That second graph reminds me of Shepard tones [1], known e.g. from the Super Mario 64 staircase, where each component is steadily rising in pitch, yet the tone

That second graph reminds me of Shepard tones [1], known e.g. from the Super Mario 64 staircase, where each component is steadily rising in pitch, yet the tone as a whole stays exactly the same in the long term. [1] https://en.wikipedia.org/wiki/Shepard_tone https://en.wikipedia.org/wiki/Shepard_tone