VoidFilter

A stable highpass/lowpass/bandpass filter VST plugin built with JUCE, featuring smooth parameter automation, zero-delay feedback (ZDF) state variable filter topology, and professional-grade stability guarantees.

Link to the VST

https://github.com/michaellwatson/voidfilter/raw/refs/heads/main/build/VoidFilter_artefacts/Release/VST3/VoidFilter.vst3/Contents/x86_64-win/VoidFilter.vst3

Features

• Three Filter Modes: Lowpass, Highpass, and Bandpass
• Smooth Parameter Automation: One-pole smoothing prevents zipper noise during automation
• Stable at Any Setting: Zero-Delay Feedback (ZDF) State Variable Filter topology ensures stability at extreme resonance and cutoff values
• Sample Rate Agnostic: Properly handles 44.1kHz, 48kHz, 96kHz, and other sample rates
• Low CPU Usage: Optimized DSP implementation with denormal protection
• Modern GUI: Clean, responsive interface with real-time value display

Technical Details

Filter Topology

VoidFilter uses a TPT (Topology Preserving Transform) State Variable Filter based on Vadim Zavalishin's Zero-Delay Feedback method. This provides:

• Stable operation at any resonance level (no filter blow-ups)
• Accurate frequency response at all sample rates
• Linear behavior suitable for real-time modulation

Stability Features

• Parameter Clamping: Cutoff (20 Hz - 20 kHz) and Resonance (0.0 - 10.0) are automatically clamped
• Denormal Protection: Uses juce::ScopedNoDenormals to prevent CPU spikes
• Smooth Automation: 50ms time-constant smoothing for cutoff and resonance parameters
• Per-Sample Coefficient Updates: Ensures smooth parameter changes without artifacts

Building

Prerequisites

• CMake 3.22 or higher
• C++17 compatible compiler
• JUCE 7.0+ (will be automatically downloaded if not specified)

Build Instructions

1. Clone the repository:

   git clone <repository-url>
   cd voidfilter

2. Create build directory:

   mkdir build
   cd build

3. Configure with CMake:

   Option A - Let CMake download JUCE automatically:

   cmake ..

   Option B - Use your local JUCE installation:

   cmake -DJUCE_ROOT=/path/to/JUCE ..

4. Build the plugin:

   Windows (Visual Studio):

   cmake --build . --config Release

   macOS/Linux:

   cmake --build . --config Release -j

5. Plugin Location:

   • Windows: build/VoidFilter_artefacts/Release/VST3/VoidFilter.vst3
   • macOS: build/VoidFilter_artefacts/Release/VST3/VoidFilter.vst3
   • Linux: build/VoidFilter_artefacts/Release/VST3/VoidFilter.vst3

Installation

1. Copy the .vst3 file to your VST3 plugin directory:

   • Windows: C:\Program Files\Common Files\VST3\
   • macOS: ~/Library/Audio/Plug-Ins/VST3/
   • Linux: ~/.vst3/ or /usr/local/lib/vst3/

2. Rescan plugins in your DAW

Usage

Parameters

• Cutoff: Frequency in Hz (20 - 20,000 Hz)

  • Logarithmic scale for natural frequency sweep feel
  • Smoothly automatable without zipper noise

• Resonance: Q factor (0.0 - 10.0)

  • Higher values create a resonant peak at the cutoff frequency
  • Stable at maximum values

• Mode: Filter type

  • Lowpass: Passes frequencies below cutoff, attenuates above
  • Highpass: Passes frequencies above cutoff, attenuates below
  • Bandpass: Passes frequencies around the cutoff, attenuates others

Tips

• The filter is designed to be stable even with rapid automation
• High resonance values create a pronounced peak - use gain compensation if needed
• The logarithmic cutoff scale makes it easier to sweep musically relevant frequency ranges

Architecture

voidfilter/
├── CMakeLists.txt              # CMake build configuration
├── Source/
│   ├── FilterDSP.h            # TPT SVF filter implementation
│   ├── PluginProcessor.h      # AudioProcessor with parameter management
│   ├── PluginProcessor.cpp    # Audio processing and smoothing
│   ├── PluginEditor.h         # GUI component
│   └── PluginEditor.cpp       # GUI implementation with throttled repaint
├── README.md                  # This file
└── LICENSE                    # MIT License

Testing Recommendations

When testing the plugin, verify:

• Sample Rates: Test at 44.1kHz, 48kHz, and 96kHz - filter behavior should remain consistent
• Edge Cases:
  • Minimum cutoff (20 Hz)
  • Maximum cutoff (20 kHz)
  • Maximum resonance (10.0)
• Automation: Rapid parameter changes should be smooth without artifacts
• Stability: No filter blow-ups or NaN/Inf values even with extreme settings

Known Limitations

• Currently supports VST3 format only (Standalone also available)
• No oversampling (can be added for future enhancement)
• No soft saturation/warmth controls (planned for future release)

Future Enhancements

Potential additions for future versions:

• Soft saturation/tanh distortion for analog warmth
• Oversampling for improved high-resonance quality
• Additional filter modes (notch, allpass)
• Visual frequency response display
• Drive and dry/wet controls

License

MIT License - see LICENSE file for details

Credits

• Filter design based on Vadim Zavalishin's Zero-Delay Feedback method
• Built with JUCE Framework

Troubleshooting

Plugin doesn't appear in DAW:

• Ensure the .vst3 file is in the correct VST3 directory
• Rescan plugins in your DAW
• Check that the plugin was built for the correct architecture (64-bit)

Filter sounds unstable:

• This should not happen with the ZDF implementation, but if it does:
  • Check sample rate (should be > 0)
  • Verify parameters are within valid ranges
  • Report as a bug with your system specifications

High CPU usage:

• Denormal protection should prevent this
• If experiencing issues, check that compiler optimizations are enabled