FIR filter for ECG signal

Hello everyone, I have a problem that I use FIR filter to eliminate the frequency 60Hz, but it does not work. Could you help me?

b=fir1(6,[0.118 0.122],'stop');
freqz(b,1);
dataIn=load('noisy_ECG.mat');
c=struct2cell(dataIn);
d=cell2mat(c);
dataOut=filter(b,1,d);
e=[0:9999];
plot(e,dataOut)

Answer 1

[Star Strider]

One problem is that your filter is not long enough.

Try this:

b=fir1(64,[0.119 0.121],'stop');
freqz(b,1)

You may also want to refine it to create a more narrow stopband. Without knowing your sampling frequency, I cannot re-design it.

[Duy Nguyen]

thank you, the sampling frequency is 1kHz. So I set cutoff frequency from 59Hz to 61Hz for 60Hz stopband. Could you help me to re-design this filter? thank you very much.

[Star Strider]

My pleasure.

Here you go:

Fs = 1E+3;                                          % Sampling Frequency
Fn = Fs/2;                                          % Nyquist Frequency
b=fir1(48, [59.8 60.2]/Fn, 'stop');
freqz(b, 1, 2^16, Fs)

If you want a much steeper rolloff and much narrower notch, this works:

sb_frq = [58 59 61 62];                                     % Define Passband / Stopband Frequencies
mags = [1 0 1];                                             % Design Lowpass Filter
devs = [0.05  0.01  0.05];                                  % Allowed Deviations
[n,Wn,beta,ftype] = kaiserord(sb_frq,mags,devs,Fs);         % Use Kaiser Window
n = n + rem(n,2);                                           % Define Filter Order
b = fir1(n,Wn,ftype,kaiser(n+1,beta),'scale');              % Design Filter
freqz(b, 1, 2^16, Fs)