Google tests new NotebookLM voices and audio formats Brief, Critique, Debate

Google continues to iterate on its NotebookLM Audio Overview options, quietly preparing three new formats: Brief, Critique, and Debate, in addition to the currently available Deep Dive. These features are hidden behind a feature flag but appear to be operational in the production environment, a typical sign that public rollout could follow soon.

Brief

The Brief format is positioned for those who need a rapid summary, offering a single-voice, two-to-three-minute audio segment that distills key points from the sources provided. Unlike Deep Dive, which lets users choose summary length, Brief remains fixed in duration.

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Critique

Critique shifts focus to feedback, with two AI hosts analyzing your content—such as blog posts or articles—offering specific, actionable suggestions. The length is adjustable between a four-minute short and a longer version. Early testing suggests this mode is useful not only for content creators looking for self-reflection but also for anyone seeking a more critical lens on their material.

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Debate

Debate brings a conversational dynamic, as two hosts take different sides on a topic, illustrating contrasting perspectives on the same sources. For instance, users could feed in discussions about AI advancements and hear a nuanced, back-and-forth argument between the hosts, making it valuable for those interested in hearing multiple sides of an issue or for educational purposes.

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This also means that NotebookLM is advancing on another frequently requested front: Support for more voice options. Currently, users have little control over the AI voices in audio overviews, but new tests show that both additional male and female voices are in use for these new formats (check audio tracks 👀). The ability to choose or mix between different hosts would broaden appeal and address a major gap noted by users since launch (while currently, we have no evidence that it is being developed).

All of this signals Google’s ongoing push to make NotebookLM’s AI-powered audio tools more useful for students, writers, and professionals looking for fresh ways to digest and reflect on information. With these hidden updates, NotebookLM further solidifies its position as a flexible workspace for both structured and creative workflows, aligning with Google’s wider product direction to embed more adaptive, AI-driven customization throughout its productivity ecosystem.