Making sense of GetSpectrumData in Unity 3D. http://forum.unity3d.com/threads/making-sense-of-spectrum-data.90262/#post-589054

Spectrum.cs

using UnityEngine;
using System.Collections;

public class Spectrum : MonoBehaviour
{
	
	public int numOfSamples = 8192; //Min: 64, Max: 8192
	
	public AudioSource aSource;
	
	public float[] freqData;
	public float[] band;
	
	public GameObject[] g;
	
	void Start ()
	{
		freqData = new float[numOfSamples];
		
		int n = freqData.Length;
		
		// checks n is a power of 2 in 2's complement format
		if (!Mathf.IsPowerOfTwo (n)) {
			Debug.LogError ("freqData length " + n + " is not a power of 2!!! Min: 64, Max: 8192.");        
			return;
		}
		
		int k = 0;
		for (int j = 0; j < freqData.Length; j++) {
			n = n / 2;
			if (n <= 0)
				break;
			k++;
		}
		
		band = new float[k + 1];
		g = new GameObject[k + 1];
		
		
		for (int i = 0; i < band.Length; i++) {
			band [i] = 0;
			g [i] = GameObject.CreatePrimitive (PrimitiveType.Sphere);
			g [i].GetComponent<Renderer> ().material.SetColor ("_Color", Color.cyan);
			g [i].transform.position = new Vector3 (i, 0, 0);
			
		}
		
		InvokeRepeating ("check", 0.0f, 1.0f / 15.0f); // update at 15 fps
		
		
	}
	
	private void check ()
	{
		aSource.GetSpectrumData (freqData, 0, FFTWindow.Rectangular);
		
		int k = 0;
		int crossover = 2;
		float speed = 5.0f;

		for (int i = 0; i < freqData.Length; i++) {
			float d = freqData [i];
			float b = band [k];
			
			// find the max as the peak value in that frequency band.
			band [k] = (d > b) ? d : b;
			
			if (i > (crossover - 3)) {
				k++;
				crossover *= 2;   // frequency crossover point for each band.
				Vector3 tmp = new Vector3 (g [k].transform.position.x, band [k] * 32, g [k].transform.position.z);
				g [k].transform.position = Vector3.Lerp (g [k].transform.position, tmp, speed);
				band [k] = 0;
			}
		}
	}
	
	void Update ()
	{
	}
}