finally good audio

src/synth/Filter.hpp

@@ -33,7 +33,7 @@ private:
     void calculateCoefficients();
 
     Type type_ = Type::BiquadLowpass;
-    float sampleRate_ = 44100.0f;
+    float sampleRate_ = 1.0f;
 
     float frequency_ = 6000.0f;
     float q_ = 0.707f;

src/synth/Instruments/PianoString.cpp

@@ -12,7 +12,6 @@ PianoString::PianoString(ConfigService* config, LoggerService* logger) : Instrum
 
 void PianoString::noteOn(float frequency, float velocity) {
 
-    logger_->log("Piano", LogFlag::Debug, "Note On");
     active_ = true;
     frequency_ = frequency;
 
@@ -45,7 +44,6 @@ void PianoString::noteOn(float frequency, float velocity) {
 }
 
 void PianoString::noteOff() {
-    logger_->log("Piano", LogFlag::Debug, "Note Off");
     damping_ = 10.0f;
     recalculateConstants();
 }
@@ -67,41 +65,68 @@ bool PianoString::isActive() {
 
 float PianoString::process(bool& scopeTrigger) {
 
-    // simulate over string
+    // supersample
-    for(size_t i = 2; i < segmentCount_ - 2; i++) {
+    for(uint32_t n = 0; n < samplingSteps_; n++) {
-        float y_xx = stringY_current_[i-1] - 2.0f*stringY_current_[i] + stringY_current_[i+1];
-        float y_xxxx = stringY_current_[i-2] - 4.0f*stringY_current_[i-1] + 6.0f*stringY_current_[i] - 4.0f*stringY_current_[i+1] + stringY_current_[i+2];
-        stringY_next_[i] = a1_ * stringY_current_[i] + a2_ * stringY_previous_[i] + r2_ * y_xx - s2_ * y_xxxx;
-    }
-    stringY_next_[0] = 0.0f;
-    stringY_next_[1] = 0.0f;
-    stringY_next_[segmentCount_-1] = 0.0f;
-    stringY_next_[segmentCount_-2] = 0.0f;
 
-    stringY_previous_ = stringY_current_;
+        // simulate over string
-    stringY_current_ = stringY_next_;
+        for(size_t i = 2; i < segmentCount_ - 2; i++) {
+            float y_xx = stringY_current_[i-1] - 2.0f*stringY_current_[i] + stringY_current_[i+1];
+            float y_xxxx = stringY_current_[i-2] - 4.0f*stringY_current_[i-1] + 6.0f*stringY_current_[i] - 4.0f*stringY_current_[i+1] + stringY_current_[i+2];
+            stringY_next_[i] = a1_ * stringY_current_[i] + a2_ * stringY_previous_[i] + r2_ * y_xx - s2_ * y_xxxx;
+        }
+        stringY_next_[0] = 0.0f;
+        stringY_next_[1] = 0.0f;
+        stringY_next_[segmentCount_-1] = 0.0f;
+        stringY_next_[segmentCount_-2] = 0.0f;
+
+        stringY_previous_ = stringY_current_;
+        stringY_current_ = stringY_next_;
+    }
+
+    phaseTracker_ += frequency_ / sampleRate_;
+    if(phaseTracker_ > 1.0f) {
+        phaseTracker_ -= 1.0f;
+        scopeTrigger = true;
+    }
 
     float sampleOut = stringY_next_[static_cast<size_t>(samplePosition_*L_*segmentCount_)];
 
     rms_ = 0.99f * rms_ + 0.01f * sampleOut*sampleOut;
 
-    return 5.0f * sampleOut;
+    return sampleOut;
 
 }
 
 void PianoString::recalculateConstants() {
 
-    L_ = stringLength_ * std::pow(1.005f, -frequency_ + 20.0f) + 0.5f;
+    L_ = stringLength_ * std::pow(1.001f, -frequency_ + 20.0f) + 0.5f;
 
-    waveVelocity_ = 1.0f * frequency_ * L_;
+    waveVelocity_ = 2.0f * frequency_ * L_;
+
+    samplingSteps_ = 0;
+    do {
+        samplingSteps_++;
+        float effectiveSampleRate_ = sampleRate_ * static_cast<float>(samplingSteps_);
+        dt_ = 1.0f / effectiveSampleRate_;
+
+        float a = (waveVelocity_*dt_/L_)*(waveVelocity_*dt_/L_);
+        float b = 4.0f*(stiffness_*dt_/(L_*L_))*(stiffness_*dt_/(L_*L_));
+        if(stiffness_ < 0.00001f) { // avoid divide by zero
+            segmentCount_ = static_cast<size_t>((L_ * effectiveSampleRate_)/waveVelocity_) - 1;
+        } else {
+            segmentCount_ = static_cast<size_t>(std::sqrt((-a+std::sqrt(a*a+4.0*b))/(2.0*b))) - 1;
+        }
+
+    } while (segmentCount_ < 80);
+
+    segmentCount_ = std::min(segmentCount_, static_cast<size_t>(80));
 
     dx_ = L_ / static_cast<float>(segmentCount_);
-    dt_ = 1.0f / sampleRate_;
 
     r1_ = waveVelocity_ * dt_/dx_;
-    r2_ = std::pow(waveVelocity_ * dt_/dx_, 2.0f);
+    r2_ = (waveVelocity_ * dt_/dx_)*(waveVelocity_ * dt_/dx_);
-    s1_ = stiffness_ * dt_/std::pow(dx_, 2.0f);
+    s1_ = stiffness_ * dt_/(dx_*dx_);
-    s2_ = std::pow(stiffness_ * dt_/std::pow(dx_, 2.0f), 2.0f);
+    s2_ = (stiffness_ * dt_/(dx_*dx_))*(stiffness_ * dt_/(dx_*dx_));
     a1_ = 2.0f - 2.0f * damping_ * dt_;
     a2_ = 2.0f * damping_ * dt_ - 1.0f;
 }

src/synth/Instruments/PianoString.hpp

@@ -35,15 +35,15 @@ private:
     // constants
 
     // string parameters
-    size_t segmentCount_ = 50;
+    size_t segmentCount_ = 80;
     static constexpr float rho_ = 8000.0f; // density, steel, kg/m^3
     static constexpr float radius_ = 0.001f; // meters
     static constexpr float stringTension_ = 1200.0f; // string tension, N
-    static constexpr float stiffness_ = 0.000f; // stiffness coefficient
+    static constexpr float stiffness_ = 0.0f; // stiffness coefficient
     float damping_ = 0.5f; // damping coefficient
-    static constexpr float stringLength_ = 5.0f; // length of string at lowest frequency (20 hz)
+    static constexpr float stringLength_ = 4.0f; // length of string at lowest frequency (20 hz)
     static constexpr float strikePosition_ = 0.2f; // x of impulse location
-    static constexpr float impulseWidth_ = 0.02f; // x of impulse width
+    static constexpr float impulseWidth_ = 0.1f; // x of impulse width
     static constexpr float impulseVelocity_ = 10000.0f; // x/t of impulse magnitude
     static constexpr float samplePosition_ = 0.1f; // percentage along L of sampling for audio
     float crossSectionalArea_ = pi * std::pow(radius_, 2.0f); // string cross sectional area, assuming circular
@@ -54,6 +54,9 @@ private:
     // f0_ = waveVelocity_ / (2.0f * stringLength_); // fundamental frequency of a non-stiff string
     // f1_ = f0_ * std::sqrt(1.0f + stiffness_); // fundamental frequency of the stiff string
 
+    uint32_t samplingSteps_ = 1;
+    float phaseTracker_ = 0.0f;
+
     float dx_ = L_ / static_cast<float>(segmentCount_);
     float dt_ = 1.0f / sampleRate_;
 

src/synth/Synth.cpp

@@ -63,7 +63,7 @@ void Synth::process(float* out, size_t nFrames) {
             mix += voices_[j].process(temp);
             if(j == lowestVoice) triggered = temp;
         }
-        mix = tanh(mix/4.0f); // prevent clipping
+        mix = tanh(mix); // prevent clipping
 
         sampleOut = filter_.biquadProcess(mix);
         out[2*i] = sampleOut;