diff --git a/Makefile b/Makefile
index d22af13..705ac2c 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 CFLAGS = -ansi -pedantic -Wall -Wextra -O2 -Ofast -D_DEFAULT_SOURCE
-LDFLAGS = -lX11 -lGL -lGLEW -lm -lrt
+LDFLAGS = -lX11 -lGL -lGLEW -lfftw3 -lm -lrt
 
 shadermeh: shadermeh.o window.o shader.o
 
diff --git a/shadermeh.c b/shadermeh.c
index cbeaf2c..f29af1d 100644
--- a/shadermeh.c
+++ b/shadermeh.c
@@ -22,6 +22,9 @@ static GLfloat vertex_buffer[] = {
 
 static GLubyte audio_buffer[AUDIO_SAMPLES * AUDIO_CHANNELS];
 static float audio_sample_data[AUDIO_SAMPLES];
+static fftw_complex fftw_in[AUDIO_SAMPLES];
+static fftw_complex fftw_out[AUDIO_SAMPLES];
+static fftw_plan plan;
 
 static int try_fetch_audio(void)
 {
@@ -48,9 +51,17 @@ static int try_fetch_audio(void)
 		count += ret;
 	}
 
-	for (i = 0; i < (count / sizeof(float)); ++i) {
+	for (i = 0; i < AUDIO_SAMPLES; ++i)
+		fftw_in[i][0] = audio_sample_data[i];
+
+	fftw_execute(plan);
+
+	for (i = 0; i < AUDIO_SAMPLES; ++i) {
+		float x = fftw_out[i][0], y = fftw_out[i][1];
+		float a = sqrt(x * x + y * y);
+
 		audio_buffer[i + AUDIO_SAMPLES] = audio_sample_data[i] * 127.0f	+ 127.0f;
-		audio_buffer[i] = 0.0f;
+		audio_buffer[i] = 127.0f + a * 127.0f;
 	}
 
 	return 0;
@@ -329,6 +340,11 @@ int main(int argc, char **argv)
 	glSamplerParameteri(sampler_sound, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 	glBindSampler(0, sampler_sound);
 
+	if (have_audio) {
+		plan = fftw_plan_dft_1d(AUDIO_SAMPLES, fftw_in, fftw_out,
+					FFTW_FORWARD, FFTW_ESTIMATE);
+	}
+
 	/******************** framebuffer object ********************/
 	if (to_stdout) {
 		glGenFramebuffers(1, &fbo);
@@ -349,10 +365,6 @@ int main(int argc, char **argv)
 	}
 
 	/******************** drawing loop ********************/
-	for (i = 0; i < AUDIO_SAMPLES; ++i) {
-		audio_sample_data[i] = (float)i / (float)AUDIO_SAMPLES;
-	}
-
 	clock_gettime(CLOCK_MONOTONIC_RAW, &start);
 
 	while (to_stdout || window_handle_events()) {
@@ -426,6 +438,10 @@ int main(int argc, char **argv)
 
 	glUseProgram(0);
 	glDeleteProgram(prog);
+
+	if (have_audio) {
+		fftw_destroy_plan(plan);
+	}
 fail_vao:
 	glBindBuffer(GL_ARRAY_BUFFER, 0);
 	glDeleteBuffers(1, &vbo);
diff --git a/shadermeh.h b/shadermeh.h
index 88b0c8a..1782810 100644
--- a/shadermeh.h
+++ b/shadermeh.h
@@ -27,6 +27,9 @@
 #include <poll.h>
 #include <time.h>
 
+#include <fftw3.h>
+#include <math.h>
+
 #define AUDIO_SAMPLES (512)
 #define AUDIO_CHANNELS (2)