Well, music isn’t really our forte so I don’t know how much help we’ll be there.
All jokes aside, one of the best series I’ve seen using music as a form of magic is L.E. Modesitt Jr.’s Spellsong Cycle, starting with The Soprano Sorceress. It’s a fantasy setting that takes place in the land of Erde and follows the adventures of Anna Marshall, a fifty year old singer taken from our world on the day of her daughter’s funeral by means of an unlucky wish. Once in Erde, she becomes a sorceress of great power. Modesitt’s work can be a bit of a slog and these aren’t his best. You might not enjoy them as a reader, but his strength is his world building and as a writer of fantasy you shouldn’t skip him.
There’s a lot of good thinking in the novel. One of them is that it is difficult, if not impossible, for sorcerers to perform together as a duet because the chance of something going wrong is too high. Multiple voices together create more power but it relies on perfect synchronization that is nearly impossible to achieve with complex melodies. However, one warlord does manage to achieve this through hundreds of voices chanting together in an army.
The magic works through a combination of lyrics, visualization, and musical accompaniment usually through a single instrument. A truely skilled Sorcerer cannot just be a singer, they must also be a songwriter and composer. However, some get by memorizing songs and melodies from hearing them. Sorcerers and Sorceress are always singers, but to achieve greater power they need the support of other musicians often in the form of an orchestra. This forces the Sorceress to put a great deal of trust in the skill of her followers because a single mistake could be catastrophic for herself and the other musicians. The result is in setting is that most Sorcerers prefer to work alone without accompaniment. Because their magic takes a great deal of concentration, they also need to be protected in combat from attacking forces.
The sorcerer is also limited by what they know or what they can remember/make up on the spot. The use of magic takes a lot of energy, a Sorceress must eat constantly or they risk burning through their own body.
The setting also used two different kinds of magic: Darksong and Clearsong. The definitions are simplistic, but become complex in application. Darksong affects things that are alive or were once alive, growing plants in a garden for example would be Darksong. However, so would raising the dead and compulsion spells that enforce loyalty. Clearsong affects the non-living or what was never alive, this includes command of the elements, but also building infrastructure like roads or castles.
Both come with their flaws because of it’s easier, Darksong’s are greater. Darksong is easy to cast in the beginning, but over time it becomes more difficult causing double vision and violent headaches. It acts a little like an allergy, the more you do it, the more violent the reaction. Eventually, it will kill the sorcerer.
The Clearsong flaw is: matter cannot be created from thin air, it has to come from somewhere. If you’re going to create roads, you need stone and if that stone is not provided then the magic will find it for you. This means it could come from somewhere safe like a quarry or take it from the ground, shifting the landscape and causing a natural disaster or from a nearby village. It’s also pure destruction, if the sorcerer wants to resolve the situation without bloodshed, they need Darksong or they have to rely on others to do the fighting.
The series covers the effects of how this can affect the socio-political factors of the world. His work also does a good job of combining feminist themes with feudal worlds and handling different ways sexism can assert itself when dealing with a powerful woman.
It’s worth taking a look at for ideas, not just for magic but in how that magic affects the politics, the environment, and the balance of power.