091HPDoctor

091HPDoctor is a precision high-pass filtering utility built for situations where conventional HPFs fall short. Extending the cutoff range down to 1 Hz, it enables surgical control of subsonic content, DC offset, and low-frequency buildup without compromising the audible bass range. Featuring seven distinct filter types—including Butterworth, Elliptic, Chebyshev I & II, Bessel, Ladder, and Allpass—HPDoctor provides a wide palette of tonal and phase responses. Fractional slope settings from 1 dB/oct up to 24 dB/oct allow for subtle console-style filtering, transparent mastering cleanup, or more aggressive low-end shaping with resonant character. The dedicated Allpass mode adds powerful phase manipulation and alignment capabilities, while the optional Const -3 dB mode ensures consistent cutoff behavior across filter designs. With double-precision internal processing and click-free parameter transitions, HPDoctor delivers accurate, artifact-free low-frequency control for mixing, mastering, sound design, and restoration workflows.