How does filter function works?

Hi,

I used edit filter to see how does it work but I did not find any relative information. I used FIR filter filter(b,1,signal). I need to know how does it work.

Thankss

Answer 1

[Daniel Shub]

See this filter documentation

doc filter

as well as this question: http://www.mathworks.com/matlabcentral/answers/9900-use-filter-constants-to-hard-code-filter

[Jan]

I agree completely. +1

[khatereh]

Thanks for your answer but what is z ? I am designing a FIR filter so I don't have any a (a=1) but what is z?

Thanksss so much

[Jan]

As explained in the documentation, z is the current status of the filter. The input z is the initial condition of the filter, the z in the output is the final condition. If you omit the input z it is set to the zero matrix.

You find the M-code for the filter command in the link Daniel has posted. There your can inspect what z does.

[Daniel Shub]

@khatereh, it depends on what the context is. As Jan mention it could be the filter state. The term z^(-n) can also represent a delay.

[khatereh]

Thanks for your reply. I calculated coefficient b of low pass filter it is a FIR filter so the a is equal to 1. What should be the input value of z? if you look at the code the z gets updated each time and the final out put of the signal is related to that. I am confused. :(

[Daniel Shub]

I am guessing you want to leave it out. The zi/zf input/outputs are most useful for when you are filtering in blocks. I believe that if you leave zi out, MATLAB assumes that the input has been zero for a very long time.