diff --git a/src/engine/dispatch.h b/src/engine/dispatch.h
index 0ec3a295b..c6486f26b 100644
--- a/src/engine/dispatch.h
+++ b/src/engine/dispatch.h
@@ -384,7 +384,8 @@ class DivDispatch {
      virtual ~DivDispatch();
 };
 
-#define NOTE_PERIODIC(x) parent->calcBaseFreq(chipClock,CHIP_DIVIDER,x,true)
+#define NOTE_PERIODIC(x) round(parent->calcBaseFreq(chipClock,CHIP_DIVIDER,x,true))
+#define NOTE_PERIODIC_NOROUND(x) parent->calcBaseFreq(chipClock,CHIP_DIVIDER,x,true)
 #define NOTE_FREQUENCY(x) parent->calcBaseFreq(chipClock,CHIP_FREQBASE,x,false)
 
 #define COLOR_NTSC (315000000.0/88.0)
diff --git a/src/engine/engine.cpp b/src/engine/engine.cpp
index e0c149752..48f88bfa1 100644
--- a/src/engine/engine.cpp
+++ b/src/engine/engine.cpp
@@ -815,11 +815,19 @@ void DivEngine::playSub(bool preserveDrift, int goalRow) {
   cmdStream.clear();
 }
 
+/*
 int DivEngine::calcBaseFreq(double clock, double divider, int note, bool period) {
   double base=(period?(song.tuning*0.0625):song.tuning)*pow(2.0,(float)(note+3)/12.0);
   return period?
          round((clock/base)/divider):
          base*(divider/clock);
+}*/
+
+double DivEngine::calcBaseFreq(double clock, double divider, int note, bool period) {
+  double base=(period?(song.tuning*0.0625):song.tuning)*pow(2.0,(float)(note+3)/12.0);
+  return period?
+         (clock/base)/divider:
+         base*(divider/clock);
 }
 
 int DivEngine::calcFreq(int base, int pitch, bool period, int octave) {
diff --git a/src/engine/engine.h b/src/engine/engine.h
index 1aa2b0c53..1eca56123 100644
--- a/src/engine/engine.h
+++ b/src/engine/engine.h
@@ -326,7 +326,7 @@ class DivEngine {
     void setConf(String key, String value);
 
     // calculate base frequency/period
-    int calcBaseFreq(double clock, double divider, int note, bool period);
+    double calcBaseFreq(double clock, double divider, int note, bool period);
 
     // calculate frequency/period
     int calcFreq(int base, int pitch, bool period=false, int octave=0);
diff --git a/src/engine/platform/amiga.cpp b/src/engine/platform/amiga.cpp
index d160d1125..13cb9604c 100644
--- a/src/engine/platform/amiga.cpp
+++ b/src/engine/platform/amiga.cpp
@@ -131,15 +131,15 @@ void DivPlatformAmiga::tick() {
     if (chan[i].std.hadArp) {
       if (!chan[i].inPorta) {
         if (chan[i].std.arpMode) {
-          chan[i].baseFreq=off*NOTE_PERIODIC(chan[i].std.arp);
+          chan[i].baseFreq=round(off*NOTE_PERIODIC_NOROUND(chan[i].std.arp));
         } else {
-          chan[i].baseFreq=off*NOTE_PERIODIC(chan[i].note+chan[i].std.arp);
+          chan[i].baseFreq=round(off*NOTE_PERIODIC_NOROUND(chan[i].note+chan[i].std.arp));
         }
       }
       chan[i].freqChanged=true;
     } else {
       if (chan[i].std.arpMode && chan[i].std.finishedArp) {
-        chan[i].baseFreq=off*NOTE_PERIODIC(chan[i].note);
+        chan[i].baseFreq=round(off*NOTE_PERIODIC_NOROUND(chan[i].note));
         chan[i].freqChanged=true;
       }
     }
@@ -183,7 +183,7 @@ int DivPlatformAmiga::dispatch(DivCommand c) {
         }
       }
       if (c.value!=DIV_NOTE_NULL) {
-        chan[c.chan].baseFreq=off*NOTE_PERIODIC(c.value);
+        chan[c.chan].baseFreq=round(off*NOTE_PERIODIC_NOROUND(c.value));
       }
       if (chan[c.chan].sample<0 || chan[c.chan].sample>=parent->song.sampleLen) {
         chan[c.chan].sample=-1;
@@ -241,7 +241,18 @@ int DivPlatformAmiga::dispatch(DivCommand c) {
       chan[c.chan].keyOn=true;
       break;
     case DIV_CMD_NOTE_PORTA: {
-      int destFreq=NOTE_PERIODIC(c.value2);
+      DivInstrument* ins=parent->getIns(chan[c.chan].ins);
+      chan[c.chan].sample=ins->amiga.initSample;
+      double off=1.0;
+      if (chan[c.chan].sample>=0 && chan[c.chan].sample<parent->song.sampleLen) {
+        DivSample* s=parent->getSample(chan[c.chan].sample);
+        if (s->centerRate<1) {
+          off=1.0;
+        } else {
+          off=8363.0/(double)s->centerRate;
+        }
+      }
+      int destFreq=round(off*NOTE_PERIODIC_NOROUND(c.value2));
       bool return2=false;
       if (destFreq>chan[c.chan].baseFreq) {
         chan[c.chan].baseFreq+=c.value;
@@ -273,7 +284,7 @@ int DivPlatformAmiga::dispatch(DivCommand c) {
           off=8363.0/(double)s->centerRate;
         }
       }
-      chan[c.chan].baseFreq=off*NOTE_PERIODIC(c.value+((chan[c.chan].std.willArp && !chan[c.chan].std.arpMode)?(chan[c.chan].std.arp-12):(0)));
+      chan[c.chan].baseFreq=round(off*NOTE_PERIODIC_NOROUND(c.value+((chan[c.chan].std.willArp && !chan[c.chan].std.arpMode)?(chan[c.chan].std.arp-12):(0))));
       chan[c.chan].freqChanged=true;
       chan[c.chan].note=c.value;
       break;
diff --git a/src/engine/platform/segapcm.cpp b/src/engine/platform/segapcm.cpp
index c0366a18a..361cef63c 100644
--- a/src/engine/platform/segapcm.cpp
+++ b/src/engine/platform/segapcm.cpp
@@ -87,15 +87,15 @@ void DivPlatformSegaPCM::tick() {
     if (chan[i].std.hadArp) {
       if (!chan[i].inPorta) {
         if (chan[i].std.arpMode) {
-          chan[i].baseFreq=(chan[i].std.arp<<6)+baseFreqOff;
+          chan[i].baseFreq=(chan[i].std.arp<<6);
         } else {
-          chan[i].baseFreq=((chan[i].note+(signed char)chan[i].std.arp)<<6)+baseFreqOff;
+          chan[i].baseFreq=((chan[i].note+(signed char)chan[i].std.arp)<<6);
         }
       }
       chan[i].freqChanged=true;
     } else {
       if (chan[i].std.arpMode && chan[i].std.finishedArp) {
-        chan[i].baseFreq=(chan[i].note<<6)+baseFreqOff;
+        chan[i].baseFreq=(chan[i].note<<6);
         chan[i].freqChanged=true;
       }
     }
@@ -113,7 +113,7 @@ void DivPlatformSegaPCM::tick() {
           DivSample* s=parent->getSample(chan[i].pcm.sample);
           off=(double)s->centerRate/8363.0;
         }
-        chan[i].pcm.freq=MIN(255,((off*parent->song.tuning*pow(2.0,double(chan[i].freq+256)/(64.0*12.0)))*255)/31250);
+        chan[i].pcm.freq=MIN(255,(15625+(off*parent->song.tuning*pow(2.0,double(chan[i].freq+256)/(64.0*12.0)))*255)/31250);
         if (dumpWrites && i>=8) {
           addWrite(0x10007+((i-8)<<3),chan[i].pcm.freq);
         }
@@ -250,17 +250,17 @@ int DivPlatformSegaPCM::dispatch(DivCommand c) {
       break;
     }
     case DIV_CMD_NOTE_PORTA: {
-      int destFreq=(c.value2<<6)+baseFreqOff;
+      int destFreq=(c.value2<<6);
       int newFreq;
       bool return2=false;
       if (destFreq>chan[c.chan].baseFreq) {
-        newFreq=chan[c.chan].baseFreq+c.value;
+        newFreq=chan[c.chan].baseFreq+c.value*4;
         if (newFreq>=destFreq) {
           newFreq=destFreq;
           return2=true;
         }
       } else {
-        newFreq=chan[c.chan].baseFreq-c.value;
+        newFreq=chan[c.chan].baseFreq-c.value*4;
         if (newFreq<=destFreq) {
           newFreq=destFreq;
           return2=true;
@@ -275,7 +275,7 @@ int DivPlatformSegaPCM::dispatch(DivCommand c) {
       break;
     }
     case DIV_CMD_LEGATO: {
-      chan[c.chan].baseFreq=(c.value<<6)+baseFreqOff;
+      chan[c.chan].baseFreq=(c.value<<6);
       chan[c.chan].freqChanged=true;
       break;
     }