Method and system for obtaining a first signal for analysis to characterize at least one periodic component thereof

System for obtaining a first signal (42;50a-n;76) for analysis to characterize at least one periodic component thereof, including:

• an interface (8,12) for obtaining at least two second signals (18-20;55-57) representative of intensities of captured electromagnetic radiation, each corresponding to a respective different radiation frequency range,
• the first signal (42;50a-n) being at least derivable from an output signal (31;72) obtainable by applying a transformation (22,26,30;59,63,67,71) to the second signals (18-20;55-57) such that any value of the output signal (31;72) is based on values from each respective second signal (18-20;55-57) at corresponding points in time, wherein the system is arranged to
• obtain 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;72) when the signals corresponding to the second signals (18-20;55-57) are captured and the transformation (22,26,30;59,63,67,71) is applied, by at least one of:
• (i) analyzing at least one of the second signals (18-20;55-57), the output signal (31;72) and the first signal (42;50a-n;76) and using the analysis to select at least one value (54) of at least one parameter corresponding to a respective one of the variables and determining influences of at least components of respective second signals (18-20;55-57) on the output signal (31;72) when signals corresponding to the second signals (18-20;55-57) are captured and the transformation is applied;
• 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.