THIS 22.1

Butterworth Filter Implementation

Butterworth Filter Implementation

Two refinements have been incorporated:
    		• Reflection of beginning and end of curves to minimise end-effects of filtering (see the figure below).
    		• The curve is first passed forwards through the filter, then the resulting signal is passed through backwards. This procedure minimises phase change errors. The poles and zeros of the filter are calculated such that the desired cut-off frequency is achieved after two passes.


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