Speech Recognition
Course overview
Speech recognition, or Automatic Speech Recognition (ASR), converts linguistic content in audio into text. In Agent engineering, a usable result is normally more than a full transcript: it includes segments, timestamps, language, anonymous speaker labels, failure reasons, and audio provenance. Each processing run should join asset_id, source_revision, acquisition and analysis formats, timestamp reference, model/decoder/normalization versions, and segment_id + revision into one evidence chain. Without it, “the same transcript segment” cannot be reproduced, corrected, or deleted.
This course is for learners without audio or deep-learning background. Dynamic material was checked on 2026-07-22. Model commands, supported languages, upload limits, and hardware requirements can change; the course does not treat a repository’s or vendor’s current options as a permanent interface.
Where this fits in the overall path
Speech recognition is in the Extended applications and complex collaboration stage and provides the input channel for a voice Agent. Recognized text can flow into Context Engineering, RAG, and Workflow Automation. Together with Text to Speech, it forms the input/output modules; Real-Time Multimodal Interaction then handles turns, interruptions, tools, and session recovery.
flowchart LR A[Audio asset\nasset_id + source_revision] --> B[Decode and format contract\ntime reference, sample rate, channels] B --> C[Segmentation and recognition\nsegment_id + revision] C --> D[Committed transcript\nmodel, decode, normalization versions] D --> E[Retrieval, summarization, or Agent runtime] E --> F[Tools or high-risk actions] G[Independent identity, policy, and approval] -. gate .-> F
The transcript in this diagram is always untrusted user input. It can support understanding and retrieval, but cannot independently authorize tools, side effects, or identity decisions. Real-time turns, interruption, and action gates are developed separately in Real-Time Multimodal Interaction.
Learning objectives
- Explain the minimal intuition for waveforms, sample rate, channels, frames, and spectra.
- Distinguish the responsibilities and boundaries of conventional acoustic/language modules and end-to-end ASR.
- Design a data contract for VAD, segmentation, timestamps, speakers, and post-processing.
- Distinguish acquisition format, model-analysis format, and subtitle/transcript output format, including time coordinates and revision semantics.
- Calculate WER/CER correctly and inspect quality differences by environment, language, or group slices.
- Compare batch and streaming architectures, and design backpressure, unknown terminal state, privacy, and human review.
- Complete a fully offline synthetic transcript-evaluation project.
Prerequisites
- Python Fundamentals, JSON, and Probability and Statistics are recommended.
- No signal-processing background is required; formulas serve sampling and evaluation intuition only.
Recommended order
- Audio digitization and the ASR pipeline: learn waveforms, sampling, and the output contract.
- Acoustic, language, and end-to-end intuition: understand what different model routes do.
- Data annotation and splitting: establish transcription rules and a leakage-free dataset.
- VAD, segmentation, timestamps, and speakers: turn a continuous meeting into usable segments.
- Batch, streaming, and post-processing: design real-time/offline services and a stable text layer.
- WER, CER, and slice evaluation: measure error under consistent rules.
- Fairness, privacy, deployment, and troubleshooting: cover data boundaries and group differences.
- Project: offline transcript evaluation: run fixture evaluation and interpret the report.
Hands-on entry point
- Main project: Offline transcript evaluation.
- Project assets: evaluation script, synthetic transcript fixture, and contract and CLI regression tests.
- The project does not read or generate audio, download a model, or require a key. It validates synthetic format/time-reference metadata and committed transcripts only, so it cannot prove real-media encoding, audio quality, or recognition quality.
Mastery criteria
- I can explain sample rate, channels, frames, VAD, and speaker diarization.
- I can distinguish recognizing content, identifying who is speaking, and verifying a speaker’s identity.
- I can define partial/final result semantics and revision rules for streaming recognition.
- I can calculate WER/CER by hand and explain how normalization, tokenization, and slicing affect the metric.
- I can design runtime metrics and a controlled diagnostic process that do not record raw audio body content.
- I can run the project, locate timestamp/text problems, and add an anonymous slice.
Connections to other knowledge bases
- Combined audio and image inputs are covered in Multimodal AI.
- For how streaming ASR enters an interruptible dialog state machine and associates with TTS and tool calls, see Real-Time Multimodal Interaction.
- ASR text cleaning, chunking, and retrieval connect to Data Cleaning, Chunking Strategies, and Semantic Search.
- Metric gates and online alerts connect to Evaluation Framework and Runtime Monitoring.
Primary references
The following sources were checked on 2026-07-22:
- OpenAI Whisper repository (one implementation for understanding offline models, dependencies, and format conversion; recheck its current README and model table before installing)
- Robust Speech Recognition via Large-Scale Weak Supervision (the Whisper paper)
- OpenAI Speech to text guide (a current product snapshot: bounded file transcription and real-time transcription use different paths; it does not define this course’s general interface contract)
- NIST OpenASR 2020 Evaluation Plan
- NIST SCTK repository (its README identifies SCTK 2.4.12)
- Python wave standard-library documentation (supports uncompressed PCM WAVE only)
- NIST AI Risk Management Framework
Boundary between facts and recommendations
Whisper, cloud transcription APIs, and real-time sessions are concrete implementations. The asset chain, slicing, logging, and review practices in this course are engineering recommendations that must be validated against your languages, devices, setting, budget, and compliance needs. No model or transcript alone can prove a speaker’s real-world identity or consent.