While each company calls their system something different — Yamaha calls their system YPAO, or Yamaha Parametric
room Acoustic Optimizer, seen above — the general premise of the systems is that a small microphone is hooked up to the receiver, placed where the listener's head would be during routine use, and then a series of tones and signals are sent over the speakers to
test for things like echo, muddy sound, and other artifacts.