Hi there,
anyone could help me to do the fft on my data, i tried the normal methed, it never work out…
the time step is 0.0001 second.
Thanks a lot in advance!
Regards,
Pengju
MATLAB: Ask help to do the fft on the ‘untreatable’ data
exponential decayfft
Related Solutions
Try this:
D = load('FFT.txt');t = D(:,1);s = D(:,2);Ts = mean(diff(t)); % Sampling Time
Fs = 1/Ts; % Sampling Frequency
Fn = Fs/2; % Nyquist Frequency
L = length(t);FTs = fft(s)/L;Fv = linspace(0, 1, fix(L/2)+1)*Fn; % Frequency Vector
Iv = 1:length(Fv); % Index Vector
[pks,locs] = findpeaks(abs(FTs(Iv))*2, 'MinPeakHeight',1E-3);figure(1)loglog(Fv, abs(FTs(Iv))*2)hold onplot(Fv(locs), pks, '^r')gridtext(Fv(locs)*1.1, pks, sprintf('\\leftarrow Peak = %.5f at %.3E Hz', pks, Fv(locs)), 'HorizontalAlignment','left')I'm going to give a solution that says your 3000 data points represent a timeseries of 6 seconds. The code can be modified if that assumption is incorrect. Just have Fs=3000/elapsed-time-in-seconds
X = dlmread('ECG.csv');% assumed that the 3000 points are 6 seconds of data...?
Fs = 3000/6; % [samples/s] sampling frequency
T = 1/Fs; % [s] sampling period
N = 3000; % [samples] Length of signal
t = (0:N-1)*T; % [s] Time vector
deltaF = Fs/N; % [1/s]) frequency intervalue of discrete signal
figure('color','white','position',[70 100 600 900]); subplot(3,1,1);plot(1e3*t,X)title({'Heartbeat data'})xlabel('t (milliseconds)')ylabel('X(t)')% compute the fast fourier transform
Y = fft(X);% manually shifting the FFT
Y = abs(Y/N);Amp = [Y(ceil(end/2)+1:end)' Y(1) Y(2:ceil(end/2))']';if (mod(N,2) == 0)sampleIndex = -N/2:1:N/2-1; %raw index for FFT plot
elsesampleIndex = -(N-1)/2:1:(N-1)/2; %raw index for FFT plotendsubplot(3,1,2);plot(deltaF*sampleIndex, Amp);hold on;idx = find(Amp > 3.5);idx(sampleIndex(idx) < 0) = [];plot(deltaF*sampleIndex(idx), Amp(idx), '+');for k = 1:length(idx) if (idx(k) > (N-1)/2 && Amp(idx(k))>3.5) h = text(deltaF*sampleIndex(idx(k)), Amp(idx(k))+0.15,... ['f=' num2str(deltaF*sampleIndex(idx(k))) ' Hz']); set(h,'rotation',90) endendxlabel('Frequency [Hz]');ylabel('Amplitude');title(['Heartbeat = ' num2str(deltaF*sampleIndex(idx(1))) ' Hz = ' ... num2str(60.0*(deltaF*sampleIndex(idx(1)))) ' BPM']);xlim([0 max(deltaF*sampleIndex)/4]);subplot(3,1,3);half_f = deltaF*(0:(N/2));plot(fftshift([half_f -fliplr(half_f(2:end+mod(N,2)-1))]), ... abs(fftshift(Y)/N));xlabel('Frequency [Hz]');ylabel('Amplitude');title('Using fftshift');This yields:
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