patch Synth_Dexed PluginFX to use zero cross detection

.github/workflows/build.yml

@@ -39,6 +39,11 @@ jobs:
           wget -q https://developer.arm.com/-/media/Files/downloads/gnu-a/10.3-2021.07/binrel/gcc-arm-10.3-2021.07-x86_64-aarch64-none-elf.tar.xz
           tar xf gcc-arm-10.3-2021.07-x86_64-aarch64-none-elf.tar.xz
 
+      # Patch Synth_Dexed PluginFX
+      - name: Patch Synth_Dexed
+        run: |
+          ( cd Synth_Dexed ; patch -p1 < ../src/patches/0001-PluginFX-change-gain-at-zero-crossing.patch )
+
       - name: Build for Raspberry Pi 5 (64-bit)
         run: |
           set -ex
@@ -124,6 +129,11 @@ jobs:
           wget -q https://developer.arm.com/-/media/Files/downloads/gnu-a/10.3-2021.07/binrel/gcc-arm-10.3-2021.07-x86_64-arm-none-eabi.tar.xz
           tar xf gcc-arm-10.3-2021.07-x86_64-arm-none-eabi.tar.xz
 
+      # Patch Synth_Dexed PluginFX
+      - name: Patch Synth_Dexed
+        run: |
+          ( cd Synth_Dexed ; patch -p1 < ../src/patches/0001-PluginFX-change-gain-at-zero-crossing.patch )
+
       - name: Build for Raspberry Pi 2 (32-bit)
         run: |
           set -ex

src/patches/0001-PluginFX-change-gain-at-zero-crossing.patch

@@ -0,0 +1,73 @@
+From 7daa07bd662d1894bc312b81c6b9e79260e7a66a Mon Sep 17 00:00:00 2001
+From: Gergo Koteles <soyer@irl.hu>
+Date: Fri, 11 Jul 2025 20:28:52 +0200
+Subject: [PATCH] PluginFX change gain at zero crossing
+
+---
+ src/PluginFx.cpp | 26 +++++++++++++++++++-------
+ src/PluginFx.h   |  2 ++
+ 2 files changed, 21 insertions(+), 7 deletions(-)
+
+diff --git a/src/PluginFx.cpp b/src/PluginFx.cpp
+index 7c3a1ab..2b7bb9b 100644
+--- a/src/PluginFx.cpp
++++ b/src/PluginFx.cpp
+@@ -56,6 +56,7 @@ PluginFx::PluginFx() {
+   Cutoff = 1.0;
+   Reso = 0.0;
+   Gain = 1.0;
++  aGain = 1.0;
+ }
+ 
+ void PluginFx::init(FRAC_NUM sr) {
+@@ -117,16 +118,27 @@ void PluginFx::process(float *work, uint16_t sampleSize) {
+ 
+   dc_od = work[sampleSize - 1];
+ 
+-  // Gain
+-  if (Gain == 0.0)
+-  {
++  if (Gain != aGain) {
+     for (uint16_t i = 0; i < sampleSize; i++ )
+-      work[i] = 0.0;
++    {
++      if (i != 0 && work[i] >= 0 && work[i-1] <= 0)
++        aGain = Gain;
++      work[i] *= aGain;
++    }
+   }
+-  else if ( Gain != 1.0)
++  else
+   {
+-    for (uint16_t i = 0; i < sampleSize; i++ )
+-      work[i] *= Gain;
++    // Gain
++    if (aGain == 0.0)
++    {
++      for (uint16_t i = 0; i < sampleSize; i++ )
++        work[i] = 0.0;
++    }
++    else if ( aGain != 1.0)
++    {
++      for (uint16_t i = 0; i < sampleSize; i++ )
++        work[i] *= aGain;
++    }
+   }
+ 
+   // don't apply the LPF if the cutoff is to maximum
+diff --git a/src/PluginFx.h b/src/PluginFx.h
+index 090e241..c27ccc5 100644
+--- a/src/PluginFx.h
++++ b/src/PluginFx.h
+@@ -67,6 +67,8 @@ class PluginFx {
+     float Reso;
+     float Gain;
+ 
++    float aGain;
++
+     void init(FRAC_NUM sampleRate);
+     void process(float *work, uint16_t sampleSize);
+     float getGain(void);
+-- 
+2.50.1
+