what is the roll-off factor and cutoff-slope of Butterworth filter?

Discussion in 'MATLAB' started by lucy, Nov 19, 2004.

  1. lucy

    lucy Guest

    Hi all,

    I am doing this in digital domain... I have used the Butterwork lowpass
    filter grabbed from Internet:

    % X and Y matrices with ranges normalised to +/- 0.5
    x = (ones(rows,1) * [1:cols] - (fix(cols/2)+1))/cols;
    y = ([1:rows]' * ones(1,cols) - (fix(rows/2)+1))/rows;

    radius = sqrt(x.^2 + y.^2);

    f = 1 ./ (1.0 + (radius ./ cutoff).^(2*n));

    Then "f" is the frequency domain representation of the filter. n is the
    order of the filter; cutoff is the normolized cutoff frequency between [0,

    Now I want to compute the roll-off factora nd cutoff-slope of this n-order
    Butterworth filter...

    How do I get those? Can anybody give me some pointers?

    Thanks a lot
    lucy, Nov 19, 2004
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