Abstract: An audio apparatus includes a signal generating circuit for generating a first electrical audio frequency signal corresponding to audio information received from a source, such as a phonograph turntable, tape recorder or FM/AM tuner. A loudspeaker generates an acoustic signal in response to the first audio frequency signal, and a microphone pick-up receives the acoustic signal for generating a corresponding second electrical audio frequency signal. A filter network then separates the first and second audio frequency signals into respective low, mid and high-frequency ranges, and three comparator circuits compare the first and second audio frequency signals in each frequency range and produce a respective error signal in each frequency range.