Time to First Audio, Measured Right: How a Benchmark Change Made TTS Faster

Coval’s TTS benchmark revised its time-to-first-audio metric in June 2026 to include leading silence within an audio stream, measuring when a user first hears audible sound rather than merely when streamed audio arrives. This methodology change raised Gradium’s reported median latency from 171.9 ms to 429.6 ms without changes to its model or infrastructure, revealing that its prior output contained a median 225 ms of inaudible audio before speech. In response, Gradium retrained its default model to produce audible output in its first 10 ms frame, reducing its perceived TTFA to about 214 ms. Coval detects onset through an RMS loudness threshold rather than voice activity detection, allowing breaths and other audible initial sounds to count as a response. Because the new method makes earlier results incompatible with current ones, pre-change leaderboard rows are excluded from comparisons, while the benchmark’s open-source runner, datasets, and methodology allow independent reproduction of comparable results. The benchmark emphasizes that perceived latency reflects the full user experience but should be considered alongside separate quality measures such as word error rate and tested against real production scenarios.

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