signal processing - remove unwanted portion from the signal

The signal in the red circle is the portion that I want as shown in figure below. I have many sets of data similar to the signal below that occur at different time interval. I want to remove the unwanted portion and remain the circled portion. Can anyone teach me how to do it?

Thank you so much.

Answer 1

[Star Strider]

Try this using envelope to outline the signals, then with a threshold value to choose the desired region —

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1019175/Signal%20data.csv', 'VariableNamingRule','preserve');
VN = T1.Properties.VariableNames;

figure
plot(T1{:,1}, T1{:,[2 3]})
grid
xlabel(VN{1})
legend(VN{[2 3]}, 'Location','best')
title('Original Signal')

env1 = envelope(T1{:,[2 3]}, 150, 'peak');                              % Calculate 'envelope' Of Both Signals
env1 = max(env1,[],2);                                                  % Take The Maximum Across Rows

figure
plot(T1{:,1}, T1{:,[2 3]})
hold on
plot(T1{:,1}, env1, 'LineWidth',2)
hold off
grid
xlabel(VN{1})
legend(VN{[2 3]}, 'Envelope', 'Location','best')
title('Original Signal With Envelope')

Threshold = 1.5;                                                        % Detection Threshold For 'env1'
Lv = env1 >= Threshold;                                                 % Logical Vector

figure
plot(T1{Lv,1}, T1{Lv,[2 3]})
grid
xlabel(VN{1})
legend(VN{[2 3]}, 'Location','best')
title('Edited Signal')

Change the ‘Threshold’ value to get different results.

.

[Yew Jen Chong]

@Star Strider. Thank you for helping me.

[Star Strider]

As always, my pleasure!

Answer 2

[Image Analyst]

Sure. We could help but you forgot to attach your signal, which hopefully you'll do after reading this:

TUTORIAL: How to ask a question (on Answers) and get a fast answer

In the mean time I'd recomment using movmax and getting a signal where it's less than 10 or so. Then delete those elements. Something like

% Find where signal is in a burst.
maxSignal = movmax(signal, 30);
% Determine which elements have low max value.
quietParts = maxSignal < 10;
% Delete those elements that have low value and are not in a burst.
signal(quietParts) = [];

[Yew Jen Chong]

Thank you @Image Analyst. It works and I can obtained the signal without the unwanted portion. I have attached the files just in case you need it. Currently I just test the code you written in my code to check whether it is working in my signal.

But I still have a question. How do I matached the time with the signal?

Thank you so much for your help.