Early cutoff loses content that cannot be recovered
Aliases: early cutoff · clipped utterance · lost tail · hangover
What it is
If the endpoint fires before the user has finished, capture stops and syllables not yet spoken never enter the buffer. What follows is not a recognition error; it is absent from this request. Loss from premature cutoff usually cannot be recovered from the same audio: with no recording, there is no second decode. Filling in the clipped part requires a new turn.
Why it happens
Commit seals the ring buffer. Microphone samples after that seal, if they are not written into this recognition session, never reach the acoustic model: trailing phonemes, subordinate clauses, and afterthought conditions all drop. Language decoding can still turn the received first half into a complete-looking hypothesis, so the interface appears to have “a result,” hiding that the second half was never captured. Deletion errors and truncation loss are easy to conflate: the former is a word the engine missed in audio it had; the latter is a missing stretch of audio. Extra model accuracy cannot restore a stretch that was never stored. Partial results may still be rolling, but once the endpoint is declared later frames are discarded or assigned to the next turn, and this turn’s hypothesis stops growing.
Studying it
Build sentences known to contain mid-clause pauses or trailing addenda, force several thresholds, and align full transcripts against truncated ones. Label whether the loss is in the buffer (no audio) or in decoding (audio present, word absent). Dependent measures include words cut, information units (slots, negations, the second half of an address), and whether people notice the gap. Word error rate alone books a large deletion for a missing stretch and cannot tell endpointing apart from the recognizer.
Where it stops holding
If the user presses stop, truncation is intended and what is “lost” is what they chose not to say. Streaming recognizers that keep a short hangover after declaring the end may recover the last syllable, but not a whole sentence that was never captured or that was treated as a new turn. A dropped network session can look like a lost tail without being a threshold problem. “Unrecoverable” does not mean the interface cannot offer a respeak: respeak is a new turn, not salvage from the old audio.
Applying it
- Keep a short hangover before declaring the end so the last syllable is not cut; do not imagine the hangover can retrieve a whole sentence after capture has stopped.
- Show the full hypothesis immediately after commit, and offer one-tap respeak or append, so people who notice a missing second clause need not start from a wake word.
- Count “words that were never in the buffer” separately from decoder deletions, or endpoint failures will be filed as recognition-rate problems.