diff --git a/makefile b/makefile
index cc53ac6..f4f9516 100644
--- a/makefile
+++ b/makefile
@@ -1,4 +1,4 @@
-CFLAGS = -fPIC
+CFLAGS = -O3 -fPIC
 FLAGS = -shared
 TARGET = libsynth.so
 
diff --git a/synth.c b/synth.c
index 06515a2..85442c0 100644
--- a/synth.c
+++ b/synth.c
@@ -6,7 +6,13 @@ typedef double             D;
 #define DO(n,stm) {I i=0,_n=(n); for(;i<_n;i++){stm}}
 #define DECL_ARR(t, v, l) t *v = malloc(sizeof(t)*(l))
 
+void filter11(I,D*,D,D);
+void filter21(I,D*,D,D,D);
+void filter32(I,D*,D,D,D,D,D);
 void filter(I length, D* a, I lx, D* xc, I ly, D* yc) {
+    if (lx==1 && ly==1) { return filter11(length,a,xc[0],yc[0]); }
+    if (lx==2 && ly==1) { return filter21(length,a,xc[0],xc[1],yc[0]); }
+    if (lx==3 && ly==2) { return filter32(length,a,xc[0],xc[1],xc[2],yc[0],yc[1]); }
     DECL_ARR(D, x, lx); DECL_ARR(D, y, ly);
     DO(lx, x[i]=0;); DO(ly, y[i]=0;);
     int j, ix=0, iy=0;
@@ -17,6 +23,35 @@ void filter(I length, D* a, I lx, D* xc, I ly, D* yc) {
         DO(ly, a[j] += y[(iy+i)%ly] * yc[i];);
         y[iy++] = a[j]; iy%=ly;
     }
+    free(x); free(y);
+    return;
+}
+
+void filter11(I length, D* a, D xc0, D yc0) {
+    D x0=0, y0=0; int j;
+    for (j=0; j<length; j++) {
+        x0 = a[j];
+        a[j] = x0*xc0 + y0*yc0;
+        y0 = a[j];
+    }
+    return;
+}
+void filter21(I length, D* a, D xc0, D xc1, D yc0) {
+    D x0=0, x1=0, y0=0; int j;
+    for (j=0; j<length; j++) {
+        x0 = x1; x1 = a[j];
+        a[j] = x0*xc0 + x1*xc1 + y0*yc0;
+        y0 = a[j];
+    }
+    return;
+}
+void filter32(I length, D* a, D xc0, D xc1, D xc2, D yc0, D yc1) {
+    D x0=0, x1=0, x2=0, y0=0, y1=0; int j;
+    for (j=0; j<length; j++) {
+        x0 = x1; x1 = x2; x2 = a[j];
+        a[j] = x0*xc0 + x1*xc1 + x2*xc2 + y0*yc0 + y1*yc1;
+        y0 = y1; y1 = a[j];
+    }
     return;
 }