From 0c0cbd01d8f97e0af6a72f41a41690d38ccc6a01 Mon Sep 17 00:00:00 2001
From: Leandro Nini <drfiemost@users.sourceforge.net>
Date: Sun, 28 Jun 2026 09:02:37 +0200
Subject: [PATCH 1/2] Make the 6581 waveform offset adjustable (#13)

---
 src/SID.cpp             | 12 +++++++++---
 src/SID.h               |  7 +++++++
 src/State.cpp           |  2 ++
 src/State.h             |  1 +
 src/residfp/residfp.cpp |  5 +++++
 src/residfp/residfp.h   |  9 +++++++++
 6 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/src/SID.cpp b/src/SID.cpp
index 04ec837..8f985f1 100644
--- a/src/SID.cpp
+++ b/src/SID.cpp
@@ -142,6 +142,7 @@ SID::SID() :
     filter6581(new Filter6581()),
     filter8580(new Filter8580()),
     resampler(nullptr),
+    offset_6581(OFFSET_6581),
     cws(AVERAGE),
     dacLeakage(1.0),
     p(new Params)
@@ -269,8 +270,7 @@ void SID::setChipModel(ChipModel new_model)
         Dac dacBuilder(OSC_DAC_BITS);
         dacBuilder.kinkedDac(model, dacLeakage);
 
-        //const double offset = dacBuilder.getOutput(is6581 ? OFFSET_6581 : OFFSET_8580);
-        const double offset = dacBuilder.getOutput(is6581 ? OFFSET_6581 : 0x7ff, is6581);
+        const double offset = dacBuilder.getOutput(is6581 ? offset_6581 : 0x800, is6581);
 
         for (unsigned int i = 0; i < (1 << OSC_DAC_BITS); i++)
         {
@@ -616,7 +616,6 @@ void SID::setPaddle(uint8_t x, uint8_t y)
     paddleY = y;
 }
 
-
 void SID::setDacLeakage(double level)
 {
 #ifdef HAVE_CXX17
@@ -627,4 +626,11 @@ void SID::setDacLeakage(double level)
     setChipModel(model);
 }
 
+void SID::setOffset6581(double offset)
+{
+    // TODO determine a reasonable range
+    offset_6581 = 0x380 + static_cast<unsigned int>(offset * 0x20);
+    setChipModel(model);
+}
+
 } // namespace reSIDfp
diff --git a/src/SID.h b/src/SID.h
index b939405..39cf53c 100644
--- a/src/SID.h
+++ b/src/SID.h
@@ -98,6 +98,8 @@ class SID
     /// Time until #voiceSync must be run.
     unsigned int nextVoiceSync;
 
+    unsigned int offset_6581;
+
     /// Currently active chip model.
     ChipModel model;
 
@@ -366,6 +368,11 @@ class SID
      * Set the DAC leakage level.
      */
     void setDacLeakage(double level);
+
+    /*
+     * Set the 6581 wave offset.
+     */
+    void setOffset6581(double offset);
 };
 
 } // namespace reSIDfp
diff --git a/src/State.cpp b/src/State.cpp
index 27c843e..714dda6 100644
--- a/src/State.cpp
+++ b/src/State.cpp
@@ -88,6 +88,7 @@ int State::saveState(SID &s, char* buffer, int size)
     state.bus_value = s.busValue;
     state.bus_value_ttl = s.busValueTtl;
     state.nextVoiceSync = s.nextVoiceSync;
+    state.offset_6581 = s.offset_6581;
     state.paddle_x = s.paddleX;
     state.paddle_y = s.paddleY;
     state.model = s.model;
@@ -199,6 +200,7 @@ void State::restoreState(SID &s, char* buffer, int size)
     s.busValue = state.bus_value;
     s.busValueTtl = state.bus_value_ttl;
     s.nextVoiceSync = state.nextVoiceSync;
+    s.offset_6581 = state.offset_6581;
     s.paddleX = state.paddle_x;
     s.paddleY = state.paddle_y;
     s.model = state.model;
diff --git a/src/State.h b/src/State.h
index 4593fe4..8089f32 100644
--- a/src/State.h
+++ b/src/State.h
@@ -63,6 +63,7 @@ struct State
     // SID
     int bus_value_ttl;
     unsigned int nextVoiceSync;
+    unsigned int offset_6581;
     ChipModel model;
     CombinedWaveforms cws;
     double dacLeakage;
diff --git a/src/residfp/residfp.cpp b/src/residfp/residfp.cpp
index e82449c..fc1c767 100644
--- a/src/residfp/residfp.cpp
+++ b/src/residfp/residfp.cpp
@@ -155,6 +155,11 @@ void residfp::enableOld6581caps(bool enable)
     sid.enableOld6581caps(enable);
 }
 
+void residfp::setOffset6581(double offset)
+{
+    sid.setOffset6581(offset);
+}
+
 void residfp::setPaddle(unsigned char x, unsigned char y)
 {
     sid.setPaddle(x, y);
diff --git a/src/residfp/residfp.h b/src/residfp/residfp.h
index 2bb23ce..ed281fd 100644
--- a/src/residfp/residfp.h
+++ b/src/residfp/residfp.h
@@ -290,6 +290,15 @@ class RESIDFP_EXTERN residfp
      * @since 1.2
      */
     void setDacLeakage(double level);
+
+    /**
+     * Set the 6581 wave offset.
+     *
+     * @param offset the waveform offset, between 0 and 1
+     *
+     * @since 1.2
+     */
+    void setOffset6581(double offset);
 };
 
 }

From e7037e38d268fb3f66c0e43d5a428356e457fd34 Mon Sep 17 00:00:00 2001
From: Leandro Nini <drfiemost@users.sourceforge.net>
Date: Sun, 28 Jun 2026 14:17:37 +0200
Subject: [PATCH 2/2] Update

---
 src/SID.cpp           | 2 +-
 src/residfp/residfp.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/SID.cpp b/src/SID.cpp
index 8f985f1..8fe4c5f 100644
--- a/src/SID.cpp
+++ b/src/SID.cpp
@@ -629,7 +629,7 @@ void SID::setDacLeakage(double level)
 void SID::setOffset6581(double offset)
 {
     // TODO determine a reasonable range
-    offset_6581 = 0x380 + static_cast<unsigned int>(offset * 0x20);
+    offset_6581 = 0x380 + static_cast<unsigned int>((1. - offset) * 0x200);
     setChipModel(model);
 }
 
diff --git a/src/residfp/residfp.h b/src/residfp/residfp.h
index ed281fd..8ff4a48 100644
--- a/src/residfp/residfp.h
+++ b/src/residfp/residfp.h
@@ -293,8 +293,9 @@ class RESIDFP_EXTERN residfp
 
     /**
      * Set the 6581 wave offset.
+     * Affects the volume of digi samples.
      *
-     * @param offset the waveform offset, between 0 and 1
+     * @param offset the waveform offset, between 0 (faint digis) and 1 (loud digis)
      *
      * @since 1.2
      */