diff --git a/plugin/module.hpp b/plugin/module.hpp
index 428fe41..6ba1b3c 100644
--- a/plugin/module.hpp
+++ b/plugin/module.hpp
@@ -75,6 +75,10 @@ class Voice {
     float delay = 0, lastpw = 0;  // delay slots for antialiasing
     uint8_t pulseStage = 1;       // pulse wave phase
     float subosc = 1;             // sub oscillator flipflop output
+
+    // filter
+    float b1=0, b2=0, b3=0, b4=0;
 };
 
+
 #endif
\ No newline at end of file
diff --git a/plugin/voice.cpp b/plugin/voice.cpp
index 4087063..abf1d62 100644
--- a/plugin/voice.cpp
+++ b/plugin/voice.cpp
@@ -49,8 +49,9 @@ void Voice::off() {
 
 void Voice::run(Module* m, float* buffer, uint32_t samples) {
     // carry out per-voice calculations for each block of samples
-    float out, t;
+    float out, t, fb, res;
 
+    float cut = 0.00513 + 0.075*env;
     // printf("%f ", delay);
     m->saw = 1;
     m->square = 1;
@@ -92,7 +93,20 @@ void Voice::run(Module* m, float* buffer, uint32_t samples) {
         delay += m->sub * subosc;
         // delay += (1-(m->noisegen/(float)(1<<30))) * m->noise; FIXME figure out what to do about noise
 
-        buffer[i] += 0.125 * env * out;
+        for (uint8_t ovs = 0; ovs < 4; ovs++) {
+            fb = b4;
+            // hard clip
+            if (fb > 1) fb = 1;
+            if (fb < -1) fb = -1;
+
+            fb = out - (fb * 2);
+            b1 = ((fb - b1) * cut) + b1;
+            b2 = ((b1 - b2) * cut) + b2;
+            b3 = ((b2 - b3) * cut) + b3;
+            b4 = ((b3 - b4) * cut) + b4;
+        }
+
+        buffer[i] += 0.125 * env * b4;
         lastpw = m->pw;
     }
     // buffer[0] += 1;