Aliasing

Phantom frequencies

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Different frequencies can produce identical samples.
• Frequencies above half the sample rate fold back to lower ones: aliasing.
• The wagon-wheel effect is aliasing in film.

Steps

1. Disguised waves
2. Backwards wheels
3. Filming a spinning wheel
4. Folding back
5. A frozen rotor
6. Filter first
7. Creeping backwards