Frequency (FFT)

The frequency plot behaves and looks similar to the time series plot.

It uses FFT to plot the selected time range in the frequency domain. Note that Marple assumes a constant sampling rate, and no missing data points, otherwise the plot may not be entirely accurate.

Toolbar

Change styling of signal

You can change the color or stroke style of the signals in the plot.

Frequency range

You can set the frequency range of the plot. You can also zoom in by clicking and dragging with your right mouse (as in making a selection), just as in the time series plot.

Toggle between units

You can change the unit of the x-axis. Please note that this will mirror the plot.

Additional settings

Behind the settings wheel, there are three additional settings that can be toggled on and off.

Change Scale

Turn this setting on to change the scale of the y-axis to logarithmic. The default setting will show a linear scale.

PSD (Power Spectral Density)

Turn this setting on to show the plot as a power spectral density plot. This can be useful for analyzing random or noisy signals where energy is spread out over many frequencies.

The default display of the FFT plot is of course amplitude.

Remove DC offset

Remove the direct current (DC) component, or the signal's zero-frequency component from the plot.