How to remove the low frequencey in a data set.

Hi every one, I'm a new user of matlab, anyway I have come up with some displacement from acceleration data by intergrate them twice, but some how I have some low frequencey within the data, I'm wondering how can i remove them. I have attach some pictures with this question, Many Thanks Vincent

[Vincent]

Sorry just want to make my question more clear, can I make the noise displace along the origin? I.e. remove the low frequencey period /cycle

Answer 1

[Chad Greene]

You could use the hipass_butterworth function from this set if you have the signal processing toolbox: http://www.mathworks.com/matlabcentral/fileexchange/38584-butterworth-filters

[Vincent]

Hi Chad, Thanks for the answer, I'm trying to follow the example but I'm not very sure if i have got it right? and I have got a couple of questions. First of all I'm trying to use example 1 as you posted on

>> Filt_S = bandstop_butterworth(detrend_s,[800 1000],Fs,4) Undefined function 'bandstop_butterworth' for input arguments of type 'double'.

this is what I get from matlab, I dont really get why, second question what does it mean by the filter order? i.e. the number 4 in the end.

Finally question for my data set I have got 2000 data and each one has a dt of 0.01 second, as i have attach the data with this comment. my wave frequency is 0.25Hz so when i using the Fs should I use as 0.25 or 0.01 and what is cut off frequencies ?

sorry I have ask so many question as I'm new to matlab.

Kind regard Vincent