The fastest kernel was not the qualified speech stack

A practical stack and a quality limit

The fitting setup combined HQ4, SDPA, the INT8 GPU codec, 0.8-second chunks, a 200-character budget and a 256-step cap. The BF16 comparison peaked at about 22.8 GiB, beyond the RTX 3060.

Voice control remained difficult: the instructed-pitch test passed only 1/21 HQ4 attempts against its recorded 195 Hz threshold. A BF16 English seed passed, while three Spanish cases failed. These are narrow control tests, not a general voice ranking.

Why I did not promote the fastest result

A Marlin experiment reached roughly 155 ms per generator step, or 6.46 tokens/s over a 48-token test with two runs. The production Triton path was around 180 ms. Complete waveform and token-tail evidence was lost, leaving the faster experiment unqualified for deployment.

A ConvRot W4A8 layer test showed roughly 1.74× speedup and cosine near 0.997, but ran under contention and did not render complete speech.

The decision

Keep complete output validation attached to performance. The October 8 service state was disabled/failed; this report does not claim that an experimental kernel was running in production.

Evidence and publication boundary

This is an edited account of the recorded experiment. The linked archive is private; the methods, aggregate findings and limits are included above. Reference recordings, raw conversations, authentication material and workstation configuration are excluded.

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