PQ

Mastering Equalizer

This is a unique equalizer – for several reasons. It has two times five fully parametric filter bands, each of which can be switched between constant Q and proportional Q! And there’s sheer unlimited headroom and a very special kind of EQ sound – thanks to 120V technology.

The Filter Bands

Stepped Potentiometers

Recall of all settings is easy thanks to the potentiometers with 41 steps.

Cut/Boost & 1/4 Gain

Each filter band can be boosted or cut up to 20 dB.

If only minimal changes are required, the 1/4 Gain switch can be used to reduce the boost or cut range from +/-20 dB to +/-5 dB.

Frequencies

We have designed the frequency distribution to overlap widely between the bands, so that problematic frequencies can also be addressed with two bands.

LF	10 Hz – 330 Hz
LMF	33 Hz – 1 kHz
MF	128 Hz – 4.1 kHz
MHF	310 Hz – 10.2 kHz
HF	760 Hz – 24 kHz

Bandwidth Q

The bandwidth Q determines the steepness of bell characteristic. A small Q is a wide bandwidth and a high Q a narrow bandwidth.

The labeling of the scale is divided into two parts. The values with white background refer to the proportional Q mode and the values without background refer to the constant Q mode.

Constant & Proportional Q

The blue button is used to toggle the Q mode.

In constant Q mode, the amplitude is constant regardless of the selected bandwidth. This is ideal for eliminating interfering frequencies.

In proportional Q mode, the amplitude is proportional to the bandwidth. It decreases with increasing bandwidth and vice versa. At the smallest bandwidth setting, the maximum amplitude value is +/- 20 dB, while the maximum amplitude decreases to +/- 2.8 dB at the largest bandwidth setting. This control behavior simplifies sensitive, creative processing and is musically very useful, since high amplitudes become increasingly unusable with increasing bandwidth.

On/Off

The orange button is used to switch the individual filter band on and off.

The Center Section

Auto Bypass

For an objective evaluation of the edited music program, it makes sense not to switch between the original signal and the edited signal yourself, but to leave this to an automatic system.

 

It is also an advantage that, for an optimal evaluation of the processing, one does not have to move from the stereo center and can concentrate fully on the program.

 

With the help of the Interval control the switching time window can be determined. Turning it clockwise extends the time interval.

 

The 120V technology

The 120V technology is our reference technology. The 120V technology is unique in the world. It operates at a DC voltage of 120 volts. This is four times that of IC-based semiconductor op-amps.

The highest possible audio quality requires the highest possible audio operating voltage.

The 120V technology works with +/-60 V. To be able to handle such a high voltage, we have developed special proprietary operational amplifiers that can operate with a DC voltage of +/-60 V: the SPL 120V SUPRA operational amplifiers.

This high voltage would destroy conventional components and operational amplifiers.

 

The 120V technology achieves exceptional technical specifications and sonic benefits. Technically, in terms of dynamic range, signal-to-noise ratio and headroom. Sonically, in terms of richness of detail and an absolutely relaxed listening experience.

By the way, the “120V” in the name of the technology has nothing to do with the local mains voltage from the mains power socket. This is about the operating voltage inside the device with which the audio signals are processed.

The mains voltage from the mains power socket is transformed to the required secondary voltage in the device’s internal linear power supply with toroidal transformer. Rectifiers convert this AC voltage into DC voltage required in the audio device.

The idea for SPL 120V technology and the SUPRA operational amplifier based on this technology were developed in the 1990s by SPL founder and chief developer Wolfgang Neumann.

 

With the goal of building the best mastering console ever, this basic technological philosophy then took shape for the first time – thus the SPL MMC1 Mastering Console for Galaxy Studios saw the light of day in 2000.

The outstanding sonic and technical features quickly got around in the scene – so further orders were not long in coming.

Besides the MMC 1, another legendary product with 120V technology was created with the PQ, the “King of Parametric Equalizers”.

Since that time, 120V technology has been the foundation for all SPL premium products. Meanwhile, not only for mastering applications, but also for the, studio or hifi use.

 

Comparison

Most audio devices work with an internal operating voltage of +/-15 volts and can thus process a maximum input level of +21.5 dBu. If a DAC, for example, has an output level of +22 dBu at 0 dBFS, level peaks of the music material would already cause overloads in the input stage of the device.

 

All components in the audio device often operate at their limits. The result is an unsteady sound that causes stress and faster ear fatigue.

SPL devices with 120V technology can handle input levels of +32.5 dBu thanks to the higher internal operating voltage of +/- 60 volts – thus offering 12 dB more headroom. All components consequently operate continuously in the optimum operating range. The result is a very pleasant, natural and relaxed sound experience. So you can enjoy your music in every detail.

 

These diagrams clearly show the superiority of the 120V technology in comparison to other circuits with lower, common operating voltages.

For audio professionals and mastering engineers, achieving pristine sound quality with precise control over tonal balance is paramount. The SPL Audio PQ Mastering Equalizer is designed to meet the exacting demands of studio environments where clarity, accuracy, and subtlety define the final product. This mastering equalizer offers a sophisticated analog solution that enables you to shape your audio with unparalleled precision, ensuring your mixes translate perfectly across all playback systems.

Many mastering equalizers introduce unwanted noise or color the sound in ways that detract from the original recording. The SPL Audio PQ Mastering Equalizer addresses these issues by combining a wide frequency range with exceptionally low distortion and noise. With a frequency response spanning from 10 Hz to 100 kHz at -3 dB, it covers the entire audible spectrum and beyond, preserving the integrity of high-frequency content that is often lost or degraded by lesser units. This means you can sculpt your tracks without sacrificing detail or introducing artificial artifacts.

One of the standout features of this equalizer is its analog input and output stage, which supports a maximum gain of 32.5 dBu. This high gain capability ensures compatibility with professional studio equipment and maintains signal integrity even at elevated levels. The input impedance of 20 kΩ and output impedance of 75 Ω guarantee optimal interfacing with a wide range of studio gear, minimizing signal loss and ensuring a clean, transparent sound. The common mode rejection of -82 dBu further reduces noise interference, providing a pure signal path essential for critical listening environments.

The unit prides itself on its extremely low total harmonic distortion plus noise (THD+N) of just 0.0005% at +30 dBu and 1 kHz. For the customer, this translates to an equalizer that imparts no unwanted coloration or distortion, preserving the original character of your audio. Furthermore, the noise floor is impressively low at -94.3 dBu (A-weighted), coupled with an extraordinary dynamic range of 135 dB. Together, these specifications mean that your audio remains clean and dynamic, even when subtle adjustments are made, allowing for delicate tonal shaping without compromising fidelity.

In practical terms, the SPL PQ Mastering Equalizer is built for reliable operation in professional studios. It supports selectable mains voltage options of 230 V AC at 50 Hz or 115 V AC at 60 Hz, enabling use in various regions worldwide. The power consumption peaks at 100 VA, making it energy-efficient for continuous studio use. Physically, the unit measures 482 mm wide, 177 mm high, and 300 mm deep (19 x 6.97 x 11.8 inches), fitting standard 19-inch rack setups while weighing 17.8 kilograms (39.24 pounds), which ensures a solid, durable build that remains stable during operation.

This mastering equalizer is ideal for audio professionals engaged in mixing, mastering, and critical listening, where precision and reliability are non-negotiable. Whether you are refining a final stereo master or working on complex multitrack mixes, the SPL PQ Mastering Equalizer allows you to achieve the tonal balance you envision, contributing to professional-grade productions that stand out in clarity and impact.

Investing in the SPL Audio PQ Mastering Equalizer means choosing a tool that elevates your mastering workflow by providing transparent, high-fidelity sound shaping with robust analog engineering. Backed by meticulous design and premium components, this equalizer inspires confidence in your sound decisions, ensuring your audio projects reach their full sonic potential. With this unit in your studio, you can trust that every frequency adjustment enhances your work, bringing your creative vision to life with unmatched precision.