Audible's Controllable TTS Brings Distinct Character Voices to Audiobooks

Audible's technology team is using controllable text-to-speech to give audiobook characters distinct, consistent voices, guided by natural-language descriptions of how dialogue should be delivered. A BookLLM component profiles characters and identifies their dialogue with 97% accuracy in English and 94% in Spanish, while a synthetic-data pipeline trains the model on captioned speech. Dialogue differentiation improved by 3.7 points on a MUSHRA test, with statistically significant listening-experience gains for eight of ten voices across English and Spanish tests.