diff --git a/src/libfilter/iir_filter.c b/src/libfilter/iir_filter.c
index 5872d61..2749f96 100644
--- a/src/libfilter/iir_filter.c
+++ b/src/libfilter/iir_filter.c
@@ -88,13 +88,12 @@ void iir_bandpass_init(iir_filter_t *filter, double frequency, int samplerate, i
 	filter->b2 = (1 - K / Q + K * K) * norm;
 }
 
-void iir_notch_init(iir_filter_t *filter, double frequency, int samplerate, int iterations)
+void iir_notch_init(iir_filter_t *filter, double frequency, int samplerate, int iterations, double Q)
 {
-	double Fc, Q, K, norm;
+	double Fc, K, norm;
 
 	memset(filter, 0, sizeof(*filter));
 	filter->iter = iterations;
-	Q = pow(sqrt(0.5), 1.0 / (double)iterations); /* 0.7071 @ 1 iteration */
 	Fc = frequency / (double)samplerate;
 	K = tan(PI * Fc);
 	norm = 1 / (1 + K / Q + K * K);
diff --git a/src/libfilter/iir_filter.h b/src/libfilter/iir_filter.h
index a5956c8..9b2d7ce 100644
--- a/src/libfilter/iir_filter.h
+++ b/src/libfilter/iir_filter.h
@@ -10,7 +10,7 @@ typedef struct iir_filter {
 void iir_lowpass_init(iir_filter_t *filter, double frequency, int samplerate, int iterations);
 void iir_highpass_init(iir_filter_t *filter, double frequency, int samplerate, int iterations);
 void iir_bandpass_init(iir_filter_t *filter, double frequency, int samplerate, int iterations);
-void iir_notch_init(iir_filter_t *filter, double frequency, int samplerate, int iterations);
+void iir_notch_init(iir_filter_t *filter, double frequency, int samplerate, int iterations, double Q);
 void iir_process(iir_filter_t *filter, sample_t *samples, int length);
 void iir_process_baseband(iir_filter_t *filter, float *baseband, int length);
 
diff --git a/src/test/test_filter.c b/src/test/test_filter.c
index 3011930..ceaa463 100644
--- a/src/test/test_filter.c
+++ b/src/test/test_filter.c
@@ -85,6 +85,25 @@ int main(void)
 			printf("\n");
 	}
 
+	printf("testing notch filter with %d iterations, Q = 4\n", 1);
+
+	iir_notch_init(&filter_high, 2605.0, SAMPLERATE, 1, 4);
+
+	for (i = 0; i < 4001; i += 100) {
+		gen_samples(samples, (double)i);
+		iir_process(&filter_high, samples, SAMPLERATE);
+		level = get_level(samples);
+		printf("%s%4d Hz: %.1f dB", debug_db(level), i, level2db(level));
+		if (i == 2600)
+			printf(" filter frequency (2605 Hz)\n");
+		else if (i == 2800)
+			printf(" about 200 Hz above\n");
+		else if (i == 2400)
+			printf(" about 200 Hz below\n");
+		else
+			printf("\n");
+	}
+
 	printf("testing band-pass filter with %d iterations\n", iter);
 
 	iir_lowpass_init(&filter_low, 2000.0, SAMPLERATE, iter);