Spectral analysis

The Tab named Spectral analysis is divided into five sections: "Frequency band"; "Selection"; "Smoothing"; "H/V spectrum"; "Peak frequency".

This tab serves to identify the limits of the analysis in the spectral domain and to choose some processing options of the H/V spectral ratio.

Frequency band

In this section there is the information regarding the frequency band to be taken into consideration in the analysis process. The fields present there are:

Maximum / minimum frequency

These two values identify the frequency interval within which to perform the analysis. When entering the data, if you press the "Enter" key on the keyboard as confirmation, all the spectra are immediately reprocessed.

Frequency step

This value indicates the step with which the frequencies must be considered in the analysis, that is, a reduction of the number of frequencies to be taken into consideration. This arises from the fact that the recordings are carried out with a sampling frequency that, during the Fourier transform, returns a spectrum with a frequency step much denser than the one actually needed in the analysis. By setting the value of this field it is possible to encode the Fourier transform at a more significant step. When entering the data, if you press the "Enter" key on the keyboard as confirmation, all the spectra are immediately reprocessed.

Selection

In this section it is possible to exclude from the entire analysis process some of the windows identified in the previous phase of the analysis, on the basis of considerations about the spectra present therein. This is done simply by adding/removing the check mark from the box of the row associated with the window, in the table of this section, that you want to include/exclude. For the criteria to be used in the choice of excluding/including the windows in the analysis process, see the description of the HVSR technique and the Charts section of this manual.

Smoothing

In this section it is possible to choose, from the drop-down menu present there, the type of smoothing to be performed on the spectra, and the value relating to its incisiveness. In the case of Konno & Ohmachi smoothing, it is possible to set the additional parameter of the band coefficient typical of this type of smoothing.

For further details and for the specifications of the smoothing methods, see the techniques section in Easy HVSR of this manual. Moreover, thanks to the option named Tapering, it is possible to damp the edge effects of the analyzed band through the technique known as "Tapered cosine window" or also "Tukey window".

H/V spectrum

In this section it is possible to choose, from the drop-down menu present there, simply the way in which the two traces in the horizontal direction of the recording must be summed to obtain a single value. For further details and for the specifications of the directional sum methods, see the techniques section in Easy HVSR of this manual.

Peak frequency

This is not really a section, but in its label, when a new H/V spectral ratio is evaluated, the frequency where the peak of the spectral ratio itself is located is simply indicated, with its confidence interval.

General buttons

Update

With the button named Update it is possible to update the content of the charts present on the right of the application window in case changes have been made to the choices made available in this Tab.

Apply

With the button named Apply it is possible to make effective the changes made up to that moment.

Chart configuration

When the Tab named Spectral analysis is active, there is a configuration of the right-hand part of the application window that shows the following charts: at the top, the chart of the average spectra; centrally, the chart of the H/V spectral ratio with its confidence interval; at the bottom, two color maps, of which the one on the left represents the stationarity of the spectra and the one on the right their directionality.

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