The Time-FFT function calculates change of signal’s frequency components through time. The signal is divided in smaller, equally spaced segments (possibly overlapped), an FFT for each segment is calculated, and all FFT sequences are used to build a 3D graphic. The same calculation method is used for Spectrogram view.








The FFT calculation parameters depend on your current Spectral analysis defaults. You can change the parameters for the calculated Time-FFT at any time by selecting the “Edit/Properties” option from the main menu or “Properties” from the context menu.


By selecting the “3D-Tools/Time-FFT” option from the main menu, you can set Time-FFT parameters, calculate it, and display as a 3D graphic.


Time FFT parameters




FFT segment length in samples: Length of a signal segment for the FFT calculation.


Number of FFT segments: Number of signal segments. This can be calculated from the segment length and offset parameters.


Offset between segments: Distance (in samples) between beginnings of consecutive signal segments. This can be calculated from FFT segment length and the number of FFT segments.


Frequency range: Frequency range you would like to be displayed in the resulting graphic.



Spectrogram


The spectrogram is a special form of Time-FFT analysis. It is calculated in the same way as a standard Time-FFT, but the resulting graphic is displayed from a top-down perspective. In this view, amplitude variations are represented using color coding - similar amplitude values are always shown in the same color.

To generate a spectrogram, select “3D tools > Spectrogram” from the main menu. This opens the same dialog used for Time-FFT analysis, but the output is displayed as a color-coded spectrogram instead of a 3D plot.

In the spectrogram display:

  • The X-axis always represents time and runs from left to right.
  • The Y-axis shows frequency. You can change the orientation of this axis through the Application settings dialog.


Editing Time-FFT/Spectrogram properties


Once you've created a Time-FFT or spectrogram window, you can modify its parameters such as FFT length, number of segments, and more by right-clicking the window and selecting “Time-FFT properties…” from the context menu.

For quicker adjustments, you can also use the keyboard and mouse together:

  • Hold Ctrl and scroll the mouse wheel forward (up):
    Increases time resolution and decreases frequency resolution by a factor of 2.
  • Hold Ctrl and scroll the mouse wheel backward (down):
    Decreases time resolution and increases frequency resolution by a factor of 2.



Predefined Time-FFT/Spectrogram variants


Various predefined combinations of FFT parameters are available directly from the toolbar or from the main menu: