We recently gave every book at books.dev its own narrator. The catalogue has 83 books, so nobody was going to cast them one at a time by ear, but we also didn't want a single default voice reading both Huckleberry Finn and The Turn of the Screw.
Here is the approach. It's simple, and the simple parts are the reason it works.
The voice follows the storyteller, not the author
A first-person novel has an obvious answer: the voice should match the person speaking. Pip looks back on his own life in Great Expectations, so a man reads it. The Turn of the Screw is the governess's own account, so a woman reads it.
Third-person books need a rule too. There, the voice follows the character whose eyes we see the story through.
Age matters as well. Huck Finn is a teenager, so a younger voice reads his book, and the same goes for Jim Hawkins in Treasure Island.
Accent comes from the text
Books written in American or Canadian English get a North American voice. The rest get a British one. So Melville and Twain sound American, while Dickens and Austen sound British. Translations follow the English of the translation: Anna Karenina gets a British voice because its English translation is British.
A model reads, a person decides
A language model read the opening of each book and worked out who the narrator is: a man or a woman, young or grown up. That's a task models do well, and it doesn't need the whole book.
Then a person checked all 83 book-voice pairs and corrected them where needed. Eighty-three is a small enough number for one person to review, and a wrong voice is the kind of mistake that a reader hears in the first minute. The check is cheap compared with what it catches.
One voice for the whole book
Headings, verse and captions are read by the same narrator. Switching voices mid-book for a quote or a chapter title sounds clever in a demo and is tiring after an hour. Where an edition already has a recorded narration, the recording plays first, in the same type of voice, and the narrator reads whatever the recording lacks.
You can hear four of them: Alistair in Great Expectations, Briony in Anna Karenina, Adrian in Moby-Dick and Casey in The Turn of the Screw. The full notes are here.
If you've built something similar, I'd like to know how you handled books with several narrators.
