What is the relation between loudness and frequency of sound?

From what I know from highschool/early university simple harmonic motions, I believe that there is no necessary link between loudness and frequency. Frequency (the number of times a wave completes an oscillation or cycle in one second) decides the pitch of the sound, while amplitude (the difference in height between the highest point in the sound wave and the lowest point) decides the loudness of the sound.