MATLAB: How to find the frequency of this signal

digital signal processingsignal processing

how can i find the frequency and period of this signal? Thank you

Best Answer

The obvious solution is to use the fft (link) function. There is a low-frequency baseline drift and a high-frequency signal in that appear to be spikes (EKG, perhaps).

To find the peaks and the associated frequencies, use the findpeaks function.

See this Answer (link) for an illustration.

Related Solutions

MATLAB: How to Butterworth Filter with Bandpass [10 500] with sampling rate 1000

You have to divide your passband and stopband frequencies by the Nyquist frequency to normalise them:

Fs = 1000;                                          % Sampling Frequency
Fn = Fs/2;                                          % Nyquist Frequency
Wp = [10  495]/Fn;                                  % Norrmalised Passband Frequencies
Ws = [5   499]/Fn;                                  % Normalised Stopband Frequencies
Rp =  1;                                            % Passband Ripple (dB)
Rs = 25;                                            % Stopband Ripple (dB)
[n,Wn] = buttord(Wp, Ws, Rp, Rs);                   % Optimal Filter Order
[b,a] = butter(n, Wn);                              % Calculate Filter Coefficients
[sos,g] = tf2sos(b,a);                              % Convert To Second-Order Sections For Stability
figure(1)
freqz(sos, 4096, Fs)                                % Filter Bode Plot

You cannot have any frequency exactly at zero or exactly at the Nyquist frequency, so I designed your passband to be close enough to them to be stable. In your filter, you can also use a high-pass design with a lower cutoff of 10 Hz, since your upper passband is at the Nyquist frequency. The passband and stopband ripple values are necessary to specify in the design but irrelevant to a Butterworth filter. These are acceptable values for most filter designs (for example Chebyshev) that require them.

You would use the ‘sos’ and ‘g’ variables in your actual filter:

filtered_signal = filtfilt(sos, g, signal);

(This design works well in R2016a and should also work in earlier releases.)

MATLAB: How to save spectrogram of signal as image ? i have given the code.

x=train_data(91,:,1); 
N=1000;
fs=250; 
t=(1:N)/fs; 
Fn=fs/2; 
Wp=[8 30]/Fn; % Passband Frequency (Normalised) 
Ws=[7.8 31]/Fn; %Stopband Frequency (Normalised) 
Rp=1; % Passband Ripple (dB) 
Rs=150; % Stopband Ripple (dB) 
[n,Ws]=cheb2ord(Wp,Ws,Rp,Rs); % Filter Order 
[z,p,k]=cheby2(n,Rs,Ws); % Filter Design 
[sosbp,gbp]=zp2sos(z,p,k); 
%Filter Signal 
filtered_signal=filtfilt(sosbp, gbp,x); 
Z1=filtered_signal; 
figure spectrogram(Z1,128,120,128,fs,'yaxis') 
title('SPECTROGRAM of MOTOR IMAGERY EEG SIGNAL CHANNEL C3');
saveas(gcf,'filename.png'); %Use to display save as image

Best Answer

Related Solutions

MATLAB: How to Butterworth Filter with Bandpass [10 500] with sampling rate 1000

MATLAB: How to save spectrogram of signal as image ? i have given the code.

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