Hi all,
I am trying to extract lower alpha (8-10Hz) and upper alpha (10-13Hz) frequency from EEG signal. I have already extracted Alpha, Beta , Gamma and theta bands using Wavelet decomposition in MATLAB, but now I want to use wavelet decomposition to extract lower alpha and upper alpha. Can any body help me out?
Note: for wavelet decomposition I am using the following code to extract details coefficients;
fs=128; %THIS IS MY SAMPLING FREQUENCY
%data is my eeg signal
wavelet = 'db2'; %wavelet function
scale = 5; %No. of wavelet level
[C,L] = wavedec(data, scale, wavelet);
%%%% Calculation the Details Vectors
D1 = wrcoef('d',C,L,wavelet,1); %NOISY
D2 = wrcoef('d',C,L,wavelet,2); %GAMMA
D3 = wrcoef('d',C,L,wavelet,3); %BETA
D4 = wrcoef('d',C,L,wavelet,4); %ALPHA
D5 = wrcoef('d',C,L,wavelet,5); %THETA
A5 = wrcoef('a',C,L,wavelet,5); %DELTA
thank you
Hi Rab,
with STFT you can look into both, frequency and time information of your signal at the same time. Basically, you apply a FFT (fast fourier transformation) for subsets of your data. Depending on the window size you choose for your data-subsets you can either get a more accurate time information (short time window) or frequency information (larger time window).
This might be useful when you want to identify the intensity of different frequency bands over time in your signal.
FYI: A fft can be performed easily in e.g. Matlab. The command is simply called 'fft'. Let me know if you need further help.
Cheers,
Lukas
Hi, Rab Nawaz
To extract any frequency bands, Wavelet packet algorithms gives you the solution. It is easy for you to implement. Since you already knowing wavelet decomposition and implemented.
with regards
Ravish
Hi Lukas and Ravish,
Thank you so much for your answers.
Lukas, I see the use of STFT is better and someone can get in detailed information about the time and frequency depending upon the window size you choose.
Ravish, yeah you are right, wavelet packet decomposition is a choice to extract the frequency bands. but i was a little confused about the number of decomposition level which is required. This decomposition is in accordance with the sampling frequency of the recording device.
Thank you so much for your information.
BTW, I have extracted different frequency bands (Delta, Theta, Alpha and Beta) from the datsets using digital filtering in MATLAB. I useed elliptic filter for the subject purpose.
Thanks,
Rab Nawaz
Hi, Rab Nawaz,
Some books wrote that theta band is from 8~12hz. If we choose D5 as theta, it i s 8~16hz, right?
My question is that is it ok for the little difference of the bandwidth if we use D5 as theta band?
Thanks,
Sansa
Hi Sansa,
I have not seen any article/book which indicate theta from 8-12Hz. Theta are slow oscillations, 4-7Hz. 8-12Hz is Alpha band.
I am not sure about the sampling rate of your EEG data. If you can get 8-16Hz at D5, so you can further decompose 8-16Hz into 8-12 and 12-16Hz and this way you can extract 8-12Hz (Alpha Band).
Hope this help
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