the 5,000 euro mark or not, period. One doesn't discuss with a Tesla driver whether the vehicle represents a real equivalent value for the purchase price.

The SPL PQ represents the pinnacle of analog equalizer design, offering uncompromising sound quality and flexibility for the most demanding mastering applications. Its hefty price tag will undoubtedly limit its accessibility to top-tier professional studios and well-heeled enthusiasts. However, for those who can justify the investment, the SPL PQ promises to be a powerful tool in the pursuit of sonic excellence, capable of imparting that elusive final polish to productions across all genres of music.

Ultimately, the value of the SPL PQ will be determined by the ears and workflows of the engineers who use it. In a world increasingly dominated by digital solutions, it stands as a testament to the enduring appeal of meticulously crafted analog equipment. Whether it becomes a new industry standard or remains a niche product for analog purists, the SPL PQ has undeniably raised the bar for what's possible in the realm of mastering equalizers.