MATLAB Answers


Simulating a FIR filter

Asked by Rafael Ludtke on 19 Jun 2019
Latest activity Commented on by Rafael Ludtke on 19 Jun 2019
I've found a lot of examples of how to use the fir1 function to calculate the FIR filter coeficients, but I need to define a input vector of samples, the coeficients and need as return the output vector.
I was able to use the filter function to simulate one sample, but I believe I should combine that with a conv function.
This is the diagram I need to simulate:
Where: x[n] is my input vector.
b[ tap_num ] is the coeficient vector.
y[n] is the output vector.
The "triangle" would be a multiplier between the input and b[ tap_num ];
As example, in a 5 tap filter, using an input like x = [ 0 0 0 1 1 1 1 1 ], and b = [ 1 1 1 1 1 ], the expected would be y = [ 1 2 3 4 5 4 3 2 ]
Whats the simpliest way to define the two input vectors ( x[n] and b[tap_num] ), and get an output vector?
Thank you!


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1 Answer

Answer by David Wilson on 19 Jun 2019
Edited by David Wilson on 19 Jun 2019
 Accepted Answer

Use the filter command. In this case your denominator, (A), coefficients are just 1.
x = [ 0 0 0 1 1 1 1 1 ]' % input
b = [ 1 1 1 1 1 ];
y = filter(b,1,x)
You will note that the solution above handles the initial conditions slightly differently than your proposed solution. However if this is important to you (hint: it shouldn't be unless this is a homework problem), then you need to use filtic to get them set to what you want.

  1 Comment

The difference is because of the order I imagined the input vector would enter the filter, fixing that the output is what I was expecting.
Thank you!

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