What do auxiliary notes do in a melody?

Auxiliary notes serve to embellish and enhance a melody by coming between the repeated notes, creating a decorative effect. They are often used to provide interest and movement, helping to break the monotony that can arise when a melody features consecutive notes of the same pitch. By inserting these auxiliary notes, composers create a more fluid and engaging musical line that draws the listener's attention.

The other options, while relevant to melody and harmony, do not accurately describe the primary function of auxiliary notes. For instance, auxiliary notes do not specifically enhance the harmonic structure or form the basis of the melody, as they are more decorative rather than foundational. Additionally, auxiliary notes do not indicate changes in tempo, which relates to the speed of the music rather than melodic embellishment.