I have to confess that this chapter was the most dificult to understand fromi the technical aspects standpoint. Specially because it gets into the phase, frequencies, feedback, time, etc.. But very interesting. Here some lnks that help me to get a good understanding of this.
https://www.youtube.com/watch?v=S18iVRd7Wf4
https://www.youtube.com/watch?v=JaYkSQrI_Ek