This document discusses how the wave patterns of different musical notes interact to determine whether they sound harmonious together when played. It explains that notes with frequency ratios that result in their waves aligning periodically, such as the ratio of 3:2 between the notes C and G, will sound good together. Chord notes in a C major chord have frequency ratios that produce this alignment. The document also provides a formula to calculate the frequency in Hertz of a note from its MIDI pitch number.