MATLAB: Code for signal analysis

electrical analysisImage Processing Toolboxsignal processingSignal Processing Toolbox

I trying to analyse some electric signal data but I'm still a Matlab beginner and need help. I use the code bellow just to plot time and signal, but i want to stract the repetition rate of the signal (Hz/number of pulses per second). I think this is possible if i delimite a threshold for the start. Other problem is: i have two signals together in the same file (one big, other little, a example in the figure). Its possible to calculate the repetition rate for each signal? Follow a example of my data.

Thanks for reading

file = 'filename';
signal=wavread(file); % signal
fs = 48000; % sample rate 
t=[1/fs:1/fs:length(signal)/fs];
plot(t,signal);

Best Answer

I'd take the absolute value of the signal (to flip the bottom part up), then I'd threshold at 0.3 and 0.06 to get the two parts of the signal - the high spikes and the shorter spikes. Then use bwlabel to give an ID number to each spike and use regionprops to compute the centroid of each thresholded spike. Once you know that, you can get the average time between spikes, or whatever other information you might want. Untested code (because you didn't include your data) is below:

bigSpikes = abs(signal) > 0.3;
[labeledSpikes, numberOfSpikes] = bwlabel(bigSpikes);
props = regionprops(labeledSpikes, 'Centroid');
allCentroids = [props.Centroid];
xCentroids = allCentroids(1:2:end)
meanSpacingTall = diff(xCentroids)

Do the same for shortSpikes

shortSpikes = abs(signal) > 0.06;
[labeledSpikes, numberOfSpikes] = bwlabel(shortSpikes);
props = regionprops(labeledSpikes, 'Centroid');
allCentroids = [props.Centroid];
xCentroids = allCentroids(1:2:end)
meanSpacingShort = diff(xCentroids)

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It looks like the signal is going along just fine until suddenly there is a big jump, and then it's fine again. So rather than filter the whole signal, I'd just identify the jump locations, determine the new offset, and subtract that from the signal. Here is the code. It's s fast and simple for loop.

% Initialization steps.
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close all;  % Close all figures (except those of imtool.)
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I think it does a pretty good job, don't you?

MATLAB: How to compute centroidal distances

I assume you mean regionprops(BW, I ,'WeightedCentroid') ? You need an intensity image I, to invoke that option.

Best Answer

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