MATLAB: How to plot the spectrum of two segments from this signal

Question

In the signal attached, how can I get the spectrum for the first segment of the signal (the signal before the major peak) and and the third segment of the signal (the signal after the major peak)? This is the code I have used, but unfortunately the figure comes up blank for some reason.

Answer 1

Try this:

D = load('signals (1).mat');
Signal = D.Signal;                                                                                      % Get ‘Signal’
N = length(Signal);
t = linspace(0, 1, N) * N;                                                                              % Create Time Vector
[pk,loc] = findpeaks(Signal, 'MinPeakHeight',1);                                                        % Determine Indices Of Various Components
[trofs,trlocs] = findpeaks(-Signal);
ltidx = find(trlocs < loc, 1, 'last');
gtidx = find(trlocs > loc, 1, 'first');
Out{1} = {Signal(1:trlocs(ltidx)); Signal(trlocs(ltidx)+1:trlocs(gtidx)-1); Signal(trlocs(gtidx):end)}; % ‘Signal’ Cell Array
Out{2} = {t(1:trlocs(ltidx)); t(trlocs(ltidx)+1:trlocs(gtidx)-1); t(trlocs(gtidx):N)};                  % ‘t’ Cell Array
figure
plot(Out{2}{1}, Out{1}{1}, 'r')
hold on
plot(Out{2}{2}, Out{1}{2}, 'g')
plot(Out{2}{3}, Out{1}{3}, 'b')
hold off
grid
xlim([min(t) max(t)])
figure
subplot(2, 2, 1);
plot(Out{2}{1}, Out{1}{1}, 'r')
grid
subplot(2, 2, 2);
plot(Out{2}{2}, Out{1}{2}, 'g')
grid
subplot(2, 2, 3);
plot(Out{2}{3}, Out{1}{3}, 'b')
grid
FFTN = 2^14;
% Fv = linspace(0, 1, fix(FFTN/2)+1);
for k1 = 1:numel(Out{1})
    Ts = mean(diff(Out{2}{k1}));
    Fs = 1/Ts;
    Fn = Fs/2;
    FTSeg{k1} = fft(Out{1}{k1},FFTN);
    Fv{k1} = linspace(0, 1, fix(numel(FTSeg{k1})/2)+1)*Fn;
    Iv{k1} = 1:numel(Fv{k1});
end
ttlcs = {'Signal Before Peak', 'Peak', 'Signal After Peak'};
figure
for k1 = 1:numel(Out{1})
    subplot(numel(Out{1}), 1, k1)
    plot(Fv{k1}, abs(FTSeg{k1}(Iv{k1})*2))
    xlim([0  0.02])
    title(ttlcs(k1))
end

The Plot —