A method of facilitating obtaining a first signal (42；50a-n) for analysis to characterize at least one periodic component thereof, includes obtaining at least two second signals (18-20) representative of intensities of captured electromagnetic radiation, each corresponding to a respective different radiation frequency range. The first signal (42；50a-n) is at least derivable from an output signal (31) obtainable by applying a transformation (22,26,30) to the second signals (18-20；55-57) such that any value of the output signal (31) is based on values from each respective second signal (18-20；55-57) at corresponding points in time. The method further includes obtaining at least one value of at least one variable determining influences of at least components of respective second signals (18-20；55-57) on the output signal (31) when the signals corresponding to the second signals (18-20；55-57) are captured and the transformation (22,26,30) is applied, by at least one of: (i) analyzing at least one of the second signals (18-20；55-57), an output signal (31) obtained by applying the transformation (22,26,30) to the second signals (18-20) and a first signal (42；50a-n) derived from the output signal (31) and using the analysis to select at least one value of at least one parameter (54) corresponding to a respective one of the variables； and (ii) calculating values of at least one time-varying factor corresponding to a respective one of the variables, each factor value based on at least one second signal value, and applying each factor in an operation in at least one of a number of parallel sequences of operations comprising at least one such operation and taking a signal corresponding to a respective one of the second signals (55-57) as input.
