From bdaa77dcf038db13944420d41000db497e7b4297 Mon Sep 17 00:00:00 2001
From: yaw-man <ywmn@proton.me>
Date: Fri, 19 Aug 2022 16:18:51 -0300
Subject: [PATCH] Tweak yaw-shepard

---
 src/yaw-shepard/synth.cpp | 12 +++++++-----
 src/yaw-shepard/synth.h   |  6 +++---
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/src/yaw-shepard/synth.cpp b/src/yaw-shepard/synth.cpp
index 097ed5a..cbb5f5e 100644
--- a/src/yaw-shepard/synth.cpp
+++ b/src/yaw-shepard/synth.cpp
@@ -12,7 +12,7 @@ static constexpr double getAmplitude( double hz )
 {
   if( hz < 20.0 )       return 0.0;
   if( hz < 440.0 )      return hz / 440.0;
-  if( hz < 16000.0 )    return (16000.0 - hz) / 15560.0;
+  if( hz < 10000.0 )    return (10000.0 - hz) / 9560.0;
   return 0.0;
 }
 
@@ -42,14 +42,14 @@ void Synth::process(float* output, const uint32_t frames)
 
             //Don't bother rendering anything over the Nyquist rate.
             if( hz > hzNyq ) break;
-            output[i] += getAmplitude(hz) * sin(2.0 * M_PI * phase);
+            output[i] += getAmplitude(hz) * (phase > 0.5); // * sin(2.0 * M_PI * phase);
 
             //Remember phase, move to higher overtone.
             phases[(voice + idxFund) & VOICE_MASK] = phase;
             hz *= ratio;
         }
 
-        output[i] *= volume;
+        output[i] *= volume / static_cast<double>(NUM_VOICES);
     }
 
     //Make timbre cyclical.
@@ -81,7 +81,7 @@ void Synth::process(float* output, const uint32_t frames)
 void Synth::setSampleRate(double oldRate, double newRate){
     sampleInterval = 1.0 / newRate;
     hzNyq = newRate / 2;
-    ratioSlewRate *= newRate / oldRate;
+    ratioSlewRate = pow(ratioSlewRate, oldRate / newRate);
     hzShift = pow(hzShift, newRate / oldRate);
 }
 
@@ -92,11 +92,13 @@ void Synth::setFrequencyShift(double in){
     hzShift = exp2(2.0 * (in - 0.5) * sampleInterval);
 }
 
+static constexpr double minRatio = 1.0;
+static constexpr double maxRatio = 3.0;
 //Slew to given ratio.
 //0 : next voice is one fifth  above previous voice.
 //1 : next voice is one octave above previous voice.
 void Synth::setTargetRatio(double in){
-    targetRatio = 1.5 + in * 0.5;
+    targetRatio = minRatio + in * (maxRatio - minRatio);
 }
 
 void Synth::setVolume(double in){
diff --git a/src/yaw-shepard/synth.h b/src/yaw-shepard/synth.h
index f4a15c5..15da8c3 100644
--- a/src/yaw-shepard/synth.h
+++ b/src/yaw-shepard/synth.h
@@ -7,8 +7,8 @@ struct Voice
     double phase;
 };
 
-constexpr int NUM_VOICES = 256;
-constexpr uchar VOICE_MASK = 0xFF;
+constexpr unsigned int NUM_VOICES = 64;
+constexpr unsigned int VOICE_MASK = NUM_VOICES - 1;
 
 class Synth
 {
@@ -25,7 +25,7 @@ private:
     //Phase of each voice, considered as a period function on the unit interval.
     std::array<double, NUM_VOICES> phases = {0};
     //Index of lowest voice in phase array.
-    uchar idxFund = 0;
+    unsigned int idxFund = 0;
     float volume = 0.0f;
     double hzFund = 32.7;
     double hzShift = 1.0;