Systems and methods are provided for operating a physiological monitoring system for determining a physiological parameter of a subject. The physiological system may comprise a pulse oximetry sensor for generating a photoplethysmography (PPG) signal and a gain controller for setting a light detection level. The system may also comprise a filter for filtering the PPG signal. The filter may comprise at least one of filter history and filter coefficients. The system may comprise a processor for determining the power level of light sources of the pulse oximetry sensor and the light detection gain level, and calculating a scaling factor based on the determined power level and the light detection gain level. The processor may also be used for scaling one or more of the filter history and filter coefficients based on the scaling factor, and determining at least one physiological parameter based on the filtered PPG signal.
