title: Low Pass Filters and Sampling Frequency
body: <p>I am trying to understand the relationship between low pass filters and sampling frequency. Let's say I have a signal data with sampling frequency (sampling rate 500Hz), and the data represent a signal with a (0-200Hz) frequency. I am trying to get rid off the frequencies over 50Hz ( removing the part from 50-200Hz). In butterworth filter they are talking about sampling frequency.  The frequency bands formulas are based on the sampling frequency, like f_cut/f_sampling. These are all related to sampling frequency although I need remove the extra noise with respect to physical frequency which signal has. How does it work?</p>