A physiological monitoring system may use photonic signals at one or more wavelengths to determine physiological parameters. The system may receive a photoplethysmograph signal, and generated a difference signal based on the photoplethysmograph signal. The system may specify a segment of the photoplethysmograph signal and a segment of the difference signal. The system may associate each value of the segment of the photoplethysmograph signal to a corresponding value of the segment of the difference signal to generate associated value pairs. The system may compare the associated value pairs to a reference characteristic, and determine a signal quality metric based on the comparison.
