how to determine start point?

hi, I have an array of data which gives me a noisy graph that looks like a pulse. I want to determine the start point of the top part of the pulse. I also have several of those arrays and they are not similar to each other at all. I tried taking the top 5% of data, but this doesn't suit all arrays. I also tried using diff, but there is too much noise. can someone help me? thx

[Youssef Khmou]

Ronen, you mean peak detection in 1D signal?

[Ronen]

the start point of upper graph is not the peak of it. I can't use max function or some peak finder function.

[Youssef Khmou]

what type of noise those array contain? try to pass them by low pass filter, use median filter, or use fir1 with chosen cutoff frequency, then take the 5% top .

[Ronen]

it's not exactly noise, just data. I've opened an excel file and used the data (1D array) to creat the graph. filter will corrupt the data. in any case I don't think I can use the the top 5% because the data is varing too much

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/7924-where-can-i-upload-images-and-files-for-use-on-matlab-answers

[Ronen]

ok, I've uploaded it... how do I display it here?

[dpb]

post link