091HPDoctor
Key Features
- High-pass filtering range extends from 1 Hz to 150 Hz for subsonic cleanup below typical EQ cutoff limits.
- Slope choices run from 1 dB/oct to 24 dB/oct, with the available range depending on the selected filter model.
- Seven filter types cover Butterworth, Elliptic, Chebyshev I, Chebyshev II, Bessel, Ladder, and Allpass behavior.
- Optional Const -3 dB mode keeps cutoff behavior more consistent when comparing filter types.
- 64-bit double-precision internal processing supports clean utility work in mixing and mastering chains.
- Click-free transitions prevent parameter and filter-type changes from causing audible switching artifacts.
- Signed macOS build plus Windows and Linux downloads make the same low-frequency tool available across desktop systems.
Description
091HPDoctor is a precision high-pass filter from 091Audio built for low-frequency cleanup below the range most utility EQs expose. Instead of starting at 20 Hz, it reaches down to 1 Hz, making it useful for DC offset removal, subsonic rumble control, and low-end shaping that should not disturb the audible bass range.
The plugin covers 1-150 Hz with slopes from 1 dB/oct to 24 dB/oct depending on the selected filter type. Butterworth, Elliptic, Chebyshev I, Chebyshev II, Bessel, Ladder, and Allpass modes give you different phase and resonance behavior for corrective filtering, console-style roll-offs, and phase alignment work.
HPDoctor is intentionally narrow in scope, which is part of the appeal. The interface is clean, parameter changes are click-free, and the 64-bit double-precision internal processing makes it feel like a focused engineering tool rather than a broad character EQ.
Use it when a normal high-pass filter is too coarse for mastering cleanup, cinematic booms, kicks, basses, or compressor prep. The official macOS, Windows, and Linux downloads are direct and require no signup, so the hosted SSA mirrors use the original release files.
Frequently Asked Questions
What makes 091HPDoctor different from a normal high-pass filter?
Most high-pass filters begin around 20 Hz or make that area hard to adjust precisely. 091HPDoctor reaches down to 1 Hz and offers fine slope choices, so it can remove DC offset or subsonic energy without forcing a broad cut into the audible low end.
Why does the Allpass mode matter?
Allpass filtering changes phase without the same kind of amplitude cut you get from a standard high-pass filter. That makes it useful for low-frequency phase alignment experiments, especially around kicks, basses, layered impacts, or other sources where timing and phase relationships affect weight.
Is 091HPDoctor more of a mixing EQ or a mastering utility?
It can work in both roles, but it is best thought of as a narrow low-frequency utility rather than a full EQ. Use it before compressors, on low-end sound design, or in mastering cleanup when you need more control below 20 Hz.
Does 091HPDoctor require signup or account creation?
No. The official 091Audio page provides direct downloads for macOS, Windows, and Linux, and the page says the download is available with no signup needed.
