How to design a FIR filter with two pass bands

I need to carry out a FIR type multiple bandpass filter of order 100 and want to know how can "firls function" be useful.

Given Data :

-Sampling frequency : 500Hz

- Center frequencies : 20 Hz and 180Hz

- Bandwidth amplitudes : 1 and 5

- Bandwidth : 20 Hz

- Width of the rise and fall regions : 15 Hz

Any documentation or help would be really appreciated.

Answer 1

[Star Strider]

Try this:

Fs = 500;                                                                       % Sampling Frequency
fcomb = [19 19.5 20.5 21 177 177.5 182.5 183];                                  % Frequency Vector
mags = [0 1 0 1 0];                                                             % Magnitude Vector
dev = [0.5 0.1 0.5 0.1 0.5];                                                    % Deviations
[n,Wn,beta,ftype] = kaiserord(fcomb,mags,dev,Fs);
hh = fir1(n,Wn,ftype,kaiser(n+1,beta),'noscale');

figure
freqz(hh, 1, 2^20, Fs)
FrqLim = [0 250];                                                               % Frequency Limits (Optional)
set(subplot(2,1,1), 'XLim',FrqLim)                                              % Optional
set(subplot(2,1,2), 'XLim',FrqLim)                                              % Optional

It should do what you want.

The ‘Optional’ set calls after freqz allow you to ‘zoom in’ on various parts of the spectrum if you want to, in order to see it more clearly and adjust the passbands to your requirements. Here, they are set to present the entire filter spectrum.

[Star Strider]

My pleasure!

That is going to be difficult to do with firls, considering the the lower passband has a bandwidth of only 1 Hz.

In any event, since this is a homework assignment (that was not immediately evident), we give only hints, not actual code.

Write the necessary code to impliment your filter, following the examples on the firls documentation page. We can help you get your code to work, if you have problems with it.

[Abdul Sajeed Mohammed]

Thank you for your response.

[Star Strider]

My pleasure!