Contents - Index - Previous - Next

Spectrum Plot

This plot is a 2 dimensional plot of the spectrum.  The horizontal axis shows the frequency in Hertz (Hz).  The vertical axis shows the amplitude of each frequency line.  The amplitude scaling type can be modified using the <Options><Settings>  menu and clicking on the Scaling tab or by clicking the corresponding toolbar button.

The total number of available spectral lines is always equal to the FFT size / 2.  Thus for a 1024 point FFT here will be 512 spectral lines.  The measurement will always start at 0 Hz and extend to 1/2 of the selected Sampling Rate.  

The maximum displayed spectrum is limited on the low and high ends.  The lowest 3 bins contain a DC component and are not displayed; the top 1% of the span often contains alias components and therefore is not displayed.

The zoom buttons on the toolbar allow you to easily adjust the displayed span within the available measurement span; however, the FFT algorithm requires that all frequency lines must be computed regardless of whether or not they are displayed.  

The mouse can be used to directly measure the frequency and amplitude information directly off the plot.  In addition, the <Edit><Copy> menu item will place the current spectral data on the clipboard in tabular format.  This can be directly pasted into any spreadsheet or text file.

Toolbar Controls
Spectrum Plot Options
Spectral Overlays
Cursor Measurements
Right Click Action Menus


See Also:  Scaling  Measurement Accuracy, Performance Issues