wip: State Variable Filter (FILTER LFO WORKS NOW!!!)

inc/LFO.h

@@ -11,10 +11,3 @@ public:
     void SetFreq(float freq) { m_phase_dt = (this->*m_dt_function)(freq); }
 };
 
-LFO::LFO(/* args */): Oscillator(Sine, 0.f, 0.5f)
-{
-}
-
-LFO::~LFO()
-{
-}

inc/LowPassStateVariableFilter.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include "StateVariableFilter.h"
+
+class LowPassStateVariableFilter : StateVariableFilter {
+  protected:
+    float GetSampleForFilterType() override;
+
+  public:
+    LowPassStateVariableFilter();
+    LowPassStateVariableFilter(StateVariableFilter* filter);
+    LowPassStateVariableFilter(float freq, float res, float q);
+    ~LowPassStateVariableFilter();
+    bool IsSameFilterType(FilterType type) override { return type == LowPass; };
+};

inc/StateVariableFilter.h

@@ -0,0 +1,35 @@
+#pragma once
+#include "Filter.h"
+#include "IEffect.h"
+#include "Settings.h"
+
+class StateVariableFilter : public IEffect {
+  protected:
+    // float* m_output; // output buffer
+    float m_fs = SAMPLE_RATE; // sampling frequency;
+    float m_fc;    // cutoff frequency normally something like: 440.0*pow(2.0,
+                   // (midi_note - 69.0)/12.0);
+    float m_res;   // resonance 0 to 1;
+    float m_drive; // internal distortion 0 to 0.1
+    float m_freq;  
+    float m_damp; 
+    float m_notcho; // notch output
+    float m_lowo;   // low pass output
+    float m_higho;  // high pass output
+    float m_bando;  // band pass output
+    float m_peako;  // peaking output = low - high
+    virtual float GetSampleForFilterType(){ return 0.0; };
+
+  public:
+    StateVariableFilter(/* args */);
+    virtual ~StateVariableFilter();
+    void Trigger() override final;
+    void Release() override final;
+    float Process(float in);
+    void Process(std::vector<float>& samples) override final;
+    void SetParameters(float freq, float res, float drive);
+    float GetFreq() { return m_fc; }
+    float GetRes() { return m_res; }
+    float GetPeakGain() { return m_drive; }
+    virtual bool IsSameFilterType(FilterType type) { return false; };
+};

inc/Synth.h

@@ -1,13 +1,14 @@
 #pragma once
 
 #include "ADSR.h"
-#include "Filter.h"
+#include "StateVariableFilter.h"
 #include "Adder.h"
 #include "IEffect.h"
 #include "Note.h"
 #include "Oscillator.h"
 #include "Settings.h"
 #include <vector>
+#include "LFO.h"
 
 class Synth {
   private:
@@ -15,7 +16,7 @@ class Synth {
     std::vector<Oscillator*> m_oscillators;
     std::vector<IEffect*> m_effects;
     std::vector<float> m_out_signal;
-    Oscillator* m_lfo;
+    LFO* m_lfo;
     void ZeroSignal();
     void GetNote();
     void TriggerNoteOnEffects();
@@ -34,6 +35,6 @@ class Synth {
     const std::vector<Oscillator*>& GetOscillators() { return m_oscillators; }
     const bool& GetIsNoteTriggered() { return is_note_triggered; }
     ADSR* GetADSR() { return (ADSR*)m_effects[0]; }
-    Filter* GetFilter() { return (Filter*)m_effects[1]; }
+    StateVariableFilter* GetFilter() { return (StateVariableFilter*)m_effects[1]; }
     void SetFilter(FilterType type);
 };

src/LFO.cpp

@@ -0,0 +1,10 @@
+#include "LFO.h"
+
+
+LFO::LFO(/* args */): Oscillator(Sine, 0.f, 0.5f)
+{
+}
+
+LFO::~LFO()
+{
+}

src/LowPassFilter.cpp

@@ -4,7 +4,7 @@
 LowPassFilter::LowPassFilter() {
     // todo: defaults
     m_freq = 200.f / SAMPLE_RATE;
-    m_q = 1.0f;//0.707f;
+    m_q = 0.707f;//0.707f;
     m_order = 0;
 }
 

src/LowPassStateVariableFilter.cpp

@@ -0,0 +1,21 @@
+#include "LowPassStateVariableFilter.h"
+
+LowPassStateVariableFilter::LowPassStateVariableFilter() {
+    SetParameters(200, 0.1, 0.001);
+}
+
+LowPassStateVariableFilter::LowPassStateVariableFilter(
+    StateVariableFilter* filter) {
+    SetParameters(filter->GetFreq(), filter->GetRes(), filter->GetPeakGain());
+}
+
+LowPassStateVariableFilter::LowPassStateVariableFilter(float freq, float res,
+                                                       float q) {
+    SetParameters(freq, res, q);
+}
+
+LowPassStateVariableFilter::~LowPassStateVariableFilter() {}
+
+float LowPassStateVariableFilter::GetSampleForFilterType() {
+    return m_lowo;
+}

src/Renderer.cpp

@@ -203,7 +203,7 @@ void Renderer::draw_second_panel(Rectangle& bounds) {
 float Renderer::DrawFilterPanel(Synth& synth, FilterGuiState& gui_filter,
                                 const Rectangle& panel_bounds) {
 #define FILTER_TYPE_OPTIONS "LP;BP;HP"
-    Filter* filter = synth.GetFilter();
+    StateVariableFilter* filter = synth.GetFilter();
     float panel_y_offset = 0;
 
     // Draw Filter Panel
@@ -257,6 +257,10 @@ float Renderer::DrawFilterPanel(Synth& synth, FilterGuiState& gui_filter,
     // apply values to real one
     // todo: thrid (order) parameter
     // todo: why resonance changing does not work?
+    // todo: limit statevariablefilter lowest frequency  to ~40 hz
+    if (gui_filter.freq < 40.0) {
+        gui_filter.freq = 50.0;
+    }
     filter->SetParameters(gui_filter.freq, filter->GetRes(),
                           filter->GetPeakGain());
 

src/StateVariableFilter.cpp

@@ -0,0 +1,50 @@
+#include "StateVariableFilter.h"
+#include "Settings.h"
+#include <algorithm>
+#include <cmath>
+
+StateVariableFilter::StateVariableFilter(/* args */) {}
+
+StateVariableFilter::~StateVariableFilter() {}
+
+void StateVariableFilter::Trigger() {}
+
+void StateVariableFilter::Release() {}
+
+void StateVariableFilter::Process(std::vector<float>& samples) {
+    for (std::size_t i = 0; i < samples.size(); i++) {
+        samples[i] = Process(samples[i]);
+    }
+}
+
+
+float StateVariableFilter::Process(float in) {
+    m_notcho = in - m_damp * m_bando;
+    m_lowo = m_lowo + m_freq * m_bando;
+    m_higho = m_notcho - m_lowo;
+    m_bando =
+        m_freq * m_higho + m_bando - m_drive * m_bando * m_bando * m_bando;
+    // (m_notcho or m_lowo or m_higho or m_bando or m_peako)
+    float out = 0.5 * GetSampleForFilterType();
+    m_notcho = in - m_damp * m_bando;
+    m_lowo = m_lowo + m_freq * m_bando;
+    m_higho = m_notcho - m_lowo;
+    m_bando =
+        m_freq * m_higho + m_bando - m_drive * m_bando * m_bando * m_bando;
+    out += 0.5 * GetSampleForFilterType();
+
+    return out;
+}
+
+void StateVariableFilter::SetParameters(float freq, float res, float drive) {
+    m_fc = freq;
+    m_res = res;
+    m_drive = drive;
+
+    // the fs*2 is because it's double sampled
+    m_freq =
+        2.0 * std::sinf(SYNTH_PI * std::min(0.25f, m_fc / (m_fs * 2)));
+
+    m_damp = std::min(2.0f * (1.0f - std::powf(m_res, 0.25f)),
+                            std::min(2.0f, 2.0f / m_freq - m_freq * 0.5f));
+}

src/Synth.cpp

@@ -1,17 +1,20 @@
 #include "Synth.h"
+#include "FilterFactory.h"
 #include "KeyBoard.h"
 #include "Logger.h"
 #include "OscillatorType.h"
 #include "Settings.h"
-#include "FilterFactory.h"
-#include "LFO.h"
+#include "LowPassStateVariableFilter.h"
 
 Synth::Synth(/* args */) {
     m_lfo = new LFO();
+    m_lfo->SetFreq(5.0);
     AddOscillator();
     AddOscillator();
     AddEffect(new ADSR());
-    AddEffect(FilterFactory::GetDefaultFilter());
+    // todo: implement state-variable filters in a factory
+    AddEffect((StateVariableFilter*)new LowPassStateVariableFilter());
+    // AddEffect(FilterFactory::GetDefaultFilter());
     for (size_t i = 0; i < STREAM_BUFFER_SIZE; i++) {
         float sample = 0.0f;
         m_out_signal.push_back(sample);
@@ -38,8 +41,15 @@ void Synth::GetNote() {
 }
 
 void Synth::ApplyEffects() {
-    for (IEffect* effect : m_effects) {
-        effect->Process(m_out_signal);
+    auto* adsr = m_effects[0];
+    adsr->Process(m_out_signal);
+
+    StateVariableFilter* filter = (StateVariableFilter*)m_effects[1];
+    // assert(filter);
+
+    for (std::size_t i = 0; i < m_out_signal.size(); i++) {
+        ApplyFilterLfo();
+        m_out_signal[i] = filter->Process(m_out_signal[i]);
     }
 }
 
@@ -56,8 +66,7 @@ void Synth::UntriggerNoteOnEffects() {
 }
 
 void Synth::AddOscillator() {
-    m_oscillators.push_back(
-        new Oscillator(OscillatorType::Sine, 0.0f, VOLUME));
+    m_oscillators.push_back(new Oscillator(OscillatorType::Sine, 0.0f, VOLUME));
 }
 
 void Synth::Trigger(Note input) {
@@ -73,15 +82,16 @@ void Synth::Trigger(Note input) {
 // todo: fix this
 void Synth::ApplyFilterLfo() {
     float dt = m_lfo->Process();
-    Filter* filter = (Filter*)m_effects[1];
+    StateVariableFilter* filter = (StateVariableFilter*)m_effects[1];
     float freq = filter->GetFreq();
-    //todo: check formula
-    //filter->SetParameters(freq + dt * 0.2f, filter->GetRes(), filter->GetPeakGain());
+    // todo: check formula
+    // write_log("LFO DT: %f\n", dt);
+    filter->SetParameters(freq + dt, filter->GetRes(), filter->GetPeakGain());
 }
 
 void Synth::Process() {
-    //todo: on each sample. 
-    //in order to do that, we need to move to per-sample processing
+    // todo: on each sample.
+    // in order to do that, we need to move to per-sample processing
     //ApplyFilterLfo();
     GetNote();
     ApplyEffects();
@@ -96,9 +106,10 @@ void Synth::Release() {
 void Synth::AddEffect(IEffect* fx) { m_effects.push_back(fx); }
 
 void Synth::SetFilter(FilterType type) {
-    Filter* old_filter = this->GetFilter();
+    StateVariableFilter* old_filter = this->GetFilter();
     if (!old_filter->IsSameFilterType(type)) {
-        Filter* new_filter = FilterFactory::CreateFilter(old_filter, type);
+        // todo: implement other types of state variable filters;
+        StateVariableFilter* new_filter = (StateVariableFilter*)new LowPassStateVariableFilter(old_filter); // FilterFactory::CreateFilter(old_filter, type);
         delete old_filter;
         m_effects[1] = new_filter;
     }