For each waveform there is also availabe a more detailed view:
For explanation:
The first diagram is the waveform itself in the “time” domain in fully linear view, in the overview each 8th sample used, in the detail view each second (without any interpolation). The red horizontal line is the average value of the waveform and is only displayed if not zero, means that this waveform has some kind of DC content.
The second diagram is the spectrum view computed by Discrete Fourier Transform of multiple copies of that waveform, using only the absolute values (ignoring phase). The gaps between the value lines are technically correct because a waveform can (by definition) only contain integral multiples of its base frequency and nothing in between. The top left red line is again the DC content, the next line is the base frequency, followed by lines for each integral multiple.
The X axis is in linear scale with divider lines at each octave, marked with the number of octaves above the base frequency… and everybody who know how to calculate octaves immediately understands that this must end at octave 9 if there was a cutoff at 512 times the base.
The Y axis is in a square root scale (to amplify lower levels) but with linear divider lines to split this in 8 segments.
In the overview the spectrum diagram ends at 9th octave, in detail view it goes till 10th so one can check if the cutoff filtering was done good enough (and obviously it was).