An economical system and method for extracting amplitude and frequency information from a modulated AC signal are provided. In one embodiment, the invention includes a circuitry implementing op amps, a dual diode, a filter, and a comparator to receive and manipulate the modulated AC signal. The dual diode receives and splits the AC signal into two separate paths, including a baseline path and a filtering path. The AC signal passing through the baseline path remains substantially unchanged, and the AC signal passing through the filtering path passes through a low-pass filter. The signal is then sent through a comparator for comparing amplitudes of the AC signal from the two paths, and the comparator output is received by a microprocessor for controlling a display that generates a visual indicia responsive to the comparator output.