Howard and Grazer chose frequent collaborator James Horner to score the film because they knew of his ability to communicate. Howard said, regarding Horner, "it's like having a conversation with a writer or an actor or another director". A running discussion between the director and the composer was the concept of high-level mathematics being less about numbers and solutions, and more akin to a kaleidoscope, in that the ideas evolve and change. After the first screening of the film, Horner told Howard: "I see changes occurring like fast-moving weather systems". He chose it as another theme to connect to Nash's ever-changing character. Horner chose Welsh singer Charlotte Church to sing the soprano vocals after deciding that he needed a balance between a child and adult singing voice. He wanted a "purity, clarity and brightness of an instrument" but also a vibrato to maintain the humanity of the voice.