Push the pitch too high and upper harmonics fold back as aliasing, the digital audio trap that forces every additive engine to cap its partial count.
In the world
Wagon wheels in old film appear to spin backwards: the camera sampled motion too slowly, and the real motion folded into a false, slower one. Digital audio does the same thing to frequencies above its sampling ceiling.
Digital audio samples 44100 times per second. The Nyquist frequency is half that, 22050 Hz, and any partial above it folds back down into the audible range as a false, inharmonic tone. This is aliasing, and it is the hard ceiling on how many harmonics an additive patch can contain.
The widget shows two rows. The top row is where harmonics should be. The bottom row is what you actually hear. As you push the fundamental up, watch the upper harmonics cross the Nyquist line and bounce back as red bars at the wrong frequencies. That is the fold, and it sounds metallic and wrong.
Did you know?
The wagon-wheel illusion in old westerns is aliasing in the visual domain - film samples motion at 24 frames per second, and any spin faster than 12 rotations per second folds into a phantom backward rotation. Your ears are fooled the same way at 22,050 Hz.
Explore
Two wagon wheels spin side by side: REALITY on the left, WHAT YOU HEAR on the right. Use the slider to increase the spin speed. Below the Nyquist limit both wheels agree. Push past it and the sampled wheel turns red and appears to spin backward - that is aliasing. The same math folds audio frequencies above 22050 Hz into false, wrong-sounding tones.
Most adults cannot hear above 15-17 kHz. Children can often hear past 19 kHz. This threshold drops steadily with age - a frequency you can hear today may be inaudible in ten years. Find your ceiling, then hand the headphones to someone near you and compare.