SplineEQ: Linear Phase Spline-Based Equalizer by Photosounder

Linear phase equalizers change only the intensity of frequencies and leave their phase untouched. Photosounder notes that this can produce better sound quality than common minimum phase equalizers, and that linear phase processing avoids aliasing artefacts.

SplineEQ builds each filter from a spline curve that can take almost any shape. A dashed curve shows the actual filter response whenever it differs from the ideal spline, and the filter resolution can be adjusted.

You can use between 1 and 60 bands, and the free version is limited to 4. Double-clicking the visualisation area creates or disables a band, and bands can be adjusted there, with the knobs, or with automatable parameter sliders in the host.

Curve tools include transposing the curve by up to 10 octaves, shifting all gains together, and scaling gains by a ratio to flatten, exaggerate or reverse a curve. The frequency analyser shows spectrum intensity before and after filtering in colour, at a resolution of about 10 Hz. The gain range runs from -60 dB to +60 dB, with a built-in limiter for boosts.