Parametric EQ basics: filters, preamp, and clipping

A parametric equalizer changes tonal balance with a small set of precisely tuned filters. Each filter has three numbers: center frequency (where it acts), gain (how much boost or cut in dB), and Q (how narrow the effect is: higher Q, narrower band). Peaking filters handle bumps and dips; low-shelf and high-shelf filters tilt the whole bass or treble region.

Because tonal balance dominates how headphones sound, EQ is the rare free lunch: a $50 IEM equalized toward a well-fitting target genuinely competes tonally with far more expensive gear. It cannot fix distortion, seal, comfort, or add sub-bass extension a driver physically lacks. Pushing +10 dB at 20 Hz into a driver with no headroom just buys distortion.

The one rule you must not skip: any filter with positive gain requires a matching negative preamp (roughly minus the largest boost). Digital audio has no headroom above full scale, so a +6 dB boost on a loud passage clips and distorts unless the whole signal is first lowered by about 6 dB. Every preset exported from qfiAudio includes the correct preamp value.

Presets from oratory1990 (measured on industry-standard rigs, published as free PDFs) and the AutoEq project are the community standards, loaded into EqualizerAPO/Peace on Windows, Wavelet on Android, or the DSP in devices like the Qudelix 5K. A preset made from someone else's unit and rig is a starting point. Trust your ears for the last few dB, and adjust to taste.