How to remove offset to the time axis or low frequency trend and asymmetry of a time series data?

I have time series data set. I wish to de-trend the data to make the sine waves symmetric with respect to the time axis. I tried using the detrend command offered in matlab and high pass filtering to data. No of them give me acceptable result. How can I write code to realize this?

Thanks in advance.

Sam Zhu

[Image Analyst]

Maybe you should attach the data. People are probably waiting for that before trying anything.

Answer 1

[Image Analyst]

Do you have the Image Processing Toolbox? If so, use

meanSignal = 0.5 * (imerode(signal, se) + imdilate(signal, se));
newSignal = signal - meanSignal;

Basically it takes the halfway point between the upper envelope and the lower envelope, and subtracts that from the original signal. Pick the se window so that it includes at least one full cycle.