Some basic musical theory might help give you some ideas. High notes vs low notes. Major vs minor keys. Fast vs slow tempo. Harmonies. All things that could correspond to how magic changes reality. Music gets complex, and that complexity can reflect the different ways that magic manifests.

You also might consider how people are making these frequencies. Possibly there are certain materials required to make the sounds. You could have musical instruments or sound-making devices that have a large range but are difficult to learn, simpler devices that can be played more easily but with fewer efffects or less nuance. Maybe single-sound devices that only generate a single effect, meant for novices, or as a safety measure. Perhaps some effects require multiple people making sounds together, either to add complexity (like an orchestra) or for pure volume (like a marching band).

Some groups might be more technical about their use of magic, only using the minimum complexity required to create an effect, while others may treat it as an art that is meant to be aesthetically beautiful as well as functional.

Lots to play with.