Butterworth Digital Filters
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Butterworth filters are one of the most commonly used digital filters in motion analysis. They are fast and simple to use. Since they are frequency-based, the effect of filtering can be easily understood and predicted. Choosing a cutoff frequency is easier than estimating the error involved in the raw data in the spline methods. This section contains pages related to Butterworth digital filters: low-pass, band-stop, etc.

Low-Pass Filter
z-Transform
System Function
Filter Function & Coefficients

Two common problems encountered in using Butterworth filters are the phase delay problem and the initial condition problem. The following pages deal with these issues:

Initial Conditions & Data Padding
Phase Delay

The low-pass filter can be transformed to other types of filters such as band-stop:

Other Butterworth Filters
 

Young-Hoo Kwon, 1998-