Two physically present tones produce an audible third tone inside the ear

Evidence

The nonlinear distortions produced by the ear can be made audible by playing a constant pure tone (here /1 = 1620 Hz) together with a short sine sweep of similar frequencies (here 12 = 1700 Hz to 3000 Hz). Although physically there are only two tones, a third descending tone with the frequency 2/1 - 12 can be clearly heard. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 3352

Categorization

• DEFINE: Demonstrates the ear’s nonlinear distortion product (2f1-f2) as a concrete listening demonstration.