add setting to disable DC offset correction

src/engine/blip_buf.c

@@ -67,6 +67,7 @@ struct blip_t
 	int avail;
 	int size;
 	int integrator;
+        unsigned char hipass;
 };
 
 typedef int buf_t;
@@ -119,6 +120,7 @@ blip_t* blip_new( int size )
 	{
 		m->factor = time_unit / blip_max_ratio;
 		m->size   = size;
+                m->hipass = 1;
 		blip_clear( m );
 		check_assumptions();
 	}
@@ -135,6 +137,10 @@ void blip_delete( blip_t* m )
 	}
 }
 
+void blip_set_dc( blip_t* m, unsigned char enable ) {
+  m->hipass=enable;
+}
+
 void blip_set_rates( blip_t* m, double clock_rate, double sample_rate )
 {
 	double factor = time_unit * sample_rate / clock_rate;
@@ -231,7 +237,9 @@ int blip_read_samples( blip_t* m, short out [], int count, int stereo )
 			out += step;
 			
 			/* High-pass filter */
-			sum -= s << (delta_bits - bass_shift);
+                        if (m->hipass) {
+			  sum -= s << (delta_bits - bass_shift);
+                        }
 		}
 		while ( in != end );
 		m->integrator = sum;

src/engine/blip_buf.h

@@ -5,6 +5,9 @@ Sample buffer that resamples from input clock rate to output sample rate */
 #ifndef BLIP_BUF_H 
 #define BLIP_BUF_H
 
+// MODIFIED by tildearrow:
+// - add option to disable high-pass filter
+
 #ifdef __cplusplus
 	extern "C" {
 #endif
@@ -18,6 +21,9 @@ so that there are blip_max_ratio clocks per sample. Returns pointer to new
 buffer, or NULL if insufficient memory. */
 blip_t* blip_new( int sample_count );
 
+/** (tildearrow) sets whether to enable high-pass filter. */
+void blip_set_dc( blip_t*, unsigned char enable );
+
 /** Sets approximate input clock rate and output sample rate. For every
 clock_rate input clocks, approximately sample_rate samples are generated. */
 void blip_set_rates( blip_t*, double clock_rate, double sample_rate );

src/engine/blip_buf.txt

@@ -4,6 +4,11 @@ Author  : Shay Green <gblargg@gmail.com>
 Website : http://www.slack.net/~ant/
 License : GNU Lesser General Public License (LGPL)
 
+MODIFICATION DISCLAIMER
+-----------------------
+I have modified this library in order to add a function that disables the DC offset correction high-pass filter.
+  - tildearrow
+
 
 Contents
 --------

src/engine/dispatchContainer.cpp

@@ -96,8 +96,13 @@ void DivDispatchContainer::setRates(double gotRate) {
   rateMemory=gotRate;
 }
 
-void DivDispatchContainer::setQuality(bool lowQual) {
+void DivDispatchContainer::setQuality(bool lowQual, bool dcHiPass) {
   lowQuality=lowQual;
+  hiPass=dcHiPass;
+  for (int i=0; i<DIV_MAX_OUTPUTS; i++) {
+    if (bb[i]==NULL) continue;
+    blip_set_dc(bb[i],dcHiPass);
+  }
 }
 
 void DivDispatchContainer::grow(size_t size) {
@@ -123,6 +128,7 @@ void DivDispatchContainer::grow(size_t size) {
         logE("not enough memory!"); \
         return; \
       } \
+      blip_set_dc(bb[i],hiPass); \
       blip_set_rates(bb[i],dispatch->rate,rateMemory); \
  \
       if (bbIn[i]==NULL) bbIn[i]=new short[bbInLen]; \
@@ -621,6 +627,7 @@ void DivDispatchContainer::init(DivSystem sys, DivEngine* eng, int chanCount, do
     bbOut[i]=new short[bbInLen];
     memset(bbIn[i],0,bbInLen*sizeof(short));
     memset(bbOut[i],0,bbInLen*sizeof(short));
+    blip_set_dc(bb[i],hiPass);
   }
 }
 

src/engine/engine.cpp

@@ -3353,7 +3353,7 @@ bool DivEngine::switchMaster(bool full) {
   if (initAudioBackend()) {
     for (int i=0; i<song.systemLen; i++) {
       disCont[i].setRates(got.rate);
-      disCont[i].setQuality(lowQuality);
+      disCont[i].setQuality(lowQuality,dcHiPass);
     }
     if (!output->setRun(true)) {
       logE("error while activating audio!");
@@ -3452,10 +3452,14 @@ void DivEngine::initDispatch(bool isRender) {
   BUSY_BEGIN;
   logV("initializing dispatch...");
   if (isRender) logI("render cores set");
+
+  lowQuality=getConfInt("audioQuality",0);
+  dcHiPass=getConfInt("audioHiPass",1);
+
   for (int i=0; i<song.systemLen; i++) {
     disCont[i].init(song.system[i],this,getChannelCount(song.system[i]),got.rate,song.systemFlags[i],isRender);
     disCont[i].setRates(got.rate);
-    disCont[i].setQuality(lowQuality);
+    disCont[i].setQuality(lowQuality,dcHiPass);
   }
   if (song.patchbayAuto) {
     saveLock.lock();
@@ -3534,7 +3538,6 @@ bool DivEngine::initAudioBackend() {
   }
 #endif
 
-  lowQuality=getConfInt("audioQuality",0);
   forceMono=getConfInt("forceMono",0);
   clampSamples=getConfInt("clampSamples",0);
   lowLatency=getConfInt("lowLatency",0);
@@ -3782,6 +3785,7 @@ bool DivEngine::init() {
     logE("not enough memory!");
     return false;
   }
+  blip_set_dc(samp_bb,0);
 
   samp_bbOut=new short[32768];
 

src/engine/engine.h

@@ -205,7 +205,7 @@ struct DivDispatchContainer {
   short* bbInMapped[DIV_MAX_OUTPUTS];
   short* bbIn[DIV_MAX_OUTPUTS];
   short* bbOut[DIV_MAX_OUTPUTS];
-  bool lowQuality, dcOffCompensation;
+  bool lowQuality, dcOffCompensation, hiPass;
   double rateMemory;
 
   // used in multi-thread
@@ -213,7 +213,7 @@ struct DivDispatchContainer {
   unsigned int size;
 
   void setRates(double gotRate);
-  void setQuality(bool lowQual);
+  void setQuality(bool lowQual, bool dcHiPass);
   void grow(size_t size);
   void acquire(size_t offset, size_t count);
   void flush(size_t count);
@@ -230,6 +230,7 @@ struct DivDispatchContainer {
     lastAvail(0),
     lowQuality(false),
     dcOffCompensation(false),
+    hiPass(true),
     rateMemory(0.0),
     cycles(0),
     size(0) {
@@ -389,6 +390,7 @@ class DivEngine {
   int chans;
   bool active;
   bool lowQuality;
+  bool dcHiPass;
   bool playing;
   bool freelance;
   bool shallStop, shallStopSched;
@@ -1224,6 +1226,7 @@ class DivEngine {
       chans(0),
       active(false),
       lowQuality(false),
+      dcHiPass(true),
       playing(false),
       freelance(false),
       shallStop(false),

src/engine/wavOps.cpp

@@ -111,7 +111,7 @@ void DivEngine::runExportThread() {
       if (initAudioBackend()) {
         for (int i=0; i<song.systemLen; i++) {
           disCont[i].setRates(got.rate);
-          disCont[i].setQuality(lowQuality);
+          disCont[i].setQuality(lowQuality,dcHiPass);
         }
         if (!output->setRun(true)) {
           logE("error while activating audio!");
@@ -223,7 +223,7 @@ void DivEngine::runExportThread() {
       if (initAudioBackend()) {
         for (int i=0; i<song.systemLen; i++) {
           disCont[i].setRates(got.rate);
-          disCont[i].setQuality(lowQuality);
+          disCont[i].setQuality(lowQuality,dcHiPass);
         }
         if (!output->setRun(true)) {
           logE("error while activating audio!");
@@ -349,7 +349,7 @@ void DivEngine::runExportThread() {
       if (initAudioBackend()) {
         for (int i=0; i<song.systemLen; i++) {
           disCont[i].setRates(got.rate);
-          disCont[i].setQuality(lowQuality);
+          disCont[i].setQuality(lowQuality,dcHiPass);
         }
         if (!output->setRun(true)) {
           logE("error while activating audio!");

src/gui/gui.h

@@ -1464,6 +1464,7 @@ class FurnaceGUI {
     int mainFontSize, patFontSize, headFontSize, iconSize;
     int audioEngine;
     int audioQuality;
+    int audioHiPass;
     int audioChans;
     int arcadeCore;
     int ym2612Core;
@@ -1656,6 +1657,7 @@ class FurnaceGUI {
       iconSize(16),
       audioEngine(DIV_AUDIO_SDL),
       audioQuality(0),
+      audioHiPass(1),
       audioChans(2),
       arcadeCore(0),
       ym2612Core(0),

src/gui/settings.cpp

@@ -1060,6 +1060,12 @@ void FurnaceGUI::drawSettings() {
           settingsChanged=true;
         }
 
+        bool audioHiPassB=settings.audioHiPass;
+        if (ImGui::Checkbox("DC offset correction",&audioHiPassB)) {
+          settings.audioHiPass=audioHiPassB;
+          settingsChanged=true;
+        }
+
         // SUBSECTION METRONOME
         CONFIG_SUBSECTION("Metronome");
         ImGui::AlignTextToFramePadding();
@@ -3574,6 +3580,7 @@ void FurnaceGUI::syncSettings() {
   settings.renderDriver=e->getConfString("renderDriver","");
   settings.sdlAudioDriver=e->getConfString("sdlAudioDriver","");
   settings.audioQuality=e->getConfInt("audioQuality",0);
+  settings.audioHiPass=e->getConfInt("audioHiPass",1);
   settings.audioBufSize=e->getConfInt("audioBufSize",1024);
   settings.audioRate=e->getConfInt("audioRate",44100);
   settings.arcadeCore=e->getConfInt("arcadeCore",0);
@@ -3756,6 +3763,7 @@ void FurnaceGUI::syncSettings() {
   clampSetting(settings.iconSize,2,48);
   clampSetting(settings.audioEngine,0,2);
   clampSetting(settings.audioQuality,0,1);
+  clampSetting(settings.audioHiPass,0,1);
   clampSetting(settings.audioBufSize,32,4096);
   clampSetting(settings.audioRate,8000,384000);
   clampSetting(settings.audioChans,1,16);
@@ -3987,7 +3995,9 @@ void FurnaceGUI::commitSettings() {
     settings.fdsCoreRender!=e->getConfInt("fdsCoreRender",0) ||
     settings.c64CoreRender!=e->getConfInt("c64CoreRender",0) ||
     settings.pokeyCoreRender!=e->getConfInt("pokeyCoreRender",1) ||
-    settings.opnCoreRender!=e->getConfInt("opnCoreRender",1)
+    settings.opnCoreRender!=e->getConfInt("opnCoreRender",1) ||
+    settings.audioQuality!=e->getConfInt("audioQuality",0) ||
+    settings.audioHiPass!=e->getConfInt("audioHiPass",1)
   );
 
   e->setConf("mainFontSize",settings.mainFontSize);
@@ -4001,6 +4011,7 @@ void FurnaceGUI::commitSettings() {
   e->setConf("renderDriver",settings.renderDriver);
   e->setConf("sdlAudioDriver",settings.sdlAudioDriver);
   e->setConf("audioQuality",settings.audioQuality);
+  e->setConf("audioHiPass",settings.audioHiPass);
   e->setConf("audioBufSize",settings.audioBufSize);
   e->setConf("audioRate",settings.audioRate);
   e->setConf("audioChans",settings.audioChans);