Convert a digital filter to transfer function

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I have a coefficients of FIR filter ,found it by 'fir1' function, in general, i want to convert a digital filter to transfer function with apply this formula :

The method :

Design a 48th-order FIR filter passband , with a cutoff frequency w=[0.35 0.65]. Compute the coefficients of the equivalent transfer function.

   % Coefficients of fir filter
   c = fir1(48,[0.35 0.65]);
   %Filter Transfer Function
    [b,a] = tf(c);

The error found:

    Error using tf
    Too many output arguments.

How can i solve this problem? how can i find a transfer function of fir filter with this specifications?

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Answer 1

Stephan 2018-9-6

在 MATLAB Online 中打开

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Hi,

tf has only one output - use:

% Coefficients of fir filter
c = fir1(48,[0.35 0.65]);
%Filter Transfer Function
trans_fun = tf(c);

Best regards

Stephan

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Sandi J 2018-9-6

Thank you for your reply ,but what is the difference between this case and the case in this page https://www.mathworks.com/help/signal/ref/tf.html

Stephan 2018-9-6

编辑：Stephan 2018-9-6

I think it is the type of input. The result of fir1 is a row vector which is input for tf.

The input of the link you provided is a digital filter object.

I think the tf function make a case distinction and changes behavior depending on the input type.

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Convert a digital filter to transfer function

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