How can I split the signal in matlab

I have 25 signals. these signals exist as a double. that is, when I want to plot a signal I have, I write the plot (t1, y1) command. I am sharing the screenshot of this graph of my signal with you. My goal here is to divide the signal in two from the place I marked. The left side of the graph is noise, and the right side of the graph is noise + signal. Since I have 25 different signals, the noise width of each is different. The code that I want to write here is that these 25 signals can be automatically divided into two as noise and noise + signal.

[Walter Roberson]

I see no inherent reason to split at the location you indicated ?? What factors led you to choose there?

[studentmatlaber]

this is a signal from a sensor. The left side of the graph is the ambient noise. On the right, the signal is detected. I will divide the signal from the place I marked and take the energy of the noise (for 25 signals) and look at the histogram.

[Walter Roberson]

I don't see it. To me the ambient noise appears to be approximately +/- 0.05 .

Answer 1

[Image Analyst]

How about

index = find(signal > 0.47, 1, 'first');
noisyLeftSide = signal(1:index);
goodRightSide = signal(index+1 : end);

[studentmatlaber]

Thank you very much I have been looking for this for days. Thank you very much

[Image Analyst]

So, is that the way you want to split it or not? If it is, please "Accept this answer", if it's not, then tell us what criteria you want for splitting the signal.

[studentmatlaber]

We manually set the 0.47 value in this chart, but I have 600 signals. Can it be written into a code that can automatically determine this threshold value?

[Walter Roberson]

No, but we just might be able to estimate the +/- 0.05-ish noise that I propose is the true ambient noise. It is not clear to me that 0.47 is objectively justifiable.