import ddf.minim.*;
import ddf.minim.analysis.*;

Minim minim;
AudioPlayer song;
FFT fft;
int nFreqBand = 30;

void setup() {
  size(514, 200);
  minim = new Minim(this);
  song = minim.loadFile("song.mp3", 512);
  fft = new FFT(song.bufferSize(), song.sampleRate());
  song.play();
  colorMode(HSB);
  //The 30th band has a center frequency of 2497.8516 Hz
  //println(fft.indexToFreq(nFreqBand-1));
  noStroke();
}

void draw()
{
  fill(0, 30);
  rect(0, 0, width, height);
  // first perform a forward fft on one of song's buffers
  // I'm using the mix buffer
  //  but you can use any one you like
  fft.forward(song.mix);
  for (int i = 0; i < nFreqBand; i++)
  {
    fill(i*255/nFreqBand, 255, 255);
    rect(i*width/nFreqBand, height, width/nFreqBand, height - fft.getBand(i)*10);
  }
}