# Start and end point of a signal

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Amit Daud on 1 Feb 2021
Commented: Amit Daud on 1 Feb 2021
Hello Everyone,
I am fairly new to the MATLAB signal processing. I have a signal which I already threshold. Now, I need to find the start and end point of the signal. i.e. sample number where the signal started to get recognised by detector and the sample number where it did not recognise the signal anymore. Can anyone suggest any method to do so. I have attached some screenshots of the plot of signal for better understanding. I have also attached the matlab code but could not attach the .CSV file as it exceeds the 5MB size limit.
Thanks in ADV.
Amit D.
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### Accepted Answer

Timo Dietz on 1 Feb 2021
Not sure whether I understood your question, but if you want to get the indices of an array for which the data meets certain requirements/thresholds, you can use find.
E.g. if you want to have the indices of all values inside an array which exceed 5, you can just write
idx = find(array_name > 5)
min/max of idx gives you the start and the end index.
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Timo Dietz on 1 Feb 2021
Edited: Timo Dietz on 1 Feb 2021
In case you are just interested in the index, you should have what you need. To be a bit more precise:
First index: idx1 = find(y_array_name > threshold, 1, 'first')
% gives you the first index where the y values exceed 'threshold'
Last index: idx2 = find(y_array_name > threshold, 1, 'last')
% gives you the last index where the y values exceed 'threshold'
In case you have a dedicated x array, just use x(idx1) and x(idx2) to get the corresponding x axis values.
Note: This works for one burst of pulses, only. If you have multiple bursts - each with multpile pulses - and you want to find the start/stop of each individual burst, it's getting much more complicated. In this case you need to have further informations about the nature (e.g. frequency, burst length, ...) of the signals.
Amit Daud on 1 Feb 2021
Ahhh... Got it. Thank you so much for assist.

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