diff --git a/examples/goertzel/main.cpp b/examples/goertzel/main.cpp
index bba105b..b3e3210 100644
--- a/examples/goertzel/main.cpp
+++ b/examples/goertzel/main.cpp
@@ -28,7 +28,7 @@ struct FreqData {
 };
 
 bool g_isCapturing = true;
-int g_nSamplesPerFrame = 1024;
+constexpr int g_nSamplesPerFrame = 1024;
 std::vector<FreqData> g_freqData;
 
 // ref : https://github.com/Harvie/Programs/blob/master/c/goertzel/goertzel.c
@@ -60,11 +60,97 @@ float goertzel_mag(int numSamples, float TARGET_FREQUENCY, int SAMPLING_RATE, fl
     real = (q1 * cosine - q2) / scalingFactor;
     imag = (q1 * sine) / scalingFactor;
 
+    //magnitude = real*real + imag*imag;
     magnitude = sqrtf(real*real + imag*imag);
     //phase = atan(imag/real)
     return magnitude;
 }
 
+// FFT routines taken from https://stackoverflow.com/a/37729648/4039976
+
+int log2(int N) {
+    int k = N, i = 0;
+    while(k) {
+        k >>= 1;
+        i++;
+    }
+    return i - 1;
+}
+
+int reverse(int N, int n) {
+    int j, p = 0;
+    for(j = 1; j <= log2(N); j++) {
+        if(n & (1 << (log2(N) - j)))
+            p |= 1 << (j - 1);
+    }
+    return p;
+}
+
+void ordina(float * f1, int N) {
+    float f2[2*GGWave::kMaxSamplesPerFrame];
+    for (int i = 0; i < N; i++) {
+        int ir = reverse(N, i);
+        f2[2*i + 0] = f1[2*ir + 0];
+        f2[2*i + 1] = f1[2*ir + 1];
+    }
+    for (int j = 0; j < N; j++) {
+        f1[2*j + 0] = f2[2*j + 0];
+        f1[2*j + 1] = f2[2*j + 1];
+    }
+}
+
+void transform(float * f, int N) {
+    ordina(f, N);    //first: reverse order
+    float * W;
+    W = (float *)malloc(N*sizeof(float));
+    W[2*1 + 0] = cos(-2.*M_PI/N);
+    W[2*1 + 1] = sin(-2.*M_PI/N);
+    W[2*0 + 0] = 1;
+    W[2*0 + 1] = 0;
+    for (int i = 2; i < N / 2; i++) {
+        W[2*i + 0] = cos(-2.*i*M_PI/N);
+        W[2*i + 1] = sin(-2.*i*M_PI/N);
+    }
+    int n = 1;
+    int a = N / 2;
+    for(int j = 0; j < log2(N); j++) {
+        for(int i = 0; i < N; i++) {
+            if(!(i & n)) {
+                int wi = (i * a) % (n * a);
+                int fi = i + n;
+                float a = W[2*wi + 0];
+                float b = W[2*wi + 1];
+                float c = f[2*fi + 0];
+                float d = f[2*fi + 1];
+                float temp[2] = { f[2*i + 0], f[2*i + 1] };
+                float Temp[2] = { a*c - b*d, b*c + a*d };
+                f[2*i + 0]  = temp[0] + Temp[0];
+                f[2*i + 1]  = temp[1] + Temp[1];
+                f[2*fi + 0] = temp[0] - Temp[0];
+                f[2*fi + 1] = temp[1] - Temp[1];
+            }
+        }
+        n *= 2;
+        a = a / 2;
+    }
+    free(W);
+}
+
+void FFT(float * f, int N, float d) {
+    transform(f, N);
+    for (int i = 0; i < N; i++) {
+        f[2*i + 0] *= d;
+        f[2*i + 1] *= d;
+    }
+}
+
+void FFT(float * src, float * dst, int N, float d) {
+    for (int i = 0; i < N; ++i) {
+        dst[2*i + 0] = src[i];
+        dst[2*i + 1] = 0.0f;
+    }
+    FFT(dst, N, d);
+}
 }
 
 void GGWave_setDefaultCaptureDeviceName(std::string name) {
@@ -228,11 +314,28 @@ bool GGWave_mainLoop() {
     }
 
     int n = 0;
-    float data[g_nSamplesPerFrame];
+    static float data[g_nSamplesPerFrame];
+    static float out[2*g_nSamplesPerFrame];
     do {
         n = cbWaveformInp(data, sizeof(float)*g_nSamplesPerFrame);
         if (n <= 0) break;
 
+        //FFT(data, out, g_nSamplesPerFrame, 1.0);
+
+        //for (int i = 0; i < g_nSamplesPerFrame; ++i) {
+        //    out[i] = (out[2*i + 0]*out[2*i + 0] + out[2*i + 1]*out[2*i + 1]);
+        //}
+        //for (int i = 1; i < g_nSamplesPerFrame/2; ++i) {
+        //    out[i] += out[g_nSamplesPerFrame - i];
+        //}
+
+        //for (int i = 0; i < (int) g_freqData.size(); ++i) {
+        //    g_freqData[i].mag[g_freqData[i].head] = out[40 + i];
+        //    if (++g_freqData[i].head == (int) g_freqData[i].mag.size()) {
+        //        g_freqData[i].head = 0;
+        //    }
+        //}
+
         for (int i = 0; i < (int) g_freqData.size(); ++i) {
             g_freqData[i].mag[g_freqData[i].head] = goertzel_mag(g_nSamplesPerFrame, g_freqData[i].freq, GGWave::kBaseSampleRate, data);
             if (++g_freqData[i].head == (int) g_freqData[i].mag.size()) {