Application of the Sptool filter

Hi all, As a part of my project, i require a lowpass filter of cut off frequency 50 Hz. This I was able to design using the SPTOOL in matlab.The designed filter was an IIR Butterworth filter.My problem is the fact that I want to use the generated filter in my code.Currently, what I do to use the filter is that I import the signal to be filtered from the matlab workspace to sptool, apply the filter to it and export it back to the workspace.However, I dont want the GUI but want that filter to be applied in my code itself.The m file generated contains objects and such which I am not familiar with.The important thing for me right now is how to use the generated m file of the filter on the array .Is it possible to do such a thing?Thanks in advance

Answer 1

[Vieniava]

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);

[Tejas]

Thanks a lot!! Was able to do it...