Gradium open-sourced Phonon, its on-device TTS engine ( https://gradium.ai/phonon ). That matters less because of the model than because of what it signals: on-device speech synthesis is now a dependency you can ship rather than a research demo. And a wave of teams is about to find out that the hard part of edge speech is not the model. It is that audio is the one component in your app with a hard real-time deadline, and nothing else in your background trained you for that.

Two clocks, and only one of them forgives you

A web request can take 900 ms and nobody dies. An audio callback cannot take 21 ms when it had 20. Once playback starts, the DAC consumes samples at a fixed rate forever, and your synthesis loop has to stay ahead of it. Miss by enough and the buffer underruns: you get a click, a pop, or a robotic stutter that users describe as "the app is broken".

Do the arithmetic once and keep it on the wall. At 24 kHz with a 20 ms mixer period, each callback needs 480 samples.…