Jamie Foxx (who was already a classically trained pianist) learned to play the cello for the film.
In the scene in which Nathaniel Ayers (Jamie Foxx) and Steve Lopez (Robert Downey, Jr.) attend a rehearsal concert, all the seats are covered with canvas. This was not cinematic imagery. This is actually done in some concert halls during rehearsals to reflect a more accurate sound, as if the seats were being occupied.
Jamie Foxx had his teeth ground down for the role of Ayers. He says, "My teeth are just so big and white, a homeless person would never have them."
The writing of the book and the selling of the film rights have helped pay Ayers' expenses and helped his sister, a mental health professional, set up a foundation for him.
The real Nathaniel Ayers was invited to view the filming of the scenes at Disney Hall in Los Angeles, but opted on the day to set up his cello and music across the street and continue playing, saying "I really got something going here. I think I'm going to stay and play this just a little bit longer." Steve Lopez spoke about this incident in an interview conducted by Dave Davies for National Public Radio's program Fresh Air in April 2008. He added: "I look(ed) across (the street from Disney Hall) and there he is sawing away, as he calls it, and inside this building there are maybe three hundred people, the Los Angeles Philharmonic, the cast, the crew, are shooting a movie about his life, and I said to Producer Gary Foster, 'You know what Gary? We picked the right name for this thing, The Soloist. There he is.'"