Spectral analysis

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Spectral analysis


Spectral analysis


The "Spectral analysis" window is divided into five sections: "Frequency band", "Selection", "Smoothing", "Spectrum H/V" and "Peak frequency".

This window is used to identify the limits of the analysis in the spectral domain and choose some processing options for the H/V spectral ratio.


Frequency band

In this section is presented information about the frequency band to be taken into account in the analysis process. The fields are:


Maximum/minimum frequency

These two values ​​identify the frequency range within which runs the analysis. When entering the data, if confirmed by pressing the "Enter" key on the keyboard, all spectra are immediately reprocessed.


Frequency step

This value indicates the step with which the frequencies are to be considered in the analysis, ie a reduction of the number of frequencies to be taken into consideration. This arises from the fact that the recordings are made with a sampling frequency which in phase of Fourier transform returns a spectrum with a frequency step much more dense than that actually required in the analysis. Setting the value of this field is possible to encode the Fourier transform to a more significant step. When entering the data, if confirmed by pressing the "Enter" key on the keyboard,  all spectra are immediately reprocessed.



In this section can be excluded from the entire process of analysis the detected windows in the previous phase, on the basis of considerations on the spectra therein. This is done by simply placing/removing the check mark from the box of the row associated with the window in the table in this section that is to be included/excluded. For the criteria for use in the choice of exclusion/inclusion of windows in the process of analysis see the description of HVSR technique and Graphics section of this manual.



In this section can be chosen from the drop-down menu the type of smoothing to be made on the spectra and the relative value to the incisiveness of the same.

In the case of smoothing of Konno & Ohmachi is offered the possibility to set an additional parameter of the bandwith coefficient typical for this type of smoothing.

For more details and for specific methods of smoothing see the techniques in Easy HVSR of this manual.

Moreover, thanks to the option called "Tapering", it is possible to dampen the edge effect of the band analyzed by the technique known as "Tapered cosine window" or "Tukey window".


Spectrum H/V

In this section can be chosen from the drop-down menu the way in which the two traces in the horizontal direction of the recording must be summed to obtain a single value. For more details and for specific methods of directional sum see the techniques in Easy HVSR.


Peak frequency

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


General buttons


The button "Update" is used to refresh the contents of the graphics on the right side of the application window in case changes have been made to different options in this window.



Pressing the button "Apply" become effective the changes made so far.


Graphical configuration

When the window "Spectral analysis" is active a configuration of the right side of the application window that shows the following graphics: in the top the graphic of the average spectra; centrally the graphic of the H/V spectral ratio with its confidence interval; in the bottom part two color maps, the one on the left represents the stationarity of the spectra and the one on the right side represents the directionality of the spectra.




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