diff --git a/crap_delay_test.h b/crap_delay_test.h
index 6bec086..378b3df 100644
--- a/crap_delay_test.h
+++ b/crap_delay_test.h
@@ -126,7 +126,7 @@ adjust(personal *data, ulong fs) {
 			c->up[i] = 0;
 		for (int i = 0; i < DOWN; i++)
 			c->down[i] = 0;
-		c->filter = biquad_gen(0, 16630, 10, 1, fs*oversample);
+		c->filter = biquad_gen(FILT_PEAKING, 16630, 10, 1, fs*oversample);
 		biquad_init(&c->filter);
 	}
 }
diff --git a/crap_eq.h b/crap_eq.h
old mode 100755
new mode 100644
index ee125dc..8772bf6
--- a/crap_eq.h
+++ b/crap_eq.h
@@ -79,8 +79,8 @@ construct_params(param *params) {
 		param_reset(&params[1]);
 
 		sprintf(params[2].name, "Band %i Bandwidth", i + 1);
-		params[2].min = 0.0625;
-		params[2].max = 8;
+		params[2].min = 0.0625; // 2^-4 could probably be 2^-3
+		params[2].max = 8;      // 2^3  could probably be 2^2
 		params[2].scale = SCALE_FLOAT;
 		params[2].def = DEFAULT_1;
 		param_reset(&params[2]);
@@ -102,7 +102,7 @@ adjust(personal *data, param *params, unsigned long fs) {
 	data->fs = fs;
 	biquad *filters = data->filters[0];
 	for (int i = 0; i < BANDS; i++) {
-		filters[i] = biquad_gen(0,
+		filters[i] = biquad_gen(FILT_PEAKING,
 		    params[0].value, params[1].value, params[2].value, fs);
 		params += 3;
 	}
@@ -113,7 +113,7 @@ static void
 adjust_one(personal *data, param *params, unsigned int index) {
 	float fs = data->fs;
 	params += index/3*3;
-	data->filters[0][index/3] = biquad_gen(0,
+	data->filters[0][index/3] = biquad_gen(FILT_PEAKING,
 	    params[0].value, params[1].value, params[2].value, fs);
 	resume(data);
 }
diff --git a/crap_eq_const.h b/crap_eq_const.h
index 7a9c7f6..53b9784 100644
--- a/crap_eq_const.h
+++ b/crap_eq_const.h
@@ -69,8 +69,8 @@ pause(personal *data) {
 static void
 adjust(personal *data, unsigned long fs) {
 	biquad *filters = data->filters[0];
-	filters[0] = biquad_gen(0, 34.34, +4.6, 1.21, fs);
-	filters[1] = biquad_gen(0, 85.74, -1.2, 1.31, fs);
-	filters[2] = biquad_gen(2, 862.2, -5.5, 1.00, fs);
-	filters[3] = biquad_gen(0, 7496., +3.3, 1.10, fs);
+	filters[0] = biquad_gen(FILT_PEAKING,   34.34, +4.6, 1.21, fs);
+	filters[1] = biquad_gen(FILT_PEAKING,   85.74, -1.2, 1.31, fs);
+	filters[2] = biquad_gen(FILT_HIGHSHELF, 862.2, -5.5, 1.00, fs);
+	filters[3] = biquad_gen(FILT_PEAKING,   7496., +3.3, 1.10, fs);
 }
diff --git a/crap_util.h b/crap_util.h
index 3d84d2d..98f8732 100644
--- a/crap_util.h
+++ b/crap_util.h
@@ -29,20 +29,21 @@ whitenoise();
 static void
 biquad_init(biquad *bq);
 
-/* types: TODO: enum
- 0: peaking
- 1: lowshelf
- 2: highshelf
- 3: lowpass
- 4: highpass
- 5: allpass
- 6: bandpass 1
- 7: bandpass 2
- 8: notch
- 9: gain
-*/
+typedef enum {
+	FILT_PEAKING,
+	FILT_LOWSHELF,
+	FILT_HIGHSHELF,
+	FILT_LOWPASS,
+	FILT_HIGHPASS,
+	FILT_ALLPASS,
+	FILT_BANDPASS,
+	FILT_BANDPASS_2,
+	FILT_NOTCH,
+	FILT_GAIN
+} filter_t;
+
 static biquad
-biquad_gen(int type, double fc, double gain, double bw, double fs);
+biquad_gen(filter_t type, double fc, double gain, double bw, double fs);
 
 /* s-plane to z-plane */
 static biquad_interim
diff --git a/crap_util_def.h b/crap_util_def.h
index 7e9bd33..76aa22f 100644
--- a/crap_util_def.h
+++ b/crap_util_def.h
@@ -38,29 +38,32 @@ design(double cw, double sw,
 }
 
 static biquad
-biquad_gen(int type, double fc, double gain, double bw, double fs) {
+biquad_gen(filter_t type, double fc, double gain, double bw, double fs) {
 	double w0, cw, sw, A, As, Q;
 	w0 = ANGULAR_LIM(fc, fs);
 	cw = cos(w0);
 	sw = sin(w0);
 	A = DB2LIN(gain/2);
 	As = sqrt(A);
-	Q = 1/(4*sinh(M_LN2/2*bw*w0/sw));
-	//Q = M_SQRT1_2*(1 - SQR(w0/M_PI))/bw;
+	Q = M_SQRT1_2*(1 - (w0/M_PI)*(w0/M_PI))/bw;
 	/* skip = (fabs(A - 1) <= TINY); */
 
-	/* TODO: use enum for type instead of just int */
 	biquad_interim bqi;
-	if (type == 0) bqi = design(cw,sw, 1,  A/Q, 1,   1,  1/A/Q,   1);
-	if (type == 1) bqi = design(cw,sw, 1, As/Q, A,   1, 1/As/Q, 1/A);
-	if (type == 2) bqi = design(cw,sw, A, As/Q, 1, 1/A, 1/As/Q,   1);
-	if (type == 3) bqi = design(cw,sw, 0,    0, 1,   1,    1/Q,   1);
-	if (type == 4) bqi = design(cw,sw, 1,    0, 0,   1,    1/Q,   1);
-	if (type == 5) bqi = design(cw,sw, 1, -1/Q, 1,   1,    1/Q,   1);
-	if (type == 6) bqi = design(cw,sw, 0,    1, 0,   1,    1/Q,   1);
-	if (type == 7) bqi = design(cw,sw, 0,  1/Q, 0,   1,    1/Q,   1);
-	if (type == 8) bqi = design(cw,sw, 1,    0, 1,   1,    1/Q,   1);
-	if (type == 9) bqi = design(cw,sw, A,    A, A, 1/A,    1/A, 1/A);
+
+	#define d(n0,n1,n2,d0,d1,d2) bqi = design(cw,sw,n0,n1,n2,d0,d1,d2)
+	switch (type) {
+	case FILT_PEAKING:    d(1,  A/Q, 1,   1,  1/A/Q,   1); break;
+	case FILT_LOWSHELF:   d(1, As/Q, A,   1, 1/As/Q, 1/A); break;
+	case FILT_HIGHSHELF:  d(A, As/Q, 1, 1/A, 1/As/Q,   1); break;
+	case FILT_LOWPASS:    d(0,    0, 1,   1,    1/Q,   1); break;
+	case FILT_HIGHPASS:   d(1,    0, 0,   1,    1/Q,   1); break;
+	case FILT_ALLPASS:    d(1, -1/Q, 1,   1,    1/Q,   1); break;
+	case FILT_BANDPASS:   d(0,    1, 0,   1,    1/Q,   1); break;
+	case FILT_BANDPASS_2: d(0,  1/Q, 0,   1,    1/Q,   1); break;
+	case FILT_NOTCH:      d(1,    0, 1,   1,    1/Q,   1); break;
+	case FILT_GAIN:       d(A,    A, A, 1/A,    1/A, 1/A); break;
+	}
+	#undef d
 
 	double a0r = 1/bqi.a0;