diff --git a/README.md b/README.md
index 64c9d25..da79571 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,7 @@ Changelog
 #### Version 0.9.2
 * Added operator mute switch
 * Added Tune (MASTER TUNE ADJ) knob
+* Correct feedback implementation for Algo 4 and 6
 * Single click program select
 * Fix sysex issue with wrong machine ID
 
diff --git a/Source/DXComponents.h b/Source/DXComponents.h
index 2dd415f..cf75638 100644
--- a/Source/DXComponents.h
+++ b/Source/DXComponents.h
@@ -63,7 +63,7 @@ class ComboBoxImage : public ComboBox {
 public:
     ComboBoxImage();
 
-    virtual void paint(Graphics &g);
+    virtual void paint(Graphics &g) override;
     virtual void showPopup() override;
     void setImage(Image image);
     void setImage(Image image, int pos[]);
diff --git a/Source/DXLookNFeel.h b/Source/DXLookNFeel.h
index dccc812..85f5dc6 100644
--- a/Source/DXLookNFeel.h
+++ b/Source/DXLookNFeel.h
@@ -39,8 +39,8 @@ public:
     Image imageOperator, imageGlobal;
 
     /* overriden methods */
-    virtual void drawRotarySlider(Graphics &g, int x, int y, int width, int height, float sliderPosProportional, float rotaryStartAngle, float rotaryEndAngle,  Slider &slider );
-    virtual void drawToggleButton(Graphics& g, ToggleButton& button, bool isMouseOverButton, bool isButtonDown);
+    virtual void drawRotarySlider(Graphics &g, int x, int y, int width, int height, float sliderPosProportional, float rotaryStartAngle, float rotaryEndAngle,  Slider &slider ) override;
+    virtual void drawToggleButton(Graphics& g, ToggleButton& button, bool isMouseOverButton, bool isButtonDown) override;
     virtual void drawLinearSliderBackground (Graphics&, int x, int y, int width, int height,
                                      float sliderPos, float minSliderPos, float maxSliderPos,
                                      const Slider::SliderStyle, Slider&) override;
@@ -50,8 +50,8 @@ public:
     virtual void drawButtonBackground (Graphics&, Button&, const Colour& backgroundColour,
                                bool isMouseOverButton, bool isButtonDown) override;
     virtual Font getTextButtonFont(TextButton&, int buttonHeight) override;
-    virtual Typeface::Ptr getTypefaceForFont(const Font &);
-    virtual void positionComboBoxText (ComboBox& box, Label& label);
+    virtual Typeface::Ptr getTypefaceForFont(const Font &) override;
+    virtual void positionComboBoxText (ComboBox& box, Label& label) override;
 
     static DXLookNFeel *getLookAndFeel();
     static Colour fillColour;
diff --git a/Source/EngineMkI.cpp b/Source/EngineMkI.cpp
index 83dea2e..83737fa 100644
--- a/Source/EngineMkI.cpp
+++ b/Source/EngineMkI.cpp
@@ -57,6 +57,8 @@ static const uint16_t SINEXP_BITDEPTH = 10;
 static const uint16_t SINEXP_TABLESIZE = 1<<SINEXP_BITDEPTH;
 static uint16_t sinExpTable[SINEXP_TABLESIZE];
 
+const uint16_t ENV_MAX = 1<<ENV_BITDEPTH;
+
 static inline uint16_t sinLog(uint16_t phi) {
     const uint16_t SINLOG_TABLEFILTER = SINLOG_TABLESIZE-1;
     const uint16_t index = (phi & SINLOG_TABLEFILTER);
@@ -200,183 +202,105 @@ void EngineMkI::compute_fb(int32_t *output, int32_t phase0, int32_t freq,
     fb_buf[1] = y;
 }
 
-/*
-void EngineMkI::render(int32_t *output, FmOpParams *params, int algorithm,
-                       int32_t *fb_buf, int feedback_shift) {
-    const uint16_t ENV_MAX = 1<<ENV_BITDEPTH;
-    const uint16_t kLevelThresh = ENV_MAX-100;  // really ???? uhuhuh
-    const FmAlgorithm alg = algorithms[algorithm];
-    bool has_contents[3] = { true, false, false };
-    for (int op = 0; op < 6; op++) {
-        int flags = alg.ops[op];
-        bool add = (flags & OUT_BUS_ADD) != 0;
-        FmOpParams &param = params[op];
-        int inbus = (flags >> 4) & 3;
-        int outbus = flags & 3;
-        int32_t *outptr = (outbus == 0) ? output : buf_[outbus - 1].get();
-        int32_t gain1 = param.gain_out == 0 ? (ENV_MAX-1) : param.gain_out;
-        int32_t gain2 = ENV_MAX-(param.level_in >> (28-ENV_BITDEPTH));
-        param.gain_out = gain2;
-
-        if (gain1 <= kLevelThresh || gain2 <= kLevelThresh) {
-            if (!has_contents[outbus]) {
-                add = false;
-            }
-            if (inbus == 0 || !has_contents[inbus]) {
-                // todo: more than one op in a feedback loop
-                if ((flags & 0xc0) == 0xc0 && feedback_shift < 16) {
-                    // cout << op << " fb " << inbus << outbus << add << endl;
-                    compute_fb(outptr, param.phase, param.freq,
-                               gain1, gain2,
-                               fb_buf, feedback_shift, add);
-                } else {
-                    // cout << op << " pure " << inbus << outbus << add << endl;
-                    compute_pure(outptr, param.phase, param.freq,
-                                 gain1, gain2, add);
-                }
-            } else {
-                // cout << op << " normal " << inbus << outbus << " " << param.freq << add << endl;
-                compute(outptr, buf_[inbus - 1].get(),
-                        param.phase, param.freq, gain1, gain2, add);
-            }
-            has_contents[outbus] = true;
-        } else if (!add) {
-            has_contents[outbus] = false;
-        }
-        param.phase += param.freq << LG_N;
-    }
-}
-*/
-
-const FmAlgorithm EngineMkI::algo2[32] = {
-    { { 0xc1, 0x11, 0x11, 0x14, 0x01, 0x14 } }, // 1
-    { { 0x01, 0x11, 0x11, 0x14, 0xc1, 0x14 } }, // 2
-    { { 0xc1, 0x11, 0x14, 0x01, 0x11, 0x14 } }, // 3
-    { { 0xc4, 0x00, 0x00, 0x01, 0x11, 0x14 } }, // 4 ** EXCEPTION VIA CODE
-    { { 0xc1, 0x14, 0x01, 0x14, 0x01, 0x14 } }, // 5
-    { { 0xc4, 0x00, 0x01, 0x14, 0x01, 0x14 } }, // 6 ** EXCEPTION VIA CODE
-    { { 0xc1, 0x11, 0x05, 0x14, 0x01, 0x14 } }, // 7
-    { { 0x01, 0x11, 0xc5, 0x14, 0x01, 0x14 } }, // 8
-    { { 0x01, 0x11, 0x05, 0x14, 0xc1, 0x14 } }, // 9
-    { { 0x01, 0x05, 0x14, 0xc1, 0x11, 0x14 } }, // 10
-    { { 0xc1, 0x05, 0x14, 0x01, 0x11, 0x14 } }, // 11
-    { { 0x01, 0x05, 0x05, 0x14, 0xc1, 0x14 } }, // 12
-    { { 0xc1, 0x05, 0x05, 0x14, 0x01, 0x14 } }, // 13
-    { { 0xc1, 0x05, 0x11, 0x14, 0x01, 0x14 } }, // 14
-    { { 0x01, 0x05, 0x11, 0x14, 0xc1, 0x14 } }, // 15
-    { { 0xc1, 0x11, 0x02, 0x25, 0x05, 0x14 } }, // 16
-    { { 0x01, 0x11, 0x02, 0x25, 0xc5, 0x14 } }, // 17
-    { { 0x01, 0x11, 0x11, 0xc5, 0x05, 0x14 } }, // 18
-    { { 0xc1, 0x14, 0x14, 0x01, 0x11, 0x14 } }, // 19
-    { { 0x01, 0x05, 0x14, 0xc1, 0x14, 0x14 } }, // 20
-    { { 0x01, 0x14, 0x14, 0xc1, 0x14, 0x14 } }, // 21
-    { { 0xc1, 0x14, 0x14, 0x14, 0x01, 0x14 } }, // 22
-    { { 0xc1, 0x14, 0x14, 0x01, 0x14, 0x04 } }, // 23
-    { { 0xc1, 0x14, 0x14, 0x14, 0x04, 0x04 } }, // 24
-    { { 0xc1, 0x14, 0x14, 0x04, 0x04, 0x04 } }, // 25
-    { { 0xc1, 0x05, 0x14, 0x01, 0x14, 0x04 } }, // 26
-    { { 0x01, 0x05, 0x14, 0xc1, 0x14, 0x04 } }, // 27
-    { { 0x04, 0xc1, 0x11, 0x14, 0x01, 0x14 } }, // 28
-    { { 0xc1, 0x14, 0x01, 0x14, 0x04, 0x04 } }, // 29
-    { { 0x04, 0xc1, 0x11, 0x14, 0x04, 0x04 } }, // 30
-    { { 0xc1, 0x14, 0x04, 0x04, 0x04, 0x04 } }, // 31
-    { { 0xc4, 0x04, 0x04, 0x04, 0x04, 0x04 } }, // 32
-};
-
-// exclusively used for ALGO 4 with feedback
-void EngineMkI::compute_fb3(int32_t *output, FmOpParams *parms, int32_t gain01, int32_t gain02, int32_t *fb_buf, int fb_shift) {
-    int32_t dgain[3];
-    int32_t gain[3];
-    int32_t phase[3];
+// exclusively used for ALGO 6 with feedback
+void EngineMkI::compute_fb2(int32_t *output, FmOpParams *parms, int32_t gain01, int32_t gain02, int32_t *fb_buf, int fb_shift) {
+    int32_t dgain[2];
+    int32_t gain[2];
+    int32_t phase[2];
     int32_t y0 = fb_buf[0];
     int32_t y = fb_buf[1];
     
     phase[0] = parms[0].phase;
     phase[1] = parms[1].phase;
-    phase[2] = parms[2].phase;
-    
+
+    parms[1].gain_out = (ENV_MAX-(parms[1].level_in >> (28-ENV_BITDEPTH)));
+
     gain[0] = gain01;
-    gain[1] = parms[1].gain_out;
-    gain[2] = parms[2].gain_out;
-    
+    gain[1] = parms[1].gain_out == 0 ? (ENV_MAX-1) : parms[1].gain_out;
+
     dgain[0] = (gain02 - gain01 + (N >> 1)) >> LG_N;
-    
-    parms[1].gain_out = Exp2::lookup(parms[1].level_in - (14 * (1 << 24)));
-    dgain[1] = (parms[1].gain_out - gain[1] + (N >> 1)) >> LG_N;
-    parms[2].gain_out = Exp2::lookup(parms[2].level_in - (14 * (1 << 24)));
-    dgain[2] = (parms[1].gain_out - gain[2] + (N >> 1)) >> LG_N;
+    dgain[1] = (parms[1].gain_out - (parms[1].gain_out == 0 ? (ENV_MAX-1) : parms[1].gain_out));
     
     for (int i = 0; i < N; i++) {
+        int32_t scaled_fb = (y0 + y) >> (fb_shift + 1);
+        
         // op 0
         gain[0] += dgain[0];
-        int32_t scaled_fb = (y0 + y) >> (fb_shift + 1);     // tsk tsk tsk: this needs some tuning
         y0 = y;
-        y = Sin::lookup(phase[0] + scaled_fb);
-        y = ((int64_t)y * (int64_t)gain[0]) >> 24;
+        y = mkiSin(phase[0]+scaled_fb, gain[0]);
         phase[0] += parms[0].freq;
         
         // op 1
         gain[1] += dgain[1];
-        y = Sin::lookup(phase[1] + y);
-        y = ((int64_t)y * (int64_t)gain[1]) >> 24;
+        y = mkiSin(phase[1]+y, gain[1]);
         phase[1] += parms[1].freq;
         
-        // op 2
-        gain[2] += dgain[2];
-        y = Sin::lookup(phase[2] + y);
-        y = ((int64_t)y * (int64_t)gain[2]) >> 24;
         output[i] = y;
-        phase[2] += parms[2].freq;
     }
     fb_buf[0] = y0;
     fb_buf[1] = y;
 }
 
-// exclusively used for ALGO 6 with feedback
-void EngineMkI::compute_fb2(int32_t *output, FmOpParams *parms, int32_t gain01, int32_t gain02, int32_t *fb_buf, int fb_shift) {
-    int32_t dgain[2];
-    int32_t gain[2];
-    int32_t phase[2];
+// exclusively used for ALGO 4 with feedback
+void EngineMkI::compute_fb3(int32_t *output, FmOpParams *parms, int32_t gain01, int32_t gain02, int32_t *fb_buf, int fb_shift) {
+    int32_t dgain[3];
+    int32_t gain[3];
+    int32_t phase[3];
     int32_t y0 = fb_buf[0];
     int32_t y = fb_buf[1];
     
     phase[0] = parms[0].phase;
     phase[1] = parms[1].phase;
+    phase[2] = parms[2].phase;
     
-    gain[0] = gain01;
-    gain[1] = parms[1].gain_out;
+    parms[1].gain_out = (ENV_MAX-(parms[1].level_in >> (28-ENV_BITDEPTH)));
+    parms[2].gain_out = (ENV_MAX-(parms[2].level_in >> (28-ENV_BITDEPTH)));
     
+    gain[0] = gain01;
+    gain[1] = parms[1].gain_out == 0 ? (ENV_MAX-1) : parms[1].gain_out;
+    gain[2] = parms[2].gain_out == 0 ? (ENV_MAX-1) : parms[2].gain_out;
+
     dgain[0] = (gain02 - gain01 + (N >> 1)) >> LG_N;
+    dgain[1] = (parms[1].gain_out - (parms[1].gain_out == 0 ? (ENV_MAX-1) : parms[1].gain_out));
+    dgain[2] = (parms[2].gain_out - (parms[2].gain_out == 0 ? (ENV_MAX-1) : parms[2].gain_out));
     
-    parms[1].gain_out = Exp2::lookup(parms[1].level_in - (14 * (1 << 24)));
-    dgain[1] = (parms[1].gain_out - gain[1] + (N >> 1)) >> LG_N;
     
     for (int i = 0; i < N; i++) {
+        int32_t scaled_fb = (y0 + y) >> (fb_shift + 1);
+        
         // op 0
         gain[0] += dgain[0];
-        int32_t scaled_fb = (y0 + y) >> (fb_shift + 1); 
         y0 = y;
-        y = Sin::lookup(phase[0] + scaled_fb);
-        y = ((int64_t)y * (int64_t)gain[0]) >> 24;
+        y = mkiSin(phase[0]+scaled_fb, gain[0]);
         phase[0] += parms[0].freq;
         
         // op 1
         gain[1] += dgain[1];
-        y = Sin::lookup(phase[1] + y);
-        y = ((int64_t)y * (int64_t)gain[1]) >> 24;
-        output[i] = y;
+        y = mkiSin(phase[1]+y, gain[1]);
         phase[1] += parms[1].freq;
+        
+        // op 2
+        gain[2] += dgain[2];
+        y = mkiSin(phase[2]+y, gain[2]);
+        phase[2] += parms[2].freq;
+        
+        output[i] = y;
     }
     fb_buf[0] = y0;
     fb_buf[1] = y;
 }
 
-
 void EngineMkI::render(int32_t *output, FmOpParams *params, int algorithm, int32_t *fb_buf, int feedback_shift) {
-    const uint16_t ENV_MAX = 1<<ENV_BITDEPTH;
     const int kLevelThresh = ENV_MAX-100;
-    const FmAlgorithm alg = algo2[algorithm];
+    FmAlgorithm alg = algorithms[algorithm];
     bool has_contents[3] = { true, false, false };
+    bool fb_on = feedback_shift < 16;
+
+    switch(algorithm) {
+        case 3 : case 5 :
+            if ( fb_on )
+                alg.ops[0] = 0xc4;
+    }
     
     for (int op = 0; op < 6; op++) {
         int flags = alg.ops[op];
@@ -397,15 +321,8 @@ void EngineMkI::render(int32_t *output, FmOpParams *params, int algorithm, int32
             
             if (inbus == 0 || !has_contents[inbus]) {
                 // PG: this is my 'dirty' implementation of FB for 2 and 3 operators...
-                // still needs some tuning...
-                if ((flags & 0xc0) == 0xc0 && feedback_shift < 16) {
+                if ((flags & 0xc0) == 0xc0 && fb_on) {
                     switch ( algorithm ) {
-                        // two operator feedback, process exception for ALGO 6
-                        case 5 :
-                            compute_fb2(outptr, params, gain1, gain2, fb_buf, feedback_shift);
-                            params[1].phase += params[1].freq << LG_N;  // yuk, hack, we already processed op-5
-                            op++; // ignore next operator;
-                            break;
                         // three operator feedback, process exception for ALGO 4
                         case 3 :
                             compute_fb3(outptr, params, gain1, gain2, fb_buf, feedback_shift);
@@ -413,24 +330,25 @@ void EngineMkI::render(int32_t *output, FmOpParams *params, int algorithm, int32
                             params[2].phase += params[2].freq << LG_N; // yuk yuk
                             op += 2; // ignore the 2 other operators
                             break;
+                        // two operator feedback, process exception for ALGO 6
+                        case 5 :
+                            compute_fb2(outptr, params, gain1, gain2, fb_buf, feedback_shift);
+                            params[1].phase += params[1].freq << LG_N;  // yuk, hack, we already processed op-5
+                            op++; // ignore next operator;
+                            break;
                         default:
                             // one operator feedback, normal proces
-                            //cout << "\t" << op << " fb " << inbus << outbus << add << endl;
-                            compute_fb(outptr, param.phase, param.freq,gain1, gain2, fb_buf, feedback_shift, add);
+                            compute_fb(outptr, param.phase, param.freq, gain1, gain2, fb_buf, feedback_shift, add);
                             break;
                     }
                 } else {
-                    // cout << op << " pure " << inbus << outbus << add << endl;
                     compute_pure(outptr, param.phase, param.freq, gain1, gain2, add);
                 }
             } else {
-                
-                // cout << op << " normal " << inbus << outbus << " " << param.freq << add << endl;
                 compute(outptr, buf_[inbus - 1].get(), param.phase, param.freq, gain1, gain2, add);
             }
             
             has_contents[outbus] = true;
-            
         } else if (!add) {
             has_contents[outbus] = false;
         }
diff --git a/Source/EngineMkI.h b/Source/EngineMkI.h
index 8478b90..9f355fe 100644
--- a/Source/EngineMkI.h
+++ b/Source/EngineMkI.h
@@ -26,8 +26,6 @@
 
 
 class EngineMkI : public FmCore {
-    //refacter this when it is working
-    const static FmAlgorithm algo2[32];
 public:
     EngineMkI();
     
diff --git a/Source/OperatorEditor.h b/Source/OperatorEditor.h
index 99a1b5f..48c9540 100644
--- a/Source/OperatorEditor.h
+++ b/Source/OperatorEditor.h
@@ -56,10 +56,10 @@ public:
     void mouseDown(const MouseEvent& e) override;
     //[/UserMethods]
 
-    void paint (Graphics& g);
-    void resized();
-    void sliderValueChanged (Slider* sliderThatWasMoved);
-    void buttonClicked (Button* buttonThatWasClicked);
+    void paint (Graphics& g) override;
+    void resized() override;
+    void sliderValueChanged (Slider* sliderThatWasMoved) override;
+    void buttonClicked (Button* buttonThatWasClicked) override;
 
 
 
diff --git a/Source/msfa/fm_core.cc b/Source/msfa/fm_core.cc
index b083ab3..408d0de 100644
--- a/Source/msfa/fm_core.cc
+++ b/Source/msfa/fm_core.cc
@@ -30,9 +30,9 @@ const FmAlgorithm FmCore::algorithms[32] = {
   { { 0xc1, 0x11, 0x11, 0x14, 0x01, 0x14 } }, // 1
   { { 0x01, 0x11, 0x11, 0x14, 0xc1, 0x14 } }, // 2
   { { 0xc1, 0x11, 0x14, 0x01, 0x11, 0x14 } }, // 3
-  { { 0xc1, 0x11, 0x94, 0x01, 0x11, 0x14 } }, // 4 ** EXCEPTION VIA CODE
+  { { 0xc1, 0x11, 0x94, 0x01, 0x11, 0x14 } }, // 4
   { { 0xc1, 0x14, 0x01, 0x14, 0x01, 0x14 } }, // 5
-  { { 0xc1, 0x94, 0x01, 0x14, 0x01, 0x14 } }, // 6 ** EXCEPTION VIA CODE
+  { { 0xc1, 0x94, 0x01, 0x14, 0x01, 0x14 } }, // 6
   { { 0xc1, 0x11, 0x05, 0x14, 0x01, 0x14 } }, // 7
   { { 0x01, 0x11, 0xc5, 0x14, 0x01, 0x14 } }, // 8
   { { 0x01, 0x11, 0x05, 0x14, 0xc1, 0x14 } }, // 9