"Levelling" out a signal with moving average

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Sandy
Sandy 2012-2-23
I'm doing studies on stress-relaxation with a dynamic displacement. The result I have is a almost sinusoidal signal with a moving average (decreasing due to stress-relaxation).
I'm wondering what is the best way to shift all the waves so that instead of having a moving average, I can have a constant average?
Thanks!
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Tom
Tom 2012-2-23
If it is fairly sinusoidal, you could do an FFT (or several over different 'windows' of data) to determine the time period of one oscillation, and work out an average over this period?
Sandy
Sandy 2012-2-23
Here is a sample of the signal I have:
http://dl.dropbox.com/u/22993792/signal.jpg
I was initially thinking of doing it your way, Tom, but thought maybe there was a quick function in MATLAB that may do it for me quickly! I think if all else fails, manually averaging it will have to do.

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Sean de Wolski
Sean de Wolski 2012-2-23
What about using medfilt1 in the signal processing toolbox?
doc medfilt1
Edit: more
pictures really are worth thousands of words
Use the median filter, medfilt1 to create a new vector and then subtract this from your original.
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Sandy
Sandy 2012-2-23
Thank you all so much! The medfilt1 idea seems to have worked quite well. As suggested, I used medfilt1 to smooth the data as much as possible so it was practically just a single non-linear line and subtracted that from my original result:
http://dl.dropbox.com/u/22993792/medfilt1result.jpg
Unfortunately, it looks like there may be a problem with the initial value as it looks like it starts at 1.4 and immediately falls to 0. Anyhow, I will have a closer look at the problem.
Once again, all the help was very much appreciated!
Honglei Chen
Honglei Chen 2012-2-23
You will have to drop the edge if you use medfilt1 because that is your transient response.

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更多回答（2 个）

Honglei Chen
Honglei Chen 2012-2-23
Maybe you want to try detrend?
doc detrend
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Sandy
Sandy 2012-2-23
Thanks,
I've had a look at the detrend function and it seems that it's for linear trends. I tried using the function on my results and unfortunately it didn't make a difference.
The trend I have decreases non-linearly, kind of like the results here:
http://www.sensorprod.com/research-articles/white-papers/2005_nop/Representative-data-of-Pressure01.jpg
Honglei Chen
Honglei Chen 2012-2-23
Then what I can think of is to do a polyfit on your data and then subtract the resulting fit from your data. But I don't know how good it can work out.

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Gurudatha Pai
Gurudatha Pai 2012-2-23
I would recommend fitting an exponential curve rather than a poly fit. e.g see example 8.10 in Steven M. Kay, "Fundamentals of Statistical Signal Processing: Estimation Theory." pp 257.

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