Working paper / 2026
Multi-condition Impairment Speech-to-Text Bench
Abstract
Multi-condition Impairment Speech-to-Text Bench (MISTT) measures the speech-to-text models that voice agents depend on. Every model hears the same 2,999 frozen clips of voice-agent calls, doctor–patient consultations and five-language parliamentary speech, plus 400 degraded copies of 100 of them: phone lines, low-bitrate codecs, packet loss, background noise and an intelligible background talker. Streaming models are timed the way an agent waits on them, from the forced end of speech to the final transcript. Accuracy carries bootstrap confidence intervals, and the degraded copies are paired with their clean originals, so robustness is measured on the same words.
v0 · October 2026
Deepgram · Streaming · #30 of 36 streaming by English WER · deepgram-flux-en-stream
English WER
6.58%
95% CI 6.02% to 7.14%
TTFS p50 / p95
95 ms
p95 217 ms
$ / 1k audio min
$7.47
list $0.0065/min
Δ Severe
+15.3 pts
4.13% → 19.39% on 100 clips
| English index | 6.58% | 6.02% – 7.14% |
| pipecat (voice-agent turns) | 3.81% | 3.43% – 4.22% |
| primock57 (doctor–patient) | 9.36% | 8.27% – 10.44% |
| Multilingual (de/fr/es/it pooled) | — | |
| VoxPopuli English | 9.15% | 8.04% – 10.21% |
English substitutions 3.57%, deletions 2.13%, insertions 0.89% · raw (un-normalized) English WER 21.34% · hallucination 0.50% of clips · empty 0.18% · VoxPopuli CER 5.26%
| p50 | p90 | p95 | p99 | max | |
|---|---|---|---|---|---|
| TTFS | 95 ms | 160 ms | 217 ms | 221 ms | 854 ms |
| TTFT | 334 ms | 774 ms | 987 ms | 1.77 s | 5.82 s |
| TTFB | 218 ms | 294 ms | 296 ms | 297 ms | 334 ms |
| Connection setup | 129 ms | 260 ms | 278 ms | 290 ms | 627 ms |
English WER@500 ms 6.58% (final 6.58%) · finals before t0 9.1% · fallback finals 9.3% · partial words later rewritten 5.7%
| Mix | WER | Δ pts (95% CI) | Worse | Rank |
|---|---|---|---|---|
| Clean | 4.13% | — | — | #63 |
| Light | 5.69% | +1.6 (+0.6 to +2.6) | 24/100 | #75 |
| Moderate | 15.43% | +11.3 (+7.7 to +14.9) | 61/100 | #75 |
| Severe | 19.39% | +15.3 (+10.6 to +19.7) | 66/100 | #77 |
| Crosstalk | 24.76% | +20.6 (+16.0 to +25.6) | 82/100 | #67 |
Bleed 4.40% of background-talker words · ranks are out of 81 on the subset.
