diff --git a/main.cpp b/main.cpp
index 60e30e0..58a372e 100644
--- a/main.cpp
+++ b/main.cpp
@@ -5,6 +5,7 @@
 #include <atomic>
 #include <mutex>
 #include <vector>
+#include <complex>
 
 #include <GLFW/glfw3.h>
 
@@ -27,18 +28,35 @@ static int waterfall_height = 700;
 static unsigned int waterfall_data[1600*700];
 
 static void dsp_thread() {
-    std::vector<short int> frames(6400);
+    size_t len = 6400;
+    std::vector<short int> frames(len);
+
+    std::vector<float> frames_f(len);
+    pocketfft::shape_t shape{len};
+    pocketfft::stride_t stride(shape.size());
+    size_t tmp=sizeof(float);
+    for (int i=shape.size()-1; i>=0; --i) {
+        stride[i] = tmp;
+        tmp *= shape[i];
+    };
+    pocketfft::shape_t axes;
+    for(size_t i=0; i<shape.size(); ++i)
+        axes.push_back(i);
+    std::vector<std::complex<float>> frames_ft(len);
     while(!terminate_dsp) {
-        int read_count = snd_pcm_readi(pcm, frames.data(), 6400);
+        int read_count = snd_pcm_readi(pcm, frames.data(), len);
         if(read_count < 0) {
             std::cerr << "read from audio interface failed: " << snd_strerror(read_count) << std::endl;
             break;
         }
+        for(size_t i=0;i<len;i++)
+            frames_f[i] = frames[i];
+        pocketfft::r2c(shape, stride, stride, axes, true, frames_f.data(), frames_ft.data(), 1.0f);
         {
             std::lock_guard<std::mutex> guard(waterfall_data_mutex);
-            std::memmove(&waterfall_data[waterfall_width], &waterfall_data[0], 4*waterfall_width*(waterfall_height - 1));
+            std::memmove(&waterfall_data[waterfall_width], &waterfall_data[0], sizeof(int)*waterfall_width*(waterfall_height - 1));
             for(int i=0;i<waterfall_width;i++) {
-                waterfall_data[i] = 0xff000000 | 0x010101*(frames[i*read_count/waterfall_width]/256 + 128);
+                waterfall_data[i] = 0xff000000 | 0x010101*std::min(int(abs(frames_ft[i*len/(4*waterfall_width)])/10000.), 255);
             }
         }
     };