If two notes are simultaneously played, with frequency that are simple fractions (e.g. 2/1, 3/2 or 5/4), then the composite wave will still be periodic with a short period, and the combination will sound For instance, a note vibrating at 200 Hz and a note vibrating at 300 Hz (a or 3/2 ratio, above 200 Hz) will add together to make a wave that repeats at 100 Hz: every 1/100 of a second, the 300 Hz wave will repeat thrice and the 200 Hz wave will repeat twice. Note that the total wave repeats at 100 Hz, but there is not actually a 100 Hz sinusoidal component present.
Additionally, the two notes will have many of the same partials. For instance, a note with a fundamental frequency of 200 Hz will have harmonics at:
A note with fundamental frequency of 300 Hz will have harmonics at:
The following table shows the ratios between the frequencies of all the notes of the just major scale and the fixed frequency of the first note of the scale.