Reducing noise in a signal is provided. A first filter includes a selectively definable passband for filtering a first signal used in determining at least one patient parameter. A characteristic analyzer detects a characteristic of a second signal and generates a variability measurement value using a series of data values within the second signal over a previously occurring window of time. A filter controller coupled to the characteristic analyzer uses the variability measurement value to define a characteristic of the passband for the first filter and selectively tunes the passband of the first filter according to the defined characteristic. Related apparatus, systems, techniques, and articles are also described.