Two tones of frequency f_1 and f_2 are played simultaneously.

Two tones of frequency f_1 and f_2 are played simultaneously. The superposition (sum) of the two tones results in a new tone of frequency of f = 504 Hz with an amplitude that varies with a frequency of 4 Hz. The two frequencies are f_1 = Hz and f_2 = Hz (where f_1 < f_2).