Voice agents are being pointed at elderly callers, and the assumed risk is that
speech recognition will not hear them. That assumption is wrong, and it is
hiding the failure that is actually happening.
Measured on 2,760 Common Voice clips, matched between age brackets on accent, gender and speaker so the only thing varying is age, and checked against a second 3,189-clip draw that controls for none of it:
word error rate premature cutoff (700 ms)
twenties n=920 6.53% 8.0%
sixties n=920 5.23% -1.31pp * 19.7% +11.6pp *
seventies n=920 4.67% -1.86pp * 16.6% +8.5pp *
* speaker-bootstrapped 95% interval excludes zero
Whisper transcribes older speakers more accurately, not less. And where a
stack endpoints on a fixed silence threshold, those same speakers get talked
over two to two and a half times as often.
That second finding has a caveat that arrived after publication and is worth
reading before quoting the number: a semantic turn model closes most of the
gap. Measured against Pipecat's smart-turn v3 on the same clips, +11.6pp
becomes +5.9pp and stops excluding zero (section 3). The fixed-threshold result
describes a real and common configuration, not every configuration.
python3 bench/run.py reproduces both. No API key, no spend.
Large-v3, wideband, speaker-level 95% intervals:
bracket n spk WER vs twenties
twenties 920 606 6.53% [5.77, 7.40] baseline
sixties 920 240 5.23% [4.65, 5.86] -1.31pp [-2.33, -0.30] excludes zero
seventies 920 116 4.67% [4.12, 5.31] -1.86pp [-2.91, -0.88] excludes zero
Every error type falls with age, so this is not one category masking another:
bracket sub del ins
twenties 5.22% 0.57% 0.74%
sixties 4.19% 0.41% 0.64%
seventies 3.67% 0.41% 0.59%
Deletions in particular do not rise, which is the result you would expect if
quiet or breathy speech were being dropped. It is not being dropped.
It is not a Whisper artifact. The obvious objection is that Whisper's
decoder is a language model, so it might be repairing older speakers' word
choices rather than hearing them better. So the same clips were re-run through
wav2vec2, which is pure CTC: frame-wise, greedy, no decoder and no implicit LM.
bracket Whisper enc-dec wav2vec2 CTC
twenties 6.53% 14.23%
sixties 5.23% -1.31pp 10.30% -3.94pp [-5.52,-2.40]
seventies 4.67% -1.86pp 10.52% -3.72pp [-5.49,-2.08]
Absolute WER is much higher for wav2vec2 (LibriSpeech-only training, no LM), so
only the between-bracket comparison transfers. The effect is larger there and
still excludes zero, which puts it in the acoustics rather than in a decoder.
A voice agent decides the caller has finished by waiting for a fixed stretch of
silence. A pause inside an utterance that exceeds that threshold is heard as
the end of the turn, and the agent starts talking over someone mid-sentence.
WER is blind to this. The words the model did receive can be transcribed perfectly while the caller is cut off every time.
Share of utterances containing an internal pause at least this long:
bracket 400 ms 500 ms 700 ms 1000 ms
twenties 23.3% 17.3% 8.0% 2.0%
sixties 41.5% 33.7% 19.7% 8.7%
seventies 37.3% 28.6% 16.6% 6.2%
All six age-versus-baseline differences exclude zero. At 700 ms the gap is +11.6pp [+7.7, +15.7] for the sixties and +8.5pp [+4.0, +13.6] for the seventies.
The mechanism is in the timing. Older speakers take twice as many internal
pauses and spend twice as long in them:
bracket words/voiced-s pauses/clip pause total
twenties 2.47 1.0 240 ms
sixties 2.20 2.0 480 ms
seventies 2.20 2.0 420 ms
It is not a clean gradient. The sixties are cut off slightly more than the
seventies and their intervals overlap. This reads as an effect that arrives by
60 and plateaus, not a straight line, and it is drawn that way rather than
smoothed.
The eighties, run separately because matching against them would have shrunk every bracket eightfold, are the sharpest case. Only 14 speakers exist, so the intervals are wide — and the effect clears them anyway:
threshold twenties eighties difference [95% CI]
400ms 27.9% 49.2% +21.8% [+6.3%, +36.6%]
500ms 15.6% 40.2% +24.8% [+8.9%, +38.7%]
700ms 4.1% 22.1% +18.1% [+7.9%, +27.2%]
1000ms 0.0% 6.6% +6.5% [+1.7%, +14.5%]
At 700 ms that is a 5.4x gap. Their WER, meanwhile, is 6.24% against 6.01% —
a difference of +0.15pp whose interval comfortably includes zero. The two
findings diverge further with age: recognition stays flat while turn-taking
gets steadily worse.
The result survives a re-draw. Running the whole benchmark again without
accent matching — 3,189 clips, 1,434 speakers, 30 accents instead of 8 —
reproduces the cutoff rates almost exactly:
twenties sixties seventies
matched 8.0% 19.7% 16.6%
unmatched 7.5% 19.3% 16.6%
This is a re-draw from one corpus, not an independent replication: the two samples share 52% of their speakers, though only 18% of their clips. It shows the numbers are not an artifact of one particular draw or of the accent matching. It does not show they generalise beyond Common Voice.
Mark Backman of Daily/Pipecat read an earlier version of this and pointed out that it described the wrong thing: production stacks do not endpoint on a fixed VAD threshold. Pipecat's default is smart-turn, a semantic model that listens to the waveform and grants more time when the turn sounds unfinished.
He is right, so smart-turn v3 was measured on the identical sample. For each
clip, the audio up to an internal pause is fed to the model and it is asked
whether the turn is complete. The speaker demonstrably continues, so
"complete" is a false cutoff.
fixed 700ms threshold smart-turn v3
twenties 8.0% 75.6%
sixties 19.7% +11.6pp * 81.6% +5.9pp [-0.9,+12.9]
seventies 16.6% +8.5pp * 79.7% +4.0pp [-3.6,+11.6]
The gap roughly halves and stops excluding zero. Positive control on whole utterances is flat at 90-91% across brackets.
Two things this does not say. The absolute 76-82% rate is not an error
rate: many internal pauses are legitimate clause boundaries where a turn could
plausibly end, and without human labels on which prefixes sound complete, only
the between-bracket comparison is interpretable. And "includes zero" is not
"no effect" — both point estimates stay positive, and 86 seventies speakers
cannot resolve four points either way.
The practical reading: if you endpoint on a fixed threshold, the age gap is real and large. If you use a semantic turn model, most of it goes away. The published smart-turn benchmark stratifies 31,527 samples across 23 languages but not by speaker age, and its training mix leans on synthetic TTS, which does not pause the way an eighty-year-old does.
Several products now offer daily phone check-ins for older adults that claim to
flag cognitive decline from voice biomarkers. Validating that needs gated
clinical corpora. But a prior question needs no clinical labels and bounds the
claim from below: how much does one healthy person's speech vary between
utterances? A drift detector can only see change that clears the speaker's
own noise.
Measured on 36 speakers with 40+ clips each:
feature within-speaker CV
speech rate ~18%
utterance duration ~23%
number of internal pauses ~76%
total pause time ~96-111%
Converted to the sample needed to resolve a 10% change at 80% power:
feature utterances calls @40/call
speech rate 25 0.6
utterance duration 41 1.0
number of internal pauses 447 11
total pause time 758 19
Pause features — the most frequently cited voice biomarker — vary by about
100% within the same speaker, often within one sitting. Detecting a 10% shift
in total pause time takes roughly three weeks of daily calls per reading, so
a "six-week trend" is two or three noisy measurements. Speech rate and duration
are comfortably usable.
Both directions of error are stated: Common Voice clips from one contributor
are often a single sitting, so real day-to-day variance is larger; and
utterances within one call are correlated, so dividing by 40 overstates the
effective sample. Both push the true requirement up. These are floors.
Common Voice is globally crowdsourced and its younger contributors skew non-native. The twenties bracket is 11.9% India-and-South-Asia English and 46.9% native anglophone; the sixties are 64.4%. Whisper is worse on non-native English, so age and accent are genuinely entangled in this corpus, and an uncontrolled comparison has an obvious alternative explanation.
Brackets are therefore matched on the (accent, gender) pair, holding both
identical by construction: 920 clips per bracket, 8 accents, 392/528
male/female in every bracket.
I expected that to change the answer. It does not. Running the benchmark
both ways, on samples whose accent composition could hardly be more different:
matched unmatched
(8 accents, (30/15/13 accents,
identical mix) differing mix)
twenties 6.53% 6.60%
sixties 5.23% 4.90%
seventies 4.67% 5.11%
The largest disagreement is 0.44pp. Both arms put the sixties and seventies below the twenties, and in both the difference excludes zero. Matching is still the right thing to do — it removes a live alternative explanation and it makes the trend monotonic — but the finding does not rest on it.
This section originally claimed the opposite, on the strength of a 40-clip pilot in which the twenties scored 10.54%. At full sample that figure is 6.60%. The pilot was noise and the story built on it was wrong.
Common Voice's older speakers are volunteers. They chose to sit down at a
computer and record themselves for Mozilla. They are tech-comfortable and
almost certainly healthier of voice than the median 75-year-old on a
post-discharge call. Dysarthria, post-stroke speech and cognitive decline are
absent from this corpus by construction.
So this measures healthy aging, not clinical aging. The right reading of
finding 1 is "age alone does not break recognition", not "recognition is fine
for elderly patients". Those are different claims and only the first is
supported here. A follow-up on a disordered-speech corpus is the honest next
step.
Two narrower limits. Read speech is not conversational speech, and someone
reading a prompt pauses differently than someone answering a question — though
that cuts against finding 2 being an artifact, since read speech should if
anything understate natural pausing. And the eighties bracket has 27 speakers
in the entire split, so it is reported separately rather than folded into the
main comparison, where matching against it would have shrunk every bracket
eightfold. Its intervals are correspondingly wide.
Reported because a reader will ask, not because they changed anything.
- Recording quality.Median SNR 53.2 / 55.7 / 55.9 dB across brackets. No equipment disadvantage, so the WER result is not a microphone result.
- Sentence length.Median 11 words for the twenties and sixties, 10 for the seventies. Short utterances are genuinely harder here — 7.72% WER at 1-7 words against 4.24% at 14+ — so the seventies carry thehardersentences, and the effect survives holding length fixed:
words twenties sixties seventies 1-7 8.75% 8.33% 6.04% 8-10 5.82% 6.37% 4.93% 11-13 6.75% 4.63% 4.50% 14-40 5.66% 3.23% 3.89% - Clip validation.Older clips carry alowercommunity downvote rate (10.1% against 14.2%).
- Speaker prolificacy.One contributor holds 9,792 clips in a single shard; half of all 60+ audio in the split comes from about seven people. Capped at 25 clips per speaker, and all intervals resample speakers rather than clips.
The endpoint finding was nearly an artifact. A relative-energy VAD reported
the eighties being cut off at 42.9%. WebRTC VAD — what production stacks
actually run — disagreed on 36% of those clips and put the median longest pause
at 345 ms where the energy detector said 662 ms. Breathy trailing-off speech
falls under an energy floor, and older speech is exactly what is breathy, so
the cheap detector's error was correlated with the variable under study. WebRTC
is now primary and both are recorded; on the published sample they agree on
80-90% of clips and give the same conclusion.
Accent matching silently undid the gender balance. Taking an accent-wise
subset need not preserve the male/female split, and one run came out 54/46 in
the sixties against 50/50 in the seventies. Matching on the (accent, gender)
pair costs 25 clips per bracket and fixes it exactly.
A fp16 shortcut was verified rather than assumed. The run uses fp16 on MPS
because it is 2.6x faster than fp32 on CPU. A quantised Whisper KV cache is
capable of taking large-v3 from 1.91% WER to 100%, so the shortcut was checked
against a reference: identical 0.0274 WER under fp32/cpu, fp32/mps and fp16/mps.
tests/test_precision.py.
pip install torch transformers huggingface_hub jiwer numpy scipy soundfile webrtcvad-wheels
python3 bench/run.py # primary, accent-matched
python3 bench/analyze.py results/primary.json
python3 -m pytest tests/ -q # 23 tests, one per claim above
The corpus is the CC-0 Common Voice 17 English set via the ungated
fsicoli/common_voice_17_0 mirror. Shard membership is computable from
train.tsv row order, so only the shards the sample needs are downloaded
(~19 GB of 45 GB). The run checkpoints every batch to JSONL and resumes where
it stopped.
METHOD.md has the full design, including why a same-sentence paired design is
impossible in this corpus.
| path | what |
|---|---|
| src/agegap/sample.py | stratified draw: speaker cap, gender balance, accent matching |
| src/agegap/channel.py | G.711 telephony simulation, mu-law and packet loss |
| src/agegap/metrics.py | SNR, speaking rate, and the endpoint-cutoff measure |
| src/agegap/stats.py | pooled WER and speaker-level bootstrap intervals |
| src/agegap/asr.py | Whisper adapter, device and precision selection |
| bench/run.py | the run: chunked, checkpointed, fail-closed |
| bench/analyze.py | the tables above, plus the controlled/uncontrolled contrast |
| bench/replicate_ctc.py | the wav2vec2 architecture control |
| bench/smart_turn_eval.py | Pipecat smart-turn v3 on the same age-matched clips |
| bench/drift_floor.py | within-speaker noise, and what it costs a drift detector |
| tests/ | 26 tests, including one per bug in section 8 |