What filter command is actually doing

When i use filter command

y=filter(filnum, filden, x);

it filters the data in vector x with the filter described by vectors filnum and filden to create the filtered data Y.

I can also say that it convolves the signal x with the filter defined by fulnum and filden

Answer 1

[Wayne King]

Hi, yes filter() is convolution.

filter() actually uses what is called a direct-form II transposed structure to implement the convolution.

Answer 2

[moonman]

Thanks a lot King I sent u one more question in ur email which i think u have not received. This question is not related to matlab directly but i need opinion of an expert on this I want to ask that what is the feasibility of implementation for DTMF tone detection by using FFT instead of bandpass filters

Plz comment on it

Answer 3

[Wayne King]

I think detection by using the DFT is the way to go. I understand the exercise you were working on, but I think most real-world algorithms use the DFT. Look at that demo in the Signal Processing Toolbox that uses the Goertzel algorithm for the DFT at a small set of frequencies.