SPL PQ - Parametric EQ The SPL PQ is a dual-mono stereo mastering equaliser built around ten fully parametric filter bands, five per channel, and powered by SPL's proprietary 120V technology. Originally developed alongside the legendary SPL MMC1 Mastering Console for Galaxy Studios, the PQ has since established itself as one of the most respected and versatile parametric equalisers in professional mastering. Its combination of surgical precision and musical flexibility, delivered through a design that operates at ±60V internally, has earned it a loyal following among some of the world's most discerning mastering engineers. What makes the PQ genuinely distinctive is the ability to switch each of its ten filter bands independently between Constant Q and Proportional Q behaviour. In Constant Q mode, the amplitude remains fixed regardless of the selected bandwidth, ideal for isolating and eliminating problematic frequencies with accuracy. In Proportional Q mode, the amplitude scales with bandwidth: narrower settings produce higher gain, wider settings produce gentler, more diffuse curves that interact naturally with programme material. At the narrowest bandwidth the maximum cut/boost is ±20dB; at the widest setting this reduces to approximately ±2.8dB, providing an inherently musical taper that makes broad tonal shaping feel intuitive rather than clinical. Each filter band offers up to ±20dB of cut or boost, with an additional 1/4 Gain mode that reduces the effective range to ±5dB, useful when only the most delicate refinements are needed. All five frequency bands overlap generously across the spectrum (LF: 10Hz–330Hz; LMF: 33Hz–1kHz; MF: 128Hz–4.1kHz; MHF: 310Hz–10.2kHz; HF: 760Hz–24kHz), allowing adjacent bands to address the same frequency from different angles and giving the engineer complete control over the shape of any correction or enhancement. The centre section introduces two particularly practical features. Auto Bypass allows the unit to switch automatically between the processed and bypassed signal at an adjustable interval, removing the engineer from the stereo centre during comparison and enabling a more objective evaluation without the distraction of manual switching. The Link function joins both channel strips together so that activating or changing a filter band's mode on one side simultaneously affects the other, essential for stereo mastering work where consistency between left and right must be maintained. Uniquely, the controlling channel can be reassigned to either side, allowing the workflow to be adapted to personal preference. All controls are implemented with 41-step detented potentiometers, giving the PQ excellent recall accuracy across both channels, a critical requirement in professional mastering environments. The 120V technology at the heart of the PQ operates at ±60V internally via SPL's proprietary SUPRA operational amplifiers. Where most audio devices work at ±15V and clip at around +21.5dBu, the PQ handles input and output levels up to +32.5dBu, giving it 12dB more headroom. At these operating conditions all components function comfortably within their optimal range, contributing to the notably low THD figure of 0.0005% and a dynamic range of 135dB. The result is an equaliser that is both technically exemplary and sonically transparent: rich in detail, free from harshness, and exceptionally easy to work with over long sessions. Power is provided by an internal linear supply with a shielded toroidal transformer, and the unit is manufactured entirely at SPL's facility in Niederkrüchten, Germany. SPL PQ Key Features: Dual-mono stereo mastering parametric equalizer, processing two independent mono signals simultaneously or a stereo left/right programme 10 fully parametric filter bands, 5 per channel (LF, LMF, MF, MHF, HF) Each band independently switchable between Constant Q and Proportional Q mode Constant Q: fixed amplitude regardless of bandwidth, ideal for problem frequency removal Proportional Q: amplitude scales with bandwidth (±20dB at narrowest; ±2.8dB at widest) for musical, natural tonal shaping Cut/boost range of ±20dB per band; 1/4 Gain switch reduces range to ±5dB for fine adjustments Generous frequency overlap between bands: LF 10Hz–330Hz / LMF 33Hz–1kHz / MF 128Hz–4.1kHz / MHF 310Hz–10.2kHz / HF 760Hz–24kHz Auto Bypass function with adjustable switching interval for objective A/B comparison without manual intervention Link mode joins controls across both channels simultaneously; controlling channel assignable to either side Individual On/Off switching per band and per channel All controls implemented with 41-step detented potentiometers for reliable recall SPL 120V technology operating at ±60V internally via proprietary SUPRA op-amps +32.5dBu maximum input/output level, giving 12dB more headroom than standard ±15V designs 135dB dynamic range; THD 0.0005% at +30dBu Internal linear power supply with shielded toroidal transformer Electronically balanced XLR inputs and outputs Manufactured in Niederkrüchten, Germany SPL PQ Specifications: Analogue Inputs & Outputs (XLR balanced) Maximum Input/Output Level: 32.5 dBu Input Impedance: 20 kΩ Output Impedance: 75 Ω Common Mode Rejection: -82 dBu Frequency Range (-3dB): 10 Hz – 100 kHz THD & N (+30dBu, 1kHz): 0.0005% Noise (A-weighted): -94.3 dBu Dynamic Range: 135 dB Power Supply Internal operating voltage (audio): ±60V DC Relay/LED voltage: +12V DC Mains: 230V AC / 50Hz or 115V AC / 60Hz (selectable) Fuse (230V): T 3.15A; Fuse (115V): T 6.3A Power consumption: max. 100 VA Physical Dimensions (W x H x D): 482 x 177 x 300 mm / 19 x 6.97 x 11.8 inches Unit weight: 15.2 kg / 33.51 lbs Shipping weight (inc. packaging): 17.8 kg / 39.24 lbs
