Getting the Frequency out of a sound

I was wondering how to get the frequency of a wav file.

at the moment i have NumSample = 512 and get the spectrum data of the wav file using FFT every second.

What i want to know is what do i get back from FFT is it 0-511 array of frequency values for that particular bin and if so how can i equate a Hz frequency value from that? HELP

	public struct ANALYSIS_DATA
	{
		public float[] number;
		public double Freak;
		public double Bin;
	}

	void Start () 
	{
		analData = new ANALYSIS_DATA();		
		analData.number = new float[numSamples];
		InvokeRepeating("UpdateAnalysis",0.0f,1.0f);
	}

	public void UpdateAnalysis()
	{
		/* updates every 1 second */
		double max = 0;
		int maxpos = 0;
			
		AudioListener.GetSpectrumData(analData.number, 0,FFTWindow.Rectangular);
			
		for(int i=0; i < numSamples; i++)
		{
			if(Mathf.Abs(analData.number[i])> max)
			{
				max = Mathf.Abs(analData.number[i]);
				maxpos = i;
				
			}
		}
		
		if(maxpos > 0)
			GetAvgBin(maxpos);
	}

	public void GetAvgBin(double num)
	{
		if(num > analData.Bin)
			analData.Bin = num;
	}

Any Help would be great?