# Results

All results below are measured, not estimated. Sample sizes and sources
are stated for every number — see `experiments/EXPERIMENTS.md` for the
full experiment log with hypotheses and decisions.

## Summary table

| Experiment | F1 | Sample | Key finding |
|---|---:|---|---|
| EXP-001 Energy/silence baseline | 0.400 | 90-clip val (Phase 3, 300-clip sample, one training shard) | Weak — fixed silence-duration threshold can't distinguish filler-preceded pauses from real endpoints |
| EXP-002 Acoustic features + Logistic Regression | 0.575 | Same 90-clip val as EXP-001 | Strong improvement over EXP-001; still limited by lack of any lexical/semantic signal |
| EXP-003b Temporal (recent-window) acoustic features | +0.112 F1 delta vs. global-only | Same 90-clip val, feature-set ablation on EXP-002's classifier | Recent-window (100–1000ms tail) features meaningfully help; kept in the default feature set |
| EXP-004 Whisper Tiny frozen encoder + Logistic Regression | 0.693 | 75-clip val (fresh, independent 250-clip sample, same dataset) | Strongest measured approach; specifically reduces filler-associated false-END errors |

**On the EXP-002 vs. EXP-004 comparison**: EXP-002 and EXP-004 used
**different development samples** — both drawn from
`pipecat-ai/smart-turn-data-v3.2-train` using the same general
methodology (stratified sampling across `endpoint_bool`, language,
`dataset` source, `synthetic`), but not the same clips, and not a paired
before/after comparison on identical data. The correct way to describe the
+0.118 F1 difference is: **a directional improvement on independent
samples drawn from the same Smart Turn training distribution** — not a
controlled, paired experiment. This is stated explicitly wherever this
comparison appears in this project's documentation.

## Full metrics

### EXP-001 — Energy/silence baseline
- n=90 (validation split)
- Accuracy: 0.567
- F1: 0.400
- False-END rate: 0.309
- False-CONTINUE rate: 0.629
- Params: 2 (thresholds)

### EXP-002 — Acoustic features + Logistic Regression
- n=90 (same validation split as EXP-001)
- Accuracy: 0.622
- F1: 0.575
- False-END rate: 0.400
- False-CONTINUE rate: 0.343
- Params: 92 (91 features + intercept), ~2,920 bytes
- Inference latency (CPU, Claude sandbox): mean 12.2ms / p95 22.4ms per clip

### EXP-003b — Temporal (recent-window) features ablation
- Same 90-clip val set, same classifier family (Logistic Regression)
- Global-only: accuracy 0.511, F1 0.463, false-END rate 0.509
- Global + recent-window: accuracy 0.622, F1 0.575, false-END rate 0.400
- **Delta F1: +0.112**; delta false-END rate: −0.109; delta false-CONTINUE rate: −0.114
- Both error rates improved simultaneously — not a precision/recall tradeoff in one direction

### EXP-004 — Whisper Tiny frozen encoder + Logistic Regression
- n=75 (validation split from a fresh, independent 250-clip sample: 175 dev / 75 val, seed=42)
- Accuracy: 0.693
- F1: **0.693**
- False-END rate: **0.257**
- False-CONTINUE rate: 0.350
- Encoder params: 8,208,384 (~32.8MB fp32) — matches the confirmed reference Smart Turn architecture's documented ~8M params almost exactly
- Classifier params: 92 (~2,920 bytes)
- Inference latency (Colab T4 GPU): preprocessing ~13.5ms + encoder ~1.7ms + classifier ~0.45ms ≈ **~15.6ms/clip total**

## Filler analysis

Phase 3's error analysis on EXP-002 found that **73% of false-END errors
had filler metadata present** (`midfiller` or `endfiller` = True), versus
50% of false-CONTINUE errors — meaning the acoustic-only model's dominant
failure mode was exactly the case the assessment brief names as hard: a
pause that acoustically resembles an ending but linguistically isn't
(filler-preceded).

Phase 4's EXP-004 evaluation targeted this directly:

| | Acoustic (EXP-002, Phase 3, n=39, `midfiller` only) | Whisper (EXP-004, Phase 4, n=35, `midfiller` OR `endfiller`) |
|---|---|---|
| F1 on filler-flagged clips | 0.529 | **0.722** |

And at the individual-error level: Whisper's false-END errors had a
filler flag present 56% of the time (5/9), down from the acoustic model's
73% — consistent with, though not definitive proof of, Whisper's
representation helping specifically on filler-associated pauses.

**This filler-subset result should be treated as directional, not
conclusive** — sample sizes are modest (35–39 clips), the two
measurements come from different samples, and the slice definitions
differ slightly (Phase 3 used `midfiller` alone, Phase 4 used
`midfiller` OR `endfiller`). The `no_filler_known` slice in Phase 4
(n=7) was too small to draw any conclusion from and is explicitly
excluded from this comparison — see `docs/ERROR_ANALYSIS.md`.

## Latency

**~15.6ms per clip**, measured on a Colab T4 GPU, for the full pipeline
(preprocessing + Whisper encoder forward pass + classifier). This is
**hardware-dependent** and should not be read as a CPU-deployment number
— the acoustic baseline's 12.2ms figure was measured on CPU, so the two
latency numbers are not directly comparable to each other. No CPU-measured
Whisper latency exists yet for this project.

## Limitations

- **Development sample sizes are small.** EXP-001/002/003b: 90-clip
  validation set. EXP-004: 75-clip validation set. Neither approaches
  the scale needed for tight confidence intervals on F1 or slice metrics.
- **EXP-002 and EXP-004 used different samples** — not a paired,
  controlled comparison. See note above.
- **No transcripts exist anywhere in the dataset** (`spoken_text` is
  null for every row, confirmed at the schema level) — no result in this
  project relies on or claims access to what was actually said.
- **No true conversation-level endpoint timestamps exist** — this
  project measures classification accuracy and false-END/false-CONTINUE
  rates, not true wall-clock endpoint latency (time from actual turn
  boundary to system decision). This is stated explicitly everywhere
  latency is discussed.
- **Hindi/Hinglish code-switching cannot be directly verified from
  dataset metadata** — Hindi is present as a language tag (`docs/LANGUAGE_ANALYSIS.md`
  documents real, measured Hindi proportions: 4.2% of the full inspected
  shard), but whether it's naturally code-switched Hindi-English speech or
  monolingual Hindi (plausibly TTS-generated) was never independently
  verified via ASR in this project (EXP-000, proposed in Phase 2, was
  never run). **This project does not claim Hinglish robustness.**
- **GPU-measured Whisper latency differs from CPU deployment latency** —
  a production CPU deployment would likely see meaningfully higher
  encoder latency than the ~1.7ms GPU figure above; this hasn't been
  measured and shouldn't be assumed.
- **No official test-set evaluation has been run.**
  `pipecat-ai/smart-turn-data-v3.2-test` was reserved throughout this
  project and was never used for tuning or evaluation — this is a
  deliberate methodological choice, not an oversight, but it does mean
  no number in this document represents true held-out generalization
  performance in the strictest sense (the "held-out" splits used were
  carved from the training distribution, not the official test set).

## Future work

- Streaming incremental inference (avoid full-buffer recomputation on
  every VAD-triggered call — see `docs/INITIAL_ANALYSIS.md` §5 for the
  design tension this raises with the reference Smart Turn architecture)
- Training/evaluating on a larger sample (the full 270,946-row training
  set, or at least a much larger subset than 250–300 clips)
- A controlled Hinglish challenge set with verified code-switched content
  (via ASR-based verification, EXP-000, never run in this project)
- Final evaluation on the official held-out test set
  (`pipecat-ai/smart-turn-data-v3.2-test`), once the architecture is
  fully locked