Easy HVSR > Techniques in Easy HVSR

Filter

Easy HVSR has one filtering method of the windows, which is based essentially on the evaluation of the relationship between averages useful to identify the possible presence of transients that may have disturbed the recording and then should be discarded. Please note that the application of filter to the windows is not necessary for the purposes of the calculation. As would be discouraged, the user can proceed in the analysis even without applying any filter. This is because in some occasions, this filter can be inconvenient, and a more careful observation of the traces by the user can lead to much better results.

The filter assumes that are already identified the windows and works in the following way :

1.	It is considered, from those identified, a window at a time (its temporal dimension in seconds is referred to as LP)

2.	The window considered has corespondents for peach trace: it is considered one trace at a time

3.	It is performed the average of the values taken from the trace in the time interval of the LP window

4.	The considered window is divided in further temporal windows of SP dimensions (in Easy HVSR this value is entered in the field "Control window size" within the "Filter" section in the "Selection" window)

5.	Is then calculated the average of the values taken by the trace in each sub-window of SP dimensions

6.	Are compared the average of all sub-windows with the average of the window of LP dimension performing the ratio

7.	If even one of these ratios is not within the range of acceptability of the window of LP dimension, is discarded on all traces

8.	The operation is repeated for all the detected windows

An option of this technique consists in considering the residual windows: the size of the SP sub-windows only exceptionally will have multiple dimensions of the dimension LP, for which reason when dividing the windows of LP dimensions in more windows of SP dimension will remain at least one of a dimension smaller than SP.

Easy HVSR provides the possibility to include in the filtering process these residual windows by selecting the dedicated option in the "Selection" window. In the same section are also provided the values that identify the range of validity of the above mentioned ratio.

Further consideration: the dimension SP must obviously be less than the value LP, and should be about an order of magnitude less than the same LP.