Trilophilter LV2 Plugin

Three-band filter plugin with independent high-pass, mid-band, and low-pass filters, designed for low CPU usage. The high and low filters offer multiple slope options for Classic, Butterworth and Linkwitz-Riley responses, while the mid-band filter features Bell and Notch modes for precise frequency shaping.

Plugin controls as displayed by Ardour's default generic UI. Your host may show controls differently. The frequency analysis graph shown below the controls is part of Ardour's plugin window, not a feature of this plugin.

Features

• Independent high-pass, mid-band, and low-pass filters
• Multiple slope options for the high and low filters :
  • Off (filter bypassed)
  • Classic -12dB/octave
  • Classic -24dB/octave
  • Butterworth -24dB/octave
  • Butterworth -48dB/octave
  • Linkwitz-Riley -48dB/octave
  • Linkwitz-Riley -96dB/octave
  • Low-Shelf (with adjustable Gain)
  • High-Shelf (with adjustable Gain)
• Mid-band filter slope options :
  • Bell (with adjustable Gain)
  • Notch
• Adjustable cutoff frequency (20Hz-20kHz) for all three filters
• Resonance/Q control for Classic modes, Shelves, Bell and Notch slopes
• Gain control (-12dB to +12dB) for Shelf and Bell filters
• Butterworth and Linkwitz-Riley modes ignore resonance
• No custom GUI — uses host's generic controls
• Stereo input/output
• No dependencies beyond LV2 SDK

Project Home

https://simdott.github.io/trilophilter

Plugin URI

urn:simdott:trilophilter

Dependencies

• C compiler (gcc, clang, etc.)
• LV2 development headers

Installation by distribution

Debian/Ubuntu : sudo apt-get install build-essential lv2-dev

Fedora : sudo dnf install gcc lv2-devel

Arch : sudo pacman -S base-devel lv2

Build and Install

1. Download the source : git clone https://github.com/simdott/trilophilter cd trilophilter

2. Install for current user (recommended) : sh install.sh

   Or install system-wide (requires sudo) : sudo sh install.sh

Verification

List installed plugins : lv2ls | grep trilophilter

Should show : urn:simdott:trilophilter

Usage

Load in any LV2-compatible host (Ardour, Carla, Reaper, etc.). Connect stereo inputs/outputs.

Each filter operates independently :

• High-Pass Filter (HPF) : Use Slope, Cutoff, and Q controls to shape the low end
• Mid-Band Filter (MBF) : Use Slope, Cutoff, and Q controls to shape the mid band
• Low-Pass Filter (LPF) : Use Slope, Cutoff, and Q controls to shape the high end

Classic modes : Resonance (Q) shapes the filter's response at the cutoff frequency :

• Low Q values (<50%) : Gentle, broad filter
• 50% : Standard flat response (Q=0.707)
• High Q values (>50%) : Resonant peak, more pronounced as Q increases

Butterworth modes : Provide flat passband response. Individual low-pass and high-pass outputs are -3dB at cutoff. Q control has no effect in these modes.

Linkwitz-Riley modes : Provide flat summed response for crossover applications. Individual low-pass and high-pass outputs are -6dB at cutoff. Q control has no effect.

High-Shelf/Low-Shelf :

• Low-Shelf : Boosts/cuts below cutoff frequency
• High-Shelf : Boosts/cuts above cutoff frequency
• Cutoff : Transition frequency
• Gain : Amount of boost/cut (-12dB to +12dB)
• Q (Resonance) : Steepness of the shelf transition (0% to 100%)
  • 0% = Very gentle slope (Q=0.3)
  • 50% = Classic Butterworth slope (default - Q=0.707)
  • 100% = Steep, aggressive slope (Q=1.5)

Bell mode :

• Bell : Boosts or cuts a specific frequency range
• Cutoff : Center frequency of the bell curve
• Gain : Amount of boost/cut (-12dB to +12dB)
• Q (Resonance) : Width of the bell curve (0% to 100%)
  • 0% = Very wide, extremely gentle curve (Q=0.2)
  • 50% = Moderate width, versatile for mixing (default - Q=3.0)
  • 100% = Very narrow, surgical cut or boost (Q=10.0)

Notch mode :

• Notch : Removes or attenuates a specific frequency range
• Cutoff : Center frequency of the notch
• Gain : Has no effect in Notch mode
• Resonance (Q) : Width of the notch (0% to 100%)
  • 0% = Wide notch, affects broader frequency range (Q=0.5)
  • 50% = Medium notch, good for general problem removal (default - Q=2.0)
  • 100% = Narrow notch, precise frequency removal (Q=8.0)
• Note : Unlike Bell mode, Notch only cuts (attenuates) frequencies and does not boost

To bypass a filter : Set its Slope control to "Off".

Interface : this plugin has no custom graphical interface. It uses your host's standard control UI (slider, knob, or numerical entry).

Note for Carla Users : the cutoff frequency and the resonance/Q controls use the LV2 pprops:logarithmic hint for logarithmic scaling. This works in Ardour and most hosts, but Carla currently displays these controls linearly. This is a host implementation difference, not a plugin issue. If precise logarithmic control in Carla is important to you, please let me know by opening an issue — this helps me prioritize a custom GUI in the future.

Technical Notes

All filters implemented as IIR biquad cascades. Designed for minimal CPU usage (no oversampling and phase response is non-linear) while providing versatile filter options. Aliasing may occur near Nyquist with high cutoff frequencies.

Files

• trilophilter.c - Plugin source code
• trilophilter.ttl - Plugin description (ports, properties)
• manifest.ttl - Bundle manifest
• install.sh - Build and install script
• uninstall.sh - Uninstall script

Uninstall

1. Open a terminal in the plugin's folder.

2. Uninstall for current user : sh uninstall.sh

   Or uninstall system-wide : sudo sh uninstall.sh

Latest Version

• v1.0.0 (2026-05-25) - Initial release

License

GPL-2.0-or-later

Author

Simon Delaruotte (simdott)