Abstract: A tone detector for detecting a multi-tone input signal in the presence of speech and noise, comprising first signal processors that generate output signals indicating the energy level of the input signal with the frequency of one of the component tones being amplified and the frequencies of all other of the component tones being attenuated, a last signal processor that generates an output signal indicating the energy level multiplied by negative one of the input signal with the frequencies of all component tones being attenuated, summing junctions that generate output signals indicating the energy levels of the sum of one of the first signal processor output signals and the last signal processor output signal, and tone validation logic receiving the summing junction output signals that generates a tone detect signal when the summing junction output signals indicate that the component tones satisfy a signaling standard.