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    %% Design a Butterworth Filter
% Construct a default lowpass filter specification object and design a 
% Butterworth filter. 
d = fdesign.lowpass; 
Lowpass = design(d,'butter','matchexactly','stopband');
fvtool(Lowpass);

%%
% Construct a highpass filter specification object and design a 
% Butterworth filter. 
%  Specify the order to be 8 and 3 dB frequency to be 0.6*pi
%  radians/sample.
d = fdesign.highpass('N,F3dB',8,.6); 
Highpass = design(d,'butter');
fvtool(Highpass)