# Automatic Speech Recognition

> Automatic speech recognition from classical HMM/WFST pipelines to CTC, RNN-T, Transformer and Conformer models, with WER, domain adaptation and streaming constraints.

- Author: Muhammet Ali Köker
- Language: en
- Canonical: https://alikoker.com.tr/en/automatic-speech-recognition
- Translation: https://alikoker.com.tr/seste-konusma-tanima
- Published: 2022-07-25T01:41:05+03:00
- Modified: 2026-08-31T22:21:00+03:00
- Verified: 2026-08-31T22:07:00+03:00
- Type: article

Automatic speech recognition converts an acoustic signal into words, subwords or characters. The problem combines acoustic representation, temporal alignment, language information and search.

## Classical architectures

Traditional systems combine MFCC-like features, acoustic models, HMM states, pronunciation lexicons and n-gram language models. WFST decoding can integrate these components into a single search graph.

## End-to-end models

In [automatic speech recognition](/en/wiki/automatic-speech-recognition), CTC reduces the need for frame-level alignment. RNN-T is well suited to streaming recognition. Transformer and Conformer architectures model long-range context effectively.

End-to-end modelling does not remove the need for VAD, resampling, channel handling and segmentation. These stages determine the structure of the model input.

## Domain adaptation

Technical terms, names and organisation-specific vocabulary may be weakly represented by general language models. Contextual biasing, rescoring and domain adaptation can improve recognition of such terms.

[Word Error Rate](/en/wiki/word-error-rate) is the standard aggregate metric. Numbers, names and critical terms can also be evaluated separately.

For real-time systems, WER should be considered together with real-time factor, segment latency, timestamp accuracy and result stability.

## Cite This Work

Köker, M. A. (2022). Automatic Speech Recognition. alikoker.com.tr. https://alikoker.com.tr/en/automatic-speech-recognition

- BibTeX: https://alikoker.com.tr/en/automatic-speech-recognition.bib
- RIS: https://alikoker.com.tr/en/automatic-speech-recognition.ris
- CSL-JSON: https://alikoker.com.tr/en/automatic-speech-recognition.csl.json