# How can I align deterministic signals?

3 views (last 30 days)
alegio20 on 16 Nov 2023
Commented: alegio20 on 17 Nov 2023
I have some results from a shaking table test that have been carried out.
The input was always the same, however, records where started "by-hand" so they always have different starting times leading to signals that are not aligned. Since I am not an expert in signal processing, I need some help to align them.
I add some example data to this topic to give an idea about the data.

Star Strider on 16 Nov 2023
Probably the easiest way to do this (with these signals) is simply to threshold the beginning of each to get the index, then use that to adjust the start times for each signal to the same offset.
Try this —
files = dir('*.mat');
for k = 1:numel(files)
fn = fieldnames(LD);
L(k) = length(s{k});
Fs = 1;
t{k,:} = linspace(0, L(k)-1, L(k))/Fs;
end
figure
hold on
for k = 1:numel(files)
plot(t{k}, s{k})
% ylim([-1 1])
start(k) = find(s{k} > 0.05,1);
end
hold off
grid
[earliest,eidx] = min(start)
earliest = 8221
eidx = 3
figure
tiledlayout(numel(files),1)
for k = 1:numel(files)
nexttile
plot(t{k}, s{k})
grid
xlim([0.75 1.5]*1E+4)
end
sgtitle('Original Signals')
figure
tiledlayout(numel(files),1)
for k = 1:numel(files)
idxrng = start(k) : numel(s{k});
ta{k} = t{k}(1:numel(idxrng)); % Adjusted Time Vector
sa{k} = s{k}(idxrng); % Adjusted Signal Vector
nexttile
plot(ta{k}, sa{k})
grid
end
.
alegio20 on 16 Nov 2023
Thank you very much!
Star Strider on 16 Nov 2023
As always, my pleasure!

Peter Perkins on 16 Nov 2023
Some of what SS shows might be easier with timetables:
for i = 1:4
signal = load("ew_data"+i+".mat"); signal = signal.ans;
start = find(abs(signal)>0.05,1,'first');
stop = find(abs(signal)>0.05,1,'last');
tt{i} = timetable(signal(start:stop),RowTimes=seconds(1:(stop-start+1))); % dunno what your time units are
end
ttAll = synchronize(tt{:},"union");
ttAll.Properties.VariableNames = "Signal" + (1:4);
stackedplot(ttAll)
alegio20 on 17 Nov 2023
@Star Strider your assumption was correct, and the sampling frequency was the same for every signal: 200 Hz.
alegio20 on 17 Nov 2023
Thanks for all the great suggestion provided! I will indeed try to use synchronize soon!

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