Noisy signals may be proved to be useless in the calculation of the shear wave velocity. When no other way of improving signal quality can be found the last means of improvement is the application of a filter in the noisy signal. SPAS 2009 provides the one of the simplest cut-off frequency filters.
Calling the signal filter command
Having selected the noisy signal first, calling the Filter signal command will pop up the dialog shown in Figure 20. The dialog displays filter properties, the original signal, the frequency domain plot of the signal (maximum frequency is limited to 600 Hz) and an overlay plot of the filtered signal (blue color) over the original signal (gray color).
Filter signal dialog
Moving the track bar from right to left will result to limiting the "components" used to build the signal. Any changes made to the cut-off frequency track bar are visible in the frequency plot and the overly report.
Filtered signal
After clicking the OK button SPAS 2009 will prompt a confirmation message in order to commit changes in the selected signal. If you wish to apply this filter on all signals at the same depth, check the Apply to all signals of same depth box.
Confirmation message for applying changes to selected signal