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The SPL PQ follows the lineage of SPL devices built around the 120V philosophy, developed in the 1990s by Wolfgang Neumann, aiming to achieve technical performance and sonic ease difficult to obtain with more traditional topologies. This approach was initially designed for high-end mastering applications and has since become the foundation of the brand's premium products. In this spirit, the PQ has earned a reputation as a reference parametric equalizer: extensive control, wide dynamic range, and a sound that remains "open" even when finely sculpting the spectrum.
The PQ is designed for those who want highly controlled equalization on a stereo bus, mastering chain, stems, or even two independent mono sources. Its control logic (screens, per-band activation buttons, Q modes) encourages methodical work: compare, recall, adjust by tenths, without losing track. In the studio, it excels both at correcting a resonance and shaping a broad and coherent curve, with gain behavior that remains usable and musical.
Each channel has five fully parametric bands (LF, LMF, MF, MHF, HF). SPL intentionally designed a wide frequency overlap to allow treating a problematic area with two bands if necessary, or to distribute shaping more smoothly. The ranges are: 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.
Each band offers Cut/Boost up to +/-20 dB, useful for both targeted corrections and deliberate tonal choices. When only small adjustments are needed, the 1/4 Gain switch reduces the range to +/-5 dB: a real asset for working quickly, avoiding overly large gestures, and staying within a mastering mindset.
The blue button toggles the Q behavior. In Constant Q, amplitude remains stable regardless of bandwidth: this is the preferred mode for attenuating a problematic frequency with very predictable control. In Proportional Q, amplitude depends on bandwidth: the wider the band, the lower the maximum gain (up to about +/-2.8 dB at maximum width, and up to +/-20 dB at minimum width). This behavior helps achieve creative and sensitive equalizations, as large moves on wide curves naturally become more measured.
Each band can be activated or deactivated via the orange button, facilitating comparisons and progressive curve building. The PQ is a true dual mono: you can process two independent mono sources or a stereo left/right program. In Link mode, the On/Off controls for bands and the Constant/Proportional Q selection are linked between channels to speed up stereo work while maintaining the "mastering" philosophy of control and coherence.
For objective evaluation, the PQ offers an Auto Bypass: instead of manually switching between original and processed signals, the system automatically alternates at an adjustable interval. This allows you to stay centered at the listening position, better judge the real impact of the EQ, and avoid biases related to handling or slight movements during critical listening.
120V technology uses an internal voltage of +/-60 V and proprietary SUPRA operational amplifiers designed to support this architecture. The result targets both measurable performance (dynamic range, signal-to-noise ratio, headroom) and the listening experience: more detail, a more stable image, and equalization that holds up even when stacking multiple corrective actions.
