Nazar Kozak

Software Engineer
Mobile applications, cross-platform SDKs, and developer infrastructure

This page lists publications and public artifacts from independent technical work. Research completed from March through June 2026 was separate from client employment.

Publications

Predicting Upcoming Stuttering Events from Three-Second Audio: Stratified Evaluation Reveals Severity-Selective Precursors, and the Model Deploys Fully On-Device

Nazar Kozak · Preprint (arXiv), 2026 Preprint

A 616K-parameter CNN trained on SEP-28k that predicts whether the next three-second window will contain a disfluency. Stratified evaluation reveals severity-selective predictive signal: block prediction AUC 0.601 [0.554, 0.651] and sound-rep AUC 0.617 [0.567, 0.667] (95% bootstrap CIs exclude chance) while fillers and word-reps stay at chance. Cross-corpus zero-shot transfer to pediatric Children-Who-Stutter cohort at AUC 0.66. Lossless export to CoreML / ONNX / TFLite, 0.25 ms Apple Neural Engine latency on iPhone 17 Pro Max.

On-Device Multi-Type Disfluency Detection with Sub-Millisecond Inference on Apple Silicon

Nazar Kozak · Technical preprint, 2026 Preprint

DisfluoSDK, an on-device framework for real-time speech disfluency detection on iOS. CNN models (617K params, 1.2 MB) achieve sub-millisecond CoreML inference. 5-class evaluation on SEP-28K with episode-grouped cross-validation; cross-platform export fidelity verified across PyTorch and CoreML.

Voice Stress Markers Are Orthogonal to Speech Disfluency Labels: A Large-Scale Analysis on SEP-28K

Nazar Kozak · Submitted to Speech Communication (Elsevier), 2026 Under review

Large-scale analysis (N=14,645) showing voice stress markers are orthogonal to disfluency labels. TOST equivalence testing rejects non-equivalence for all 20 correlations at Bonferroni-adjusted α=0.0025. Predictive baselines under episode-grouped 5-fold CV land at chance (AUC 0.51-0.55, 95% CIs cover 0.5).

Adaptive Baseline Calibration for Voice Stress Assessment in Speech Disfluency Monitoring

Nazar Kozak · engrXiv Preprint, 2026 Preprint

Welford-based adaptive baseline algorithm for per-speaker voice stress calibration. Fixed thresholds overestimate stress (61.4% high-stress); adaptive approach produces symmetric distribution. YIN pitch detection achieves 98.1% F0 rate.

Dynamic Multidex Loading for Cross-Platform SDK Integration: Solving the Android 65K Method Limit in Mobile Ad Mediation

Nazar Kozak · Preprint (Zenodo), 2026 Preprint

A system for runtime DEX loading on Android that addressed the 65K method-reference limit for cross-platform SDK integration. Originally developed at Appodeal.

Research Artifacts

Public model adapters produced as supporting artifacts for the independent Disfluo research project, March–June 2026.

whisper-small-disfluent-smoothed-lora

LoRA adapter for OpenAI Whisper-small · ASR for stuttered / disfluent speech

Smoothed transcription mode — recovers the speaker's intended words and drops disfluencies. WER 20.46% on FluencyBank Adults Who Stutter (vs 26.04% baseline, −21.4% relative). 13.5 MB adapter, applies on top of base Whisper-small.

whisper-small-disfluent-verbatim-lora

LoRA adapter for OpenAI Whisper-small · verbatim ASR (preserves disfluencies)

Verbatim transcription mode — preserves filled pauses (uh, um), exact word repetitions, and partial-word fragments for clinical / research use. WER 20.29% on held-out validation (−22% relative).

Professional Membership

Google Scholar · ORCID: 0009-0001-8858-6098 · GitHub · Hugging Face · nzrkzk@gmail.com