A Closer Look at Phonon TTS. Launching High-Quality On-Device Speech That Tops the Benchmarks.

Two weeks ago, we opened up Phonon, our small text-to-speech model that runs on your own device. It needs no server and no network, and what you type stays with you.

We've been very happy with the reception so far. So here's the story of the launch: why we built Phonon, what it can do, the demos that came with it, and how it did on Hugging Face's Open TTS Leaderboard.

Why a voice should live on your device

Most voice AI lives in the cloud: every sentence makes a round trip to a server. Phonon runs on your own device instead. Your text stays there and the voice works without a network. We’ve also opened the weights. Phonon 31m is Apache 2.0, so you can use it for free, even in a commercial product. The other models are CC BY-NC, so they’re free for non-commercial projects. If you’re building something commercial with those, pricing is based on your number of users, not how much speech you generate.

Getting a good voice to run on a small device has always been hard. You could make the model small, but then it didn’t sound great. Or you could make it sound great, but then it wouldn’t fit. We addressed both.

We announced Phonon in April and spent the next six months building on it with partners and early users. Their feedback helped us to shape this release. The models got smaller, and we added more languages and support for custom voices through voice cloning and voice design.

Phonon is based on the Pocket TTS lineage and as such uses flow matching to generate the audio which is very different from the modeling techniques used in other TTS systems. This is what allowed us to bring this level of quality to such a small model but it created new challenges while training the models. The training was initially numerically unstable and required several tricks to produce quality results on all five languages.

What we released

Demos and first projects

The Hugging Face team built the Transformers integration, so developers could use Phonon in Transformers from day one.