diff --git a/src/engine/dispatch.h b/src/engine/dispatch.h
index b358c464c..bd3b19a68 100644
--- a/src/engine/dispatch.h
+++ b/src/engine/dispatch.h
@@ -426,7 +426,8 @@ class DivDispatch {
 #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 NOTE_FNUM_BLOCK(x,bits) ((((int)parent->calcBaseFreq(chipClock,CHIP_FREQBASE,(x)%12,false))&((1<<bits)-1))|((MAX(x,0)/12)<<bits))
+
+#define NOTE_FNUM_BLOCK(x,bits) parent->calcBaseFreqFNumBlock(chipClock,CHIP_FREQBASE,x,bits)
 
 #define COLOR_NTSC (315000000.0/88.0)
 #define COLOR_PAL (283.75*15625.0+25.0)
diff --git a/src/engine/engine.cpp b/src/engine/engine.cpp
index 905ba8aa5..2ebbd2fdb 100644
--- a/src/engine/engine.cpp
+++ b/src/engine/engine.cpp
@@ -887,6 +887,17 @@ double DivEngine::calcBaseFreq(double clock, double divider, int note, bool peri
          base*(divider/clock);
 }
 
+unsigned short DivEngine::calcBaseFreqFNumBlock(double clock, double divider, int note, int bits) {
+  int bf=calcBaseFreq(clock,divider,note,false);
+  int block=note/12;
+  if (block<0) block=0;
+  if (block>7) block=7;
+  bf>>=block;
+  if (bf<0) bf=0;
+  if (bf>((1<<bits)-1)) bf=(1<<bits)-1;
+  return bf|(block<<bits);
+}
+
 int DivEngine::calcFreq(int base, int pitch, bool period, int octave) {
   if (song.linearPitch) {
     // global pitch multiplier
diff --git a/src/engine/engine.h b/src/engine/engine.h
index 3bd1db3dc..57acf970d 100644
--- a/src/engine/engine.h
+++ b/src/engine/engine.h
@@ -367,6 +367,9 @@ class DivEngine {
     // calculate base frequency/period
     double calcBaseFreq(double clock, double divider, int note, bool period);
 
+    // calculate base frequency in f-num/block format
+    unsigned short calcBaseFreqFNumBlock(double clock, double divider, int note, int bits);
+
     // calculate frequency/period
     int calcFreq(int base, int pitch, bool period=false, int octave=0);