How Does a Pedal Point Hold Moving Harmony Together?

A pedal point is a note that is sustained or repeatedly sounded while the harmony in the other voices continues to change. It commonly occurs in the bass, and the name is associated with the long notes playable on an organ's foot pedals. The note may begin as part of a chord, become a non-chord tone as the harmony moves away, and later be absorbed into the harmony again.

Its importance is not merely that one note remains unchanged. The same sound keeps acquiring new relationships. With a tonic pedal, the upper harmonies may travel widely while the ear retains a tonal centre. A dominant pedal often prolongs tension because it continues to demand resolution. Change and stability do not take turns: they reveal one another at the same moment. The more active the upper voices become, the more clearly the fixed point can be heard.

A piano cannot sustain airflow as an organ can, so composers often create continuity through a repeated bass, tremolo or the sustaining pedal. If the player turns it into heavy mechanical striking, the fixed note flattens the harmony above; if it is hidden too much, the music loses structural gravity. A better way to listen is to notice how the “same note” sounds different after every harmonic change. A pedal point is therefore not simple stasis, but a reference that makes change audible.

https://musictheory.pugetsound.edu/mt21c/PedalPoint.html
https://musictheory.pugetsound.edu/mt21c/NonChordTonesIntroduction.html