Hi, can anyone help me.. how to find transfer function of theta band EEG?

theta band frequency=(4-8 Hz) fs=1000

Answer 1

[Star Strider]

Here you go:

Fs = 1000;                                              % Sampling Frequency (Hz)
Fn = Fs/2;                                              % Nyquist Frequency (Hz)
Wp1 = [4.0  8.0]/Fn;                                    % Passband Frequencies (Normalized)
Ws1 = [3.9  8.1]/Fn;                                    % Stopband Frequencies (Normalized)
Rp = 10;                                                % Passband Ripple (dB)
Rs = 50;                                                % Stopband Ripple (dB)
[n,Ws] = cheb2ord(Wp1,Ws1,Rp,Rs);                       % Filter Order
[z,p,k] = cheby2(n,Rs,Ws);                              % Filter Design
[sosbp1,gbp1] = zp2sos(z,p,k);                          % Convert To Second-Order-Section For Stability

figure(1)
freqz(sosbp1, 2^17, Fs)
set(subplot(2,1,1), 'XLim',[0  15])                     % ‘Zoom’ X-Axis To See Passband
set(subplot(2,1,2), 'XLim',[0  15])                     % ‘Zoom’ X-Axis To See Passband

theta_eeg = filtfilt(sosbp1, gpb1, original_eeg);       % Filter EEG Signal

[alaisya]

i'm sorry i forgot to mention that i use butterworth second order filter. can you design using this filter? thank you for your help.

[Star Strider]

My pleasure.

The filter I designed for you is better than the one you want. You cannot get good separation without significant leakage with a second-order Butterworth filter at such low frequencies. I have done EEG band separation, and I never used a Butterworth filter, much less a low-order Butterworth filter.

You can change the design yourself, by omitting the cheb2ord call and substituting butter for the cheby2 call, with appropriate changes in the arguments. It will not do what you want.

I leave that to you.

[alaisya]

can you give transfer function of theta band that you get in term of input-output relationship when you using chebyshev filter? your help very helpful for me.. thanks again for help me.

[Star Strider]

As always, my pleasure.

My original code produces a very efficient, relatively short, 20-order filter.

You can calculate the numerator and denominator polynomials of the transfer function with my earlier code by simply adding this assignment:

[b, a] = cheby2(n,Rs,Ws);                               % Filter Design

The ‘b’ and ‘a’ outputs are each (1x41) vectors.

If you want to plot the transfer function, that is in the freqz call in figure(1). See the documentation for freqz to see the other options it offers.

[alaisya]

ok.. tq very much.. if i want to cite you for this coding. How?

[Star Strider]

My pleasure.

I appreciate your wanting to cite me. I have sent you a private message through your Community Profile page.

[Lizhao Du]

Thangks a lot, it is useful, and more important, easy to understand. I would like to cite you for this coding, too.

[Star Strider]

A vote for my Answer would be appreciated!

[Lizhao Du]

Of course I have done it.