FFT Problem (Returns random results)

Question

I\'ve got this code, but it keeps returning random frequencies from 0 to about 1050. Please can you help me understand why this is happening.

My data length is 1024, sam

Answer 1

Assuming oSignal is filled with complex numbers in such a way, that real and imaginary parts alternate, it might help to change

for(int y=0;y< 8191;y++)

to

for(int y=0;y< 8191;y+=2)

Edit: I didn't even notice that you're passing only 1024 samples. You must pass as many time-domain samples as there will be frequency-domain samples, in your case 4096.

Edit: One more thing: you're obviously trying to find the base frequency of something. Unless that something is a computer generated tone or a human whistle (both of which are very pure tones), you might be disappointed by the result. The simple method you posted barely works for flute.

Edit: For voice and guitar you're out of luck. I wrote a program some time ago that displays the frequency domain, try it out, you'll see the problem. There are also sources available, if you're interested.

Final edit: You might want to read the Wikipedia article on pitch detection. Concentrate on time-domain approaches.