diff --git a/src/engine/engine.cpp b/src/engine/engine.cpp
index 81bf1aee7..5c552290a 100644
--- a/src/engine/engine.cpp
+++ b/src/engine/engine.cpp
@@ -2091,46 +2091,6 @@ const char** DivEngine::getRegisterSheet(int sys) {
   return disCont[sys].dispatch->getRegisterSheet();
 }
 
-void DivEngine::recalcChans() {
-  bool isInsTypePossible[DIV_INS_MAX];
-  chans=0;
-  int chanIndex=0;
-  memset(isInsTypePossible,0,DIV_INS_MAX*sizeof(bool));
-  for (int i=0; i<song.systemLen; i++) {
-    int chanCount=song.systemChans[i];
-    int firstChan=chans;
-    chans+=chanCount;
-    for (int j=0; j<chanCount; j++) {
-      sysOfChan[chanIndex]=song.system[i];
-      dispatchOfChan[chanIndex]=i;
-      dispatchChanOfChan[chanIndex]=j;
-      dispatchFirstChan[chanIndex]=firstChan;
-      chanIndex++;
-
-      if (sysDefs[song.system[i]]!=NULL) {
-        if (sysDefs[song.system[i]]->chanInsType[j][0]!=DIV_INS_NULL) {
-          isInsTypePossible[sysDefs[song.system[i]]->chanInsType[j][0]]=true;
-        }
-
-        if (sysDefs[song.system[i]]->chanInsType[j][1]!=DIV_INS_NULL) {
-          isInsTypePossible[sysDefs[song.system[i]]->chanInsType[j][1]]=true;
-        }
-      }
-    }
-  }
-
-  possibleInsTypes.clear();
-  for (int i=0; i<DIV_INS_MAX; i++) {
-    if (isInsTypePossible[i]) possibleInsTypes.push_back((DivInstrumentType)i);
-  }
-
-  checkAssetDir(song.insDir,song.ins.size());
-  checkAssetDir(song.waveDir,song.wave.size());
-  checkAssetDir(song.sampleDir,song.sample.size());
-
-  hasLoadedSomething=true;
-}
-
 void DivEngine::reset() {
   if (output) if (output->midiOut!=NULL) {
     output->midiOut->send(TAMidiMessage(TA_MIDI_MACHINE_STOP,0,0));
diff --git a/src/engine/engine.h b/src/engine/engine.h
index 1c7d989eb..6b5611eb0 100644
--- a/src/engine/engine.h
+++ b/src/engine/engine.h
@@ -463,7 +463,6 @@ class DivEngine {
   TAAudioDesc want, got;
   String exportPath;
   std::thread* exportThread;
-  int chans;
   bool configLoaded;
   bool active;
   bool lowQuality;
@@ -546,7 +545,6 @@ class DivEngine {
   std::vector<String> midiIns;
   std::vector<String> midiOuts;
   std::vector<DivCommand> cmdStream;
-  std::vector<DivInstrumentType> possibleInsTypes;
   std::vector<DivEffectContainer> effectInst;
   std::vector<int> curChanMask;
   static DivSysDef* sysDefs[DIV_MAX_CHIP_DEFS];
@@ -625,7 +623,6 @@ class DivEngine {
   bool perSystemEffect(int ch, unsigned char effect, unsigned char effectVal);
   bool perSystemPostEffect(int ch, unsigned char effect, unsigned char effectVal);
   bool perSystemPreEffect(int ch, unsigned char effect, unsigned char effectVal);
-  void recalcChans();
   void reset();
   void playSub(bool preserveDrift, int goalRow=0);
   void runMidiClock(int totalCycles=1);
@@ -716,10 +713,6 @@ class DivEngine {
     DivChannelData* curPat;
     DivSubSong* curSubSong;
     DivInstrument* tempIns;
-    DivSystem sysOfChan[DIV_MAX_CHANS];
-    int dispatchOfChan[DIV_MAX_CHANS];
-    int dispatchChanOfChan[DIV_MAX_CHANS];
-    int dispatchFirstChan[DIV_MAX_CHANS];
     bool keyHit[DIV_MAX_CHANS];
     float* oscBuf[DIV_MAX_OUTPUTS];
     float oscSize;
@@ -953,7 +946,7 @@ class DivEngine {
     const char* getSystemNameJ(DivSystem sys);
 
     // get sys definition
-    const DivSysDef* getSystemDef(DivSystem sys);
+    static const DivSysDef* getSystemDef(DivSystem sys);
 
     // get ROM export definition
     const DivROMExportDef* getROMExportDef(DivROMExportOptions opt);
@@ -1456,7 +1449,6 @@ class DivEngine {
     DivEngine():
       output(NULL),
       exportThread(NULL),
-      chans(0),
       configLoaded(false),
       active(false),
       lowQuality(false),
@@ -1591,10 +1583,6 @@ class DivEngine {
       mu5ROM(NULL) {
       memset(isMuted,0,DIV_MAX_CHANS*sizeof(bool));
       memset(keyHit,0,DIV_MAX_CHANS*sizeof(bool));
-      memset(dispatchFirstChan,0,DIV_MAX_CHANS*sizeof(int));
-      memset(dispatchChanOfChan,0,DIV_MAX_CHANS*sizeof(int));
-      memset(dispatchOfChan,0,DIV_MAX_CHANS*sizeof(int));
-      memset(sysOfChan,0,DIV_MAX_CHANS*sizeof(int));
       memset(vibTable,0,64*sizeof(short));
       memset(tremTable,0,128*sizeof(short));
       memset(effectSlotMap,-1,4096*sizeof(short));
diff --git a/src/engine/fileOps/dmf.cpp b/src/engine/fileOps/dmf.cpp
index dd4f93281..492f0c21f 100644
--- a/src/engine/fileOps/dmf.cpp
+++ b/src/engine/fileOps/dmf.cpp
@@ -1168,6 +1168,7 @@ bool DivEngine::loadDMF(unsigned char* file, size_t len) {
     }
 
     ds.systemName=getSongSystemLegacyName(ds,!getConfInt("noMultiSystem",0));
+    ds.recalcChans();
 
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
@@ -1175,7 +1176,6 @@ bool DivEngine::loadDMF(unsigned char* file, size_t len) {
     song.unload();
     song=ds;
     changeSong(0);
-    recalcChans();
     // always convert to normal sample mode (I have no idea how will I do export)
     convertLegacySampleMode();
     saveLock.unlock();
@@ -1289,7 +1289,7 @@ SafeWriter* DivEngine::saveDMF(unsigned char version) {
     lastError="maximum number of wavetables in .dmf is 64";
     return NULL;
   }
-  for (int i=0; i<chans; i++) {
+  for (int i=0; i<song.chans; i++) {
     for (int j=0; j<curSubSong->ordersLen; j++) {
       if (curOrders->ord[i][j]>0x7f) {
         logE("order %d, %d is out of range (0-127)!",i,j);
@@ -1356,7 +1356,7 @@ SafeWriter* DivEngine::saveDMF(unsigned char version) {
   w->writeI(curSubSong->patLen);
   w->writeC(curSubSong->ordersLen);
 
-  for (int i=0; i<chans; i++) {
+  for (int i=0; i<song.chans; i++) {
     for (int j=0; j<curSubSong->ordersLen; j++) {
       w->writeC(curOrders->ord[i][j]);
       if (version>=25) {
diff --git a/src/engine/fileOps/fc.cpp b/src/engine/fileOps/fc.cpp
index 6e4408a7d..8fbf49502 100644
--- a/src/engine/fileOps/fc.cpp
+++ b/src/engine/fileOps/fc.cpp
@@ -664,6 +664,8 @@ bool DivEngine::loadFC(unsigned char* file, size_t len) {
     ds.subsong[0]->optimizePatterns();
     ds.subsong[0]->rearrangePatterns();
 
+    ds.recalcChans();
+
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
     saveLock.lock();
diff --git a/src/engine/fileOps/ftm.cpp b/src/engine/fileOps/ftm.cpp
index 791269891..1fee6f053 100644
--- a/src/engine/fileOps/ftm.cpp
+++ b/src/engine/fileOps/ftm.cpp
@@ -2802,13 +2802,14 @@ bool DivEngine::loadFTM(unsigned char* file, size_t len, bool dnft, bool dnft_si
       }
     }
 
+    ds.recalcChans();
+
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
     saveLock.lock();
     song.unload();
     song=ds;
     changeSong(0);
-    recalcChans();
     saveLock.unlock();
     BUSY_END;
     if (active) {
diff --git a/src/engine/fileOps/fur.cpp b/src/engine/fileOps/fur.cpp
index a27bf30d7..7a22eed00 100644
--- a/src/engine/fileOps/fur.cpp
+++ b/src/engine/fileOps/fur.cpp
@@ -2129,6 +2129,7 @@ bool DivEngine::loadFur(unsigned char* file, size_t len, int variantID) {
     } else if (ds.version<237 && ds.linearPitch!=0) {
       addWarning("this song used partial pitch linearity, which has been removed from Furnace. you may have to adjust your song.");
     }
+    ds.recalcChans();
 
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
@@ -2136,7 +2137,6 @@ bool DivEngine::loadFur(unsigned char* file, size_t len, int variantID) {
     song.unload();
     song=ds;
     changeSong(0);
-    recalcChans();
     // removal of legacy sample mode
     if (song.version<239) {
       if (convertLegacySampleMode()) {
@@ -2242,7 +2242,7 @@ SafeWriter* DivEngine::saveFur(bool notPrimary) {
   // low short is pattern number
   std::vector<PatToWrite> patsToWrite;
   if (getConfInt("saveUnusedPatterns",0)==1) {
-    for (int i=0; i<chans; i++) {
+    for (int i=0; i<song.chans; i++) {
       for (size_t j=0; j<song.subsong.size(); j++) {
         DivSubSong* subs=song.subsong[j];
         for (int k=0; k<DIV_MAX_PATTERNS; k++) {
@@ -2253,7 +2253,7 @@ SafeWriter* DivEngine::saveFur(bool notPrimary) {
     }
   } else {
     bool alreadyAdded[DIV_MAX_PATTERNS];
-    for (int i=0; i<chans; i++) {
+    for (int i=0; i<song.chans; i++) {
       for (size_t j=0; j<song.subsong.size(); j++) {
         DivSubSong* subs=song.subsong[j];
         memset(alreadyAdded,0,DIV_MAX_PATTERNS*sizeof(bool));
@@ -2358,32 +2358,32 @@ SafeWriter* DivEngine::saveFur(bool notPrimary) {
     w->writeI(0);
   }
 
-  for (int i=0; i<chans; i++) {
+  for (int i=0; i<song.chans; i++) {
     for (int j=0; j<subSong->ordersLen; j++) {
       w->writeC(subSong->orders.ord[i][j]);
     }
   }
 
-  for (int i=0; i<chans; i++) {
+  for (int i=0; i<song.chans; i++) {
     w->writeC(subSong->pat[i].effectCols);
   }
 
-  for (int i=0; i<chans; i++) {
+  for (int i=0; i<song.chans; i++) {
     w->writeC(
       (subSong->chanShow[i]?1:0)|
       (subSong->chanShowChanOsc[i]?2:0)
     );
   }
 
-  for (int i=0; i<chans; i++) {
+  for (int i=0; i<song.chans; i++) {
     w->writeC(subSong->chanCollapse[i]);
   }
 
-  for (int i=0; i<chans; i++) {
+  for (int i=0; i<song.chans; i++) {
     w->writeString(subSong->chanName[i],false);
   }
 
-  for (int i=0; i<chans; i++) {
+  for (int i=0; i<song.chans; i++) {
     w->writeString(subSong->chanShortName[i],false);
   }
 
@@ -2518,32 +2518,32 @@ SafeWriter* DivEngine::saveFur(bool notPrimary) {
     w->writeString(subSong->name,false);
     w->writeString(subSong->notes,false);
 
-    for (int i=0; i<chans; i++) {
+    for (int i=0; i<song.chans; i++) {
       for (int j=0; j<subSong->ordersLen; j++) {
         w->writeC(subSong->orders.ord[i][j]);
       }
     }
 
-    for (int i=0; i<chans; i++) {
+    for (int i=0; i<song.chans; i++) {
       w->writeC(subSong->pat[i].effectCols);
     }
 
-    for (int i=0; i<chans; i++) {
+    for (int i=0; i<song.chans; i++) {
       w->writeC(
         (subSong->chanShow[i]?1:0)|
         (subSong->chanShowChanOsc[i]?2:0)
       );
     }
 
-    for (int i=0; i<chans; i++) {
+    for (int i=0; i<song.chans; i++) {
       w->writeC(subSong->chanCollapse[i]);
     }
 
-    for (int i=0; i<chans; i++) {
+    for (int i=0; i<song.chans; i++) {
       w->writeString(subSong->chanName[i],false);
     }
 
-    for (int i=0; i<chans; i++) {
+    for (int i=0; i<song.chans; i++) {
       w->writeString(subSong->chanShortName[i],false);
     }
 
diff --git a/src/engine/fileOps/it.cpp b/src/engine/fileOps/it.cpp
index 02d0b00a5..3fe6285a1 100644
--- a/src/engine/fileOps/it.cpp
+++ b/src/engine/fileOps/it.cpp
@@ -1675,7 +1675,8 @@ bool DivEngine::loadIT(unsigned char* file, size_t len) {
     ds.systemName="PC";
 
     // find subsongs
-    ds.findSubSongs(maxChan);    
+    ds.recalcChans();
+    ds.findSubSongs();
 
     // populate subsongs with default panning values
     for (size_t i=0; i<ds.subsong.size(); i++) {
@@ -1708,7 +1709,6 @@ bool DivEngine::loadIT(unsigned char* file, size_t len) {
     song.unload();
     song=ds;
     changeSong(0);
-    recalcChans();
     saveLock.unlock();
     BUSY_END;
     if (active) {
diff --git a/src/engine/fileOps/mod.cpp b/src/engine/fileOps/mod.cpp
index 5a8e3d3aa..7f933b27f 100644
--- a/src/engine/fileOps/mod.cpp
+++ b/src/engine/fileOps/mod.cpp
@@ -431,7 +431,8 @@ bool DivEngine::loadMod(unsigned char* file, size_t len) {
     ds.insLen=ds.ins.size();
 
     // find subsongs
-    ds.findSubSongs(chCount);
+    ds.recalcChans();
+    ds.findSubSongs();
     
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
@@ -439,7 +440,6 @@ bool DivEngine::loadMod(unsigned char* file, size_t len) {
     song.unload();
     song=ds;
     changeSong(0);
-    recalcChans();
     saveLock.unlock();
     BUSY_END;
     if (active) {
diff --git a/src/engine/fileOps/s3m.cpp b/src/engine/fileOps/s3m.cpp
index 1000273fb..b866b2920 100644
--- a/src/engine/fileOps/s3m.cpp
+++ b/src/engine/fileOps/s3m.cpp
@@ -1179,7 +1179,8 @@ bool DivEngine::loadS3M(unsigned char* file, size_t len) {
     }
 
     // find subsongs
-    ds.findSubSongs(DIV_MAX_CHANS);
+    ds.recalcChans();
+    ds.findSubSongs();
 
     // populate subsongs with default panning values
     if (masterVol&128) { // only in stereo mode
@@ -1215,7 +1216,6 @@ bool DivEngine::loadS3M(unsigned char* file, size_t len) {
     song.unload();
     song=ds;
     changeSong(0);
-    recalcChans();
     saveLock.unlock();
     BUSY_END;
     if (active) {
diff --git a/src/engine/fileOps/tfm.cpp b/src/engine/fileOps/tfm.cpp
index 015132de2..557ad351b 100644
--- a/src/engine/fileOps/tfm.cpp
+++ b/src/engine/fileOps/tfm.cpp
@@ -704,13 +704,14 @@ bool DivEngine::loadTFMv1(unsigned char* file, size_t len) {
     info.loopPos=loopPos;
     TFMParsePattern(info);
 
+    ds.recalcChans();
+
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
     saveLock.lock();
     song.unload();
     song=ds;
     changeSong(0);
-    recalcChans();
     saveLock.unlock();
     BUSY_END;
     if (active) {
@@ -904,13 +905,14 @@ bool DivEngine::loadTFMv2(unsigned char* file, size_t len) {
     info.loopPos=loopPos;
     TFMParsePattern(info);
 
+    ds.recalcChans();
+
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
     saveLock.lock();
     song.unload();
     song=ds;
     changeSong(0);
-    recalcChans();
     saveLock.unlock();
     BUSY_END;
     if (active) {
diff --git a/src/engine/fileOps/xm.cpp b/src/engine/fileOps/xm.cpp
index 3e0a0ef98..fe0ec35c1 100644
--- a/src/engine/fileOps/xm.cpp
+++ b/src/engine/fileOps/xm.cpp
@@ -1377,7 +1377,8 @@ bool DivEngine::loadXM(unsigned char* file, size_t len) {
     }
 
     // find subsongs
-    ds.findSubSongs(totalChans);
+    ds.recalcChans();
+    ds.findSubSongs();
 
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
@@ -1385,7 +1386,6 @@ bool DivEngine::loadXM(unsigned char* file, size_t len) {
     song.unload();
     song=ds;
     changeSong(0);
-    recalcChans();
     saveLock.unlock();
     BUSY_END;
     if (active) {
diff --git a/src/engine/song.cpp b/src/engine/song.cpp
index 798c5f1c4..7bf33dd9d 100644
--- a/src/engine/song.cpp
+++ b/src/engine/song.cpp
@@ -574,7 +574,7 @@ void DivSubSong::makePatUnique() {
   }
 }
 
-void DivSong::findSubSongs(int chans) {
+void DivSong::findSubSongs() {
   std::vector<DivSubSong*> newSubSongs;
   for (DivSubSong* i: subsong) {
     std::vector<int> subSongStart;
@@ -689,9 +689,50 @@ void DivSong::findSubSongs(int chans) {
   for (DivSubSong* i: newSubSongs) {
     subsong.push_back(i);
   }
-
 }
 
+void DivSong::recalcChans() {
+  bool isInsTypePossible[DIV_INS_MAX];
+  chans=0;
+  int chanIndex=0;
+  memset(isInsTypePossible,0,DIV_INS_MAX*sizeof(bool));
+  for (int i=0; i<systemLen; i++) {
+    int chanCount=systemChans[i];
+    int firstChan=chans;
+    chans+=chanCount;
+    for (int j=0; j<chanCount; j++) {
+      sysOfChan[chanIndex]=system[i];
+      dispatchOfChan[chanIndex]=i;
+      dispatchChanOfChan[chanIndex]=j;
+      dispatchFirstChan[chanIndex]=firstChan;
+      chanIndex++;
+
+      DivSysDef* sysDef=DivEngine::getSystemDef(system[i]);
+      if (sysDef!=NULL) {
+        if (sysDef->chanInsType[j][0]!=DIV_INS_NULL) {
+          isInsTypePossible[sysDef->chanInsType[j][0]]=true;
+        }
+
+        if (sysDef->chanInsType[j][1]!=DIV_INS_NULL) {
+          isInsTypePossible[sysDef->chanInsType[j][1]]=true;
+        }
+      }
+    }
+  }
+
+  possibleInsTypes.clear();
+  for (int i=0; i<DIV_INS_MAX; i++) {
+    if (isInsTypePossible[i]) possibleInsTypes.push_back((DivInstrumentType)i);
+  }
+
+  checkAssetDir(insDir,ins.size());
+  checkAssetDir(waveDir,wave.size());
+  checkAssetDir(sampleDir,sample.size());
+
+  hasLoadedSomething=true;
+}
+
+
 void DivSong::clearSongData() {
   for (DivSubSong* i: subsong) {
     i->clearData();
@@ -749,4 +790,4 @@ void DivSong::unload() {
     delete i;
   }
   subsong.clear();
-}
\ No newline at end of file
+}
diff --git a/src/engine/song.h b/src/engine/song.h
index fef22a7c4..83414452a 100644
--- a/src/engine/song.h
+++ b/src/engine/song.h
@@ -274,6 +274,7 @@ struct DivSong {
   bool isDMF;
 
   // system
+  int chans;
   DivSystem system[DIV_MAX_CHIPS];
   unsigned short systemChans[DIV_MAX_CHIPS];
   unsigned char systemLen;
@@ -396,10 +397,17 @@ struct DivSong {
   DivWavetable nullWave;
   DivSample nullSample;
 
+  DivSystem sysOfChan[DIV_MAX_CHANS];
+  int dispatchOfChan[DIV_MAX_CHANS];
+  int dispatchChanOfChan[DIV_MAX_CHANS];
+  int dispatchFirstChan[DIV_MAX_CHANS];
+
+  std::vector<DivInstrumentType> possibleInsTypes;
+
   /**
    * find data past 0Bxx effects and place that into new sub-songs.
    */
-  void findSubSongs(int chans);
+  void findSubSongs();
 
   /**
    * clear orders and patterns.
@@ -421,6 +429,12 @@ struct DivSong {
    */
   void clearSamples();
 
+  /**
+   * recalculate channel count and internal state.
+   " call after editing system[] or systemChans[].
+   */
+  void recalcChans();
+
   /**
    * unloads the song, freeing all memory associated with it.
    * use before destroying the object.
@@ -430,6 +444,7 @@ struct DivSong {
   DivSong():
     version(0),
     isDMF(false),
+    chans(0),
     systemLen(2),
     name(""),
     author(""),
@@ -508,6 +523,11 @@ struct DivSong {
     oldAlwaysSetVolume(false),
     oldSampleOffset(false),
     oldCenterRate(true) {
+    memset(dispatchFirstChan,0,DIV_MAX_CHANS*sizeof(int));
+    memset(dispatchChanOfChan,0,DIV_MAX_CHANS*sizeof(int));
+    memset(dispatchOfChan,0,DIV_MAX_CHANS*sizeof(int));
+    memset(sysOfChan,0,DIV_MAX_CHANS*sizeof(int));
+
     for (int i=0; i<DIV_MAX_CHIPS; i++) {
       system[i]=DIV_SYSTEM_NULL;
       systemChans[i]=0;
@@ -654,6 +674,8 @@ struct DivSong {
     nullInsESFM.fm.op[3].sl=15;
     nullInsESFM.fm.op[3].rr=9;
     nullInsESFM.fm.op[3].mult=1;
+
+    recalcChans();
   }
 };