diff --git a/src/engine/platform/opl.cpp b/src/engine/platform/opl.cpp
index 2c005ee9..d8426553 100644
--- a/src/engine/platform/opl.cpp
+++ b/src/engine/platform/opl.cpp
@@ -25,7 +25,7 @@
 #define rWrite(a,v) if (!skipRegisterWrites) {pendingWrites[a]=v;}
 #define immWrite(a,v) if (!skipRegisterWrites) {writes.emplace(a,v); if (dumpWrites) {addWrite(a,v);} }
 
-#define CHIP_FREQBASE 9440540
+#define CHIP_FREQBASE chipFreqBase
 
 // N = invalid
 #define N 255
@@ -456,9 +456,11 @@ int DivPlatformOPL::dispatch(DivCommand c) {
         chan[c.chan].outVol=chan[c.chan].vol;
       }
       if (chan[c.chan].insChanged) {
-        int ops=(slots[3][c.chan]!=255 && ins->fm.ops==4)?4:2;
+        int ops=(slots[3][c.chan]!=255 && ins->fm.ops==4 && oplType==3)?4:2;
         for (int i=0; i<ops; i++) {
-          unsigned short baseAddr=slotMap[slots[i][c.chan]];
+          unsigned char slot=slots[i][c.chan];
+          if (slot==255) continue;
+          unsigned short baseAddr=slotMap[slot];
           DivInstrumentFM::Operator& op=chan[c.chan].state.op[(ops==4)?orderedOpsL[i]:i];
 
           if (isMuted[c.chan]) {
@@ -812,12 +814,14 @@ void DivPlatformOPL::setOPLType(int type, bool drums) {
       slotsDrums=slotsOPL2Drums;
       slots=drums?slotsDrums:slotsNonDrums;
       chanMap=chanMapOPL2;
+      chipFreqBase=9440540*0.25;
       break;
     case 3:
       slotsNonDrums=slotsOPL3;
       slotsDrums=slotsOPL3Drums;
       slots=drums?slotsDrums:slotsNonDrums;
       chanMap=chanMapOPL3;
+      chipFreqBase=9440540;
       break;
   }
   oplType=type;
diff --git a/src/engine/platform/opl.h b/src/engine/platform/opl.h
index 32913a8d..7bd6118a 100644
--- a/src/engine/platform/opl.h
+++ b/src/engine/platform/opl.h
@@ -68,6 +68,7 @@ class DivPlatformOPL: public DivDispatch {
     const unsigned char** slotsDrums;
     const unsigned char** slots;
     const unsigned short* chanMap;
+    double chipFreqBase;
     int delay, oplType;
     unsigned char lastBusy;
 
diff --git a/src/engine/platform/sound/swan.cpp b/src/engine/platform/sound/swan.cpp
index 60052f61..685fefe9 100644
--- a/src/engine/platform/sound/swan.cpp
+++ b/src/engine/platform/sound/swan.cpp
@@ -85,7 +85,6 @@ void WSwan::SoundUpdate(uint32_t v30mz_timestamp)
   else if(ch == 2 && (control & 0x40) && sweep_value) // Sweep
   {
    uint32_t tmp_pt = 2048 - period[ch];
-   uint32_t meow_timestamp = v30mz_timestamp - run_time;
    uint32_t tmp_run_time = run_time;
 
    while(tmp_run_time)
@@ -107,7 +106,6 @@ void WSwan::SoundUpdate(uint32_t v30mz_timestamp)
      }
     }
 
-    meow_timestamp += sub_run_time;
     if(tmp_pt > 4)
     {
      period_counter[ch] -= sub_run_time;
@@ -116,7 +114,6 @@ void WSwan::SoundUpdate(uint32_t v30mz_timestamp)
       sample_pos[ch] = (sample_pos[ch] + 1) & 0x1F;
 
       MK_SAMPLE_CACHE;
-      SYNCSAMPLE(meow_timestamp + period_counter[ch]);
       period_counter[ch] += tmp_pt;
      }
     }
diff --git a/src/engine/platform/sound/swan.h b/src/engine/platform/sound/swan.h
index b1b0af74..a1d01fa5 100644
--- a/src/engine/platform/sound/swan.h
+++ b/src/engine/platform/sound/swan.h
@@ -76,7 +76,6 @@ private:
  uint32_t last_ts;
 
  uint8_t wsRAM[64];
- int16_t sBuf[2];
 };
 
 #endif
diff --git a/src/engine/platform/swan.cpp b/src/engine/platform/swan.cpp
index 8fdca1d4..21987180 100644
--- a/src/engine/platform/swan.cpp
+++ b/src/engine/platform/swan.cpp
@@ -152,7 +152,7 @@ void DivPlatformSwan::tick() {
   unsigned char sndCtrl=(pcm?0x20:0)|(sweep?0x40:0)|((noise>0)?0x80:0);
   for (int i=0; i<4; i++) {
     chan[i].std.next();
-    if (chan[i].std.willVol) {
+    if (chan[i].std.hadVol) {
       int env=chan[i].std.vol;
       if(parent->getIns(chan[i].ins)->type==DIV_INS_AMIGA) {
         env=MIN(env/4,15);
@@ -320,7 +320,7 @@ int DivPlatformSwan::dispatch(DivCommand c) {
     case DIV_CMD_VOLUME:
       if (chan[c.chan].vol!=c.value) {
         chan[c.chan].vol=c.value;
-        if (!chan[c.chan].std.willVol) {
+        if (!chan[c.chan].std.hadVol) {
           calcAndWriteOutVol(c.chan,15);
         }
       }
@@ -392,9 +392,7 @@ int DivPlatformSwan::dispatch(DivCommand c) {
       break;
     case DIV_CMD_PANNING: {
       chan[c.chan].pan=c.value;
-      if (!chan[c.chan].std.willVol) {
-        calcAndWriteOutVol(c.chan,15);
-      }
+      calcAndWriteOutVol(c.chan,chan[c.chan].std.willVol?chan[c.chan].std.vol:15);
       break;
     }
     case DIV_CMD_LEGATO:
diff --git a/src/gui/gui.cpp b/src/gui/gui.cpp
index 475d017c..dc72ccad 100644
--- a/src/gui/gui.cpp
+++ b/src/gui/gui.cpp
@@ -4969,6 +4969,7 @@ bool FurnaceGUI::loop() {
                 break;
               }
               case DIV_SYSTEM_GB:
+              case DIV_SYSTEM_SWAN:
               case DIV_SYSTEM_YM2610:
               case DIV_SYSTEM_YM2610_EXT:
               case DIV_SYSTEM_YM2610_FULL: