From 18acf9eb95914fcfc686e4b0aab268bdfa5d9b60 Mon Sep 17 00:00:00 2001
From: yaw-man <ywmn@proton.me>
Date: Wed, 14 Sep 2022 19:05:04 -0400
Subject: [PATCH] Change timbre of shepard tone: overtones are now nearly
 harmonic

---
 src/yaw-shepard/synth.cpp | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/yaw-shepard/synth.cpp b/src/yaw-shepard/synth.cpp
index cbb5f5e..1dbeff3 100644
--- a/src/yaw-shepard/synth.cpp
+++ b/src/yaw-shepard/synth.cpp
@@ -40,13 +40,13 @@ void Synth::process(float* output, const uint32_t frames)
             phase += hz * sampleInterval;
             phase = frac(phase);
 
-            //Don't bother rendering anything over the Nyquist rate.
+            //Anti-aliasing: don't bother rendering anything over the Nyquist rate.
             if( hz > hzNyq ) break;
-            output[i] += getAmplitude(hz) * (phase > 0.5); // * sin(2.0 * M_PI * phase);
+            output[i] += getAmplitude(hz) * sin(2.0 * M_PI * phase);
 
             //Remember phase, move to higher overtone.
             phases[(voice + idxFund) & VOICE_MASK] = phase;
-            hz *= ratio;
+            hz *= ratio * (voice + 1.0) / (voice + 2.0);
         }
 
         output[i] *= volume / static_cast<double>(NUM_VOICES);
@@ -60,8 +60,8 @@ void Synth::process(float* output, const uint32_t frames)
             && getAmplitude(hzFund) < MIN_VOLUME)
         {
             ++idxFund;
-            hz *= ratio;
-            hzFund *= ratio;
+            hz *= 2.0 * ratio;
+            hzFund *= 2.0 * ratio;
         }
     }
 
@@ -72,8 +72,8 @@ void Synth::process(float* output, const uint32_t frames)
             && getAmplitude(hzFund) > MIN_VOLUME)
         {
             --idxFund;
-            hz /= ratio;
-            hzFund /= ratio;
+            hz /= 2.0 * ratio;
+            hzFund /= 2.0 * ratio;
         }
     }
 }
@@ -93,10 +93,10 @@ void Synth::setFrequencyShift(double in){
 }
 
 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.
+static constexpr double maxRatio = 1.05;
+//Slew to given inharmonicity ratio.
+//0 : next voice is exactly harmonic.
+//1 : next voice is 5% inharmonic.
 void Synth::setTargetRatio(double in){
     targetRatio = minRatio + in * (maxRatio - minRatio);
 }