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Term

Keyword Glossary (STT)

A keyword glossary for Speech-to-Text is a short, curated list of project-specific terms, brand and product names handed to an STT model as a context hint before transcription — typically through Whisper's `initial_prompt`.

Keyword glossary — explained in more detail

Standard STT models such as Whisper are trained on general web audio and know nothing about domain-specific vocabulary. A keyword glossary is the simplest countermeasure: a list of the ten to twenty most frequent proper names, tools, model and brand names that appear in your workflow. The list is passed to the model per call as a hint (Whisper: initial_prompt). The glossary does not change the model weights — it biases decoding towards known token sequences, so “DEVI Runner” gets recognised consistently instead of ending up as “Debbie Runner”. The leverage is high, the effort minimal: no training, no GPU, no infrastructure.

Example / Practical context

The most effective way to build a keyword glossary is data-driven: collect STT sessions, log every transcription error (e.g. by scoring each session into a CSV with an AI rater), and after ~90 sessions distil the most frequent errors into a list. Whisper-small tolerates roughly 15 terms before general recognition degrades; Whisper-medium leans toward 20–25. Example glossary from a coding workflow: DEVI Runner, boostN, Sonnet, Haiku, Heartbeat, foot pedal, transcription, Claude, CLI, JWT, commit, branch, node, worktree.

Custom vocabulary in commercial APIs (Deepgram, AssemblyAI) is conceptually the same — a project-specific term list, often with boost weights — but cast into the respective API rather than passed as a generic prompt. Fine-tuning the STT model on domain data is the next level: more precise, but more expensive and requiring a training pipeline. A post-processing dictionary corrects Whisper output after the fact (regex- or LLM-based) and addresses different error classes — such as word splits and hallucinations that a hint cannot fix.

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