State Variable Filter

A low, band, and high pass filter with cutoff and resonance controls.
dsp::StateVariableTPTFilter
Switching filter type from the UI
AudioBlock processing
Source: examples/DSP/StateVariableFilterDemo.h on GitHub.
StateVariableFilterDemo.h
cpp
/*******************************************************************************
 The block below describes the properties of this PIP. A PIP is a short snippet
 of code that can be read by the Projucer and used to generate a JUCE project.

 BEGIN_JUCE_PIP_METADATA

 name:             StateVariableFilterDemo
 version:          1.0.0
 vendor:           JUCE
 website:          http://juce.com
 description:      State variable filter demo using the DSP module.

 dependencies:     juce_audio_basics, juce_audio_devices, juce_audio_formats,
                   juce_audio_processors, juce_audio_utils, juce_core,
                   juce_data_structures, juce_dsp, juce_events, juce_graphics,
                   juce_gui_basics, juce_gui_extra, juce_audio_processors_headless
 exporters:        xcode_mac, vs2022, vs2026, linux_make

 moduleFlags:      JUCE_STRICT_REFCOUNTEDPOINTER=1

 type:             Component
 mainClass:        StateVariableFilterDemo

 useLocalCopy:     1

 END_JUCE_PIP_METADATA

*******************************************************************************/

#pragma once

#include "../Assets/DemoUtilities.h"
#include "../Assets/DSPDemos_Common.h"

using namespace dsp;

//==============================================================================
struct StateVariableFilterDemoDSP
{
    void prepare (const ProcessSpec& spec)
    {
        sampleRate = spec.sampleRate;
        filter.prepare (spec);
    }

    void process (const ProcessContextReplacing<float>& context)
    {
        filter.process (context);
    }

    void reset()
    {
        filter.reset();
    }

    void updateParameters()
    {
        if (! approximatelyEqual (sampleRate, 0.0))
        {
            filter.setCutoffFrequency (static_cast<float> (cutoffParam.getCurrentValue()));
            filter.setResonance       (static_cast<float> (qParam.getCurrentValue()));

            switch (typeParam.getCurrentSelectedID() - 1)
            {
                case 0:   filter.setType (StateVariableTPTFilterType::lowpass);  break;
                case 1:   filter.setType (StateVariableTPTFilterType::bandpass); break;
                case 2:   filter.setType (StateVariableTPTFilterType::highpass); break;
                default:  jassertfalse;                                                   break;
            };
        }
    }

    //==============================================================================
    StateVariableTPTFilter<float> filter;

    ChoiceParameter typeParam {{ "Low-pass", "Band-pass", "High-pass" }, 1, "Type" };
    SliderParameter cutoffParam {{ 20.0, 20000.0 }, 0.5, 440.0f, "Cutoff", "Hz" };
    SliderParameter qParam {{ 0.3, 20.0 }, 0.5, 1.0 / MathConstants<double>::sqrt2, "Resonance" };

    std::vector<DSPDemoParameterBase*> parameters { &typeParam, &cutoffParam, &qParam };
    double sampleRate = 0.0;
};

struct StateVariableFilterDemo final : public Component
{
    StateVariableFilterDemo()
    {
        addAndMakeVisible (fileReaderComponent);
        setSize (750, 500);
    }

    void resized() override
    {
        fileReaderComponent.setBounds (getLocalBounds());
    }

    AudioFileReaderComponent<StateVariableFilterDemoDSP> fileReaderComponent;
};
State Variable Filter ​

State Variable Filter
