Your generated mfile suppose to look like this
%UNTITLED Returns a discrete-time filter object.
% M-File generated by MATLAB(R) 7.8 and the Signal Processing Toolbox 6.11.
%
% Generated on: 11-Feb-2011 13:01:59
%
% Butterworth Lowpass filter designed using FDESIGN.LOWPASS.
% All frequency values are in Hz.
Fs = 48000; % Sampling Frequency
Fpass = 9600; % Passband Frequency
Fstop = 12000; % Stopband Frequency
Apass = 1; % Passband Ripple (dB)
Astop = 80; % Stopband Attenuation (dB)
match = 'stopband'; % Band to match exactly
% Construct an FDESIGN object and call its BUTTER method.
h = fdesign.lowpass(Fpass, Fstop, Apass, Astop, Fs);
Hd = design(h, 'butter', 'MatchExactly', match);
% [EOF]
Now you should copy those lines into your script:
Fs = 48000; % Sampling Frequency
Fpass = 9600; % Passband Frequency
Fstop = 12000; % Stopband Frequency
Apass = 1; % Passband Ripple (dB)
Astop = 80; % Stopband Attenuation (dB)
match = 'stopband'; % Band to match exactly
h = fdesign.lowpass(Fpass, Fstop, Apass, Astop, Fs);
Hd = design(h, 'butter', 'MatchExactly', match);
Dont be afraid of objects. Filtering is simple now, you can use Hd filter object whenever you need to filter any signal:
Sfiltered=filter( Hd, S);
