a method and apparatus for reducing cross - talk in an oximeter . the oximeter includes a band pass filter . the amount of cross - talk through the band pass filter is estimated . based on this estimate , the corner frequencies of the band pass filter are adjusted when it is designed to minimize the cross - talk . in one embodiment , a calibration mode is performed when a sensor is attached to the oximeter . in the calibration mode , the signals are measured with first only the red led on and then with only the ir led on . any signal measured in the off channel is assumed to be a result of cross - talk from the other channel . the magnitude of the cross - talk is determined as a percentage , and subsequently the percentage is multiplied by the actual signal and subtracted from the other led signal as cross - talk compensation .