1. A signal processor which determines an output value for a set of input values, the signal processor comprising: a buffer which stores a window of input values from a signal representative of one or more signals attenuated after emission into tissue at a measurement site; a signal confidence indicator; a memory storing an estimator; and a processor which receives the signal confidence indicator and which accesses the buffer to receive the input values, wherein the processor is configured to execute the estimator using the input values to reduce the input values to a plurality of estimates, and is configured to determine an output value for the window of input values from the plurality of estimates based on a selected time associated with the signal confidence indicator.