function setup() {
  createCanvas(1024, 400); 
  fill(255, 40, 255);
  noStroke();
  textAlign(CENTER);

  fft = new p5.FFT();

  p = createP(description);
  var p2 = createP('Description: Using logAverages() to produce the average amplitude \
                    of the 11 octave bands.');

  octaveBands = fft.getOctaveBands(1);
  barsNumber = octaveBands.length;
}
Display the average amount of amplitude across a range
of frequencies using the p5.FFT class and its methods analyze()
and logAverages().

This example divides the frequency spectrum into the first 11 octave bands.
https://courses.physics.illinois.edu/phys193/labs/octave_bands.pdf