091Audio is giving away 091HPDoctor, a high-precision high-pass filter plugin, for free. The offer is ending soon, so grab it while it is available. This post covers the download details and an overview of 091HPDoctor.
What Is 091Audio 091HPDoctor?
091HPDoctor is a high-pass filter plugin built for precise control of the low end between 1 Hz and 150 Hz. Typical high-pass filters only go down to 20 Hz and offer limited slope and filter-type options. HPDoctor reaches down to 1 Hz, with fractional slopes from 1 dB/oct to 24 dB/oct and seven filter types.
Key Features
- Frequency range: 1 Hz to 150 Hz
- Slope: fractional slopes from 1 dB/oct to 24 dB/oct (depending on filter type)
- Seven filter types: Butterworth / Elliptic / Chebyshev I / Chebyshev II / Bessel / Ladder / Allpass
- Includes a “Const -3dB” mode
- Use cases: DC offset removal, cleaning up subsonic energy before compression, shaping resonance around the cutoff on kick and bass, console-style high-pass emulation, precise cleanup during mastering, and phase manipulation or alignment with Allpass mode
How to Download and Install 091HPDoctor
091HPDoctor can be downloaded and installed easily by choosing the installer for your operating system.
That is everything on the free release of 091HPDoctor. If you work with low-end-heavy material such as kick, bass, or mastering, it is well worth adding to your toolkit.

