Linear phase FIR notch filter and IIR notch filter

Question

I want to isolate fundamental frequency with the help of a Linear phase FIR notch filter and a IIR notch filter in Matlab. Can anyone tell me how to do that? I know i have to set the notch frequency at fundamental frequency. But cant understand how to implement on MATLAB.

Answer 1

Things you need to know. The sampling rate. The fundamental frequency which you wish to isolate. FIR filter basic and what order do you want. I would suggest making a band stop filter, with a thin stop band. stop band frequencies fc1 and fc2. Then use the code below.

fc1 = fundamental_freqeuncy1/sampling_rate;
fc2 = fundamental_freqeuncy2/sampling_rate;
N = 10; % number of taps you can change
n = -(N/2):(N/2); % 11 order filter
n = n+(n==0)*eps;
[h] = sin(n*2*pi*fc1)./(n*pi) - sin(n*2*pi*fc2)./(n*pi); 
h(0) =  1 - (2*pi*(fc2-fc1))/pi;
%coefficient for band stop filter... which could be used % as notch filter
[w] = 0.54 + 0.46*cos(2*pi*n/N);  % window for betterment 
d = h.*w;  % better coefficients

Now d are the filter coefficients. and your filter is

freqz(d); % use this command to see frequency response 

After this you need to filter your input using the filter designed by coefficients 'd'. so

y = filter(d,1,X) % X is input, y is filtered output

Answer 2

Here is one IIR notch code you would like to use.

fs = 20000;             %#sampling rate
f0 = 50;                %#notch frequency
fn = fs/2;              %#Nyquist frequency
freqRatio = f0/fn;      %#ratio of notch freq. to Nyquist freq.

notchWidth = 0.1;       %#width of the notch

#%Compute zeros
zeros = [exp( sqrt(-1)*pi*freqRatio ), exp( -sqrt(-1)*pi*freqRatio )];

%Compute poles
poles = (1-notchWidth) * zeros;

figure;
zplane(zeros.', poles.');

b = poly( zeros ); %# Get moving average filter coefficients
a = poly( poles ); %# Get autoregressive filter coefficients

figure;
freqz(b,a,32000,fs) % 32000 are the sample numbers

%filter signal x
y = filter(b,a,x);