Use of filter when using cumtrapz

I have created a perfect sine wave which i am doing various calculations on however when it comes to integrating using cumtrapz I find myself having to use a filter on the data in order to obtain sensible results. I am wondering why do I see drift in my data as I have a near perfect wave? Also I am wondering about he effect of a filter. Does a filter take data that is oscillating around a particular value and center it around zero

[Matt J]

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