how to zero-pad in frequency domain?
MATLAB: How to zero pad in frequency domain
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in the command line and look for symbolic math toolbox. If it's not in the list, then you would have to purchase it
hello Anna
look at my fft function at the end of my code
clc%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% load signal
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% data
data = importdata('SFC5S_nov25_ST_1_1.txt');dt = 1e-6; % 1 micro seconds
signal = data(:,1);samples = length(signal);Fs = 1/dt; % sampling frequency (Hz)
%% decimate (if needed)
% NB : decim = 1 will do nothing (output = input)
decim = 1;if decim>1 signal = decimate(signal,decim); Fs = Fs/decim;end%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% FFT parameters
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%NFFT = 512; %
OVERLAP = 0.95;% spectrogram dB scale
spectrogram_dB_scale = 80; % dB range scale (means , the lowest displayed level is XX dB below the max level)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% options
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% if you are dealing with acoustics, you may wish to have A weighted
% spectrums
% option_w = 0 : linear spectrum (no weighting dB (L) )
% option_w = 1 : A weighted spectrum (dB (A) )
option_w = 0;%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% display 1 : averaged FFT spectrum
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%[freq, sensor_spectrum] = myfft_peak(signal,Fs,NFFT,OVERLAP);% convert to dB scale (ref = 1)
sensor_spectrum_dB = 20*log10(sensor_spectrum);% apply A weigthing if needed
if option_w == 1 pondA_dB = pondA_function(freq); sensor_spectrum_dB = sensor_spectrum_dB+pondA_dB; my_ylabel = ('Amplitude (dB (A))');else my_ylabel = ('Amplitude (dB (L))');endfigure(1),plot(freq,sensor_spectrum_dB,'b');gridtitle(['Averaged FFT Spectrum / Fs = ' num2str(Fs) ' Hz / Delta f = ' num2str(freq(2)-freq(1)) ' Hz ']);xlabel('Frequency (Hz)');ylabel(my_ylabel);%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% display 2 : time / frequency analysis : spectrogram demo
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%[sg,fsg,tsg] = specgram(signal,NFFT,Fs,hanning(NFFT),floor(NFFT*OVERLAP)); % FFT normalisation and conversion amplitude from linear to dB (peak)
sg_dBpeak = 20*log10(abs(sg))+20*log10(2/length(fsg)); % NB : X=fft(x.*hanning(N))*4/N; % hanning only
% apply A weigthing if neededif option_w == 1 pondA_dB = pondA_function(fsg); sg_dBpeak = sg_dBpeak+(pondA_dB*ones(1,size(sg_dBpeak,2))); my_title = ('Spectrogram (dB (A))');else my_title = ('Spectrogram (dB (L))');end% saturation of the dB range :
% saturation_dB = 60; % dB range scale (means , the lowest displayed level is XX dB below the max level)
min_disp_dB = round(max(max(sg_dBpeak))) - spectrogram_dB_scale;sg_dBpeak(sg_dBpeak<min_disp_dB) = min_disp_dB;% plots spectrogram
figure(2);imagesc(tsg,fsg,sg_dBpeak);colormap('jet');axis('xy');colorbar('vert');gridtitle([my_title ' / Fs = ' num2str(Fs) ' Hz / Delta f = ' num2str(fsg(2)-fsg(1)) ' Hz ']);xlabel('Time (s)');ylabel('Frequency (Hz)');function pondA_dB = pondA_function(f) % dB (A) weighting curve
n = ((12200^2*f.^4)./((f.^2+20.6^2).*(f.^2+12200^2).*sqrt(f.^2+107.7^2).*sqrt(f.^2+737.9^2))); r = ((12200^2*1000.^4)./((1000.^2+20.6^2).*(1000.^2+12200^2).*sqrt(1000.^2+107.7^2).*sqrt(1000.^2+737.9^2))) * ones(size(f)); pondA = n./r; pondA_dB = 20*log10(pondA(:));endfunction [freq_vector,fft_spectrum] = myfft_peak(signal, Fs, nfft, Overlap)% FFT peak spectrum of signal (example sinus amplitude 1 = 0 dB after fft).
% Linear averaging
% signal - input signal,
% Fs - Sampling frequency (Hz).
% nfft - FFT window size
% Overlap - buffer overlap % (between 0 and 0.95)
signal = signal(:);samples = length(signal);% fill signal with zeros if its length is lower than nfft
if samples<nfft s_tmp = zeros(nfft,1); s_tmp((1:samples)) = signal; signal = s_tmp; samples = nfft;end% window : hanning
window = hanning(nfft);window = window(:);% compute fft with overlap
offset = fix((1-Overlap)*nfft); spectnum = 1+ fix((samples-nfft)/offset); % Number of windows
% % for info is equivalent to :
% noverlap = Overlap*nfft;
% spectnum = fix((samples-noverlap)/(nfft-noverlap)); % Number of windows
% main loop
fft_spectrum = 0; for i=1:spectnum start = (i-1)*offset; sw = signal((1+start):(start+nfft)).*window; fft_spectrum = fft_spectrum + (abs(fft(sw))*4/nfft); % X=fft(x.*hanning(N))*4/N; % hanning only
end fft_spectrum = fft_spectrum/spectnum; % to do linear averaging scaling
% one sidded fft spectrum % Select first half
if rem(nfft,2) % nfft odd
select = (1:(nfft+1)/2)'; else select = (1:nfft/2+1)'; endfft_spectrum = fft_spectrum(select);freq_vector = (select - 1)*Fs/nfft;end
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