%  Script to high-pass filter w for HW1 using Butterworth filter

  load('rf18L1.txt');
  w = rf18L1(:,4);
  ns = length(w); 
  rate = 25;                         % Data rate

  cutoff = 0.05*2/rate;                 % Cutoff frequency 0.05 Hz
  [b, a] = butter(4,cutoff,'high');
  whi = filtfilt(b,a,w);
