Some fixes from arduino forums from user El_Supremo

Contributors.md

@@ -0,0 +1,2 @@
+@jacobrosenthal
+El_Supremo

Goertzel.cpp

@@ -30,7 +30,7 @@ float Q2;
 float sine;
 float cosine;
 
-byte testData[160];
+int testData[160];
 
 Goertzel::Goertzel(float TARGET_FREQUENCY, float BLOCK)
 {
@@ -71,10 +71,10 @@ void Goertzel::ResetGoertzel(void)
 
 
 /* Call this routine for every sample. */
-void Goertzel::ProcessSample(byte sample)
+void Goertzel::ProcessSample(int sample)
 {
   float Q0;
-  Q0 = coeff * Q1 - Q2 + (float) sample;
+  Q0 = coeff * Q1 - Q2 + (float) (sample - 512);
   Q2 = Q1;
   Q1 = Q0;
 }
@@ -94,7 +94,7 @@ void Goertzel::sample(int sensorPin)
 {
   for (int index = 0; index < N; index++)
   {
-    testData[index] = (byte) analogRead(sensorPin);
+    testData[index] = analogRead(sensorPin);
   }
 }
 

Goertzel.h

@@ -12,7 +12,7 @@
   simply massaged it into an Arduino library. I recommend reading his article
   for a full description of whats going on behind the scenes.
 
-  Created by Jacob Rosenthal, June 20, 2012.
+  See Contributors.md and add yourself for pull requests
   Released into the public domain.
 */
 
@@ -36,7 +36,7 @@ class Goertzel
   // library-accessible "private" interface
   private:
 	void GetRealImag(float*,float*);
-	void ProcessSample(byte);
+	void ProcessSample(int);
 	void ResetGoertzel(void);
 
 };

examples/DetectA4/DetectA4.ino

@@ -16,18 +16,22 @@
   simply massaged it into an Arduino library. I recommend reading his article
   for a full description of whats going on behind the scenes.
 
-  Created by Jacob Rosenthal, June 20, 2012.
+  See Contributors.md and add yourself for pull requests
   Released into the public domain.
 */
 #include <Goertzel.h>
 
 int sensorPin = A0;
 int led = 13;
 
-float target_freq=440.0; //must be an integer of 9000/N and be less than
+
+float sampling_freq=8800; 	//on 16mhz, ~8928.57142857143, on 8mhz ~44444 
+							//But we want clean math so rounding to 8800 for a 4440 example
+							// with a bucket the size of 20
+
+float target_freq=440.0; //must be an integer of sampling_freq/N and be less than
                          //sampling_frequency/2 (thanks to Nyquist)
-float n=20.0;
-float sampling_freq=9000.0;
+float n=20.0; 			
 
 Goertzel goertzel = Goertzel(target_freq,n,sampling_freq);