Speech-to-Text Models: How They Work
๐ค Speech-to-Text Models: How They Work
Speech-to-Text (STT) — also called Automatic Speech Recognition (ASR) — is the technology that converts spoken language into written text. These models are used in voice assistants, transcription tools, customer service, and more.
๐ง Step-by-Step Breakdown
1. Audio Input
The user speaks into a microphone.
The audio is recorded as a waveform — a digital signal that represents the sound.
2. Preprocessing
The waveform is cleaned: removing background noise, normalizing volume, etc.
The audio is broken into small time segments (called frames).
Then it’s converted into features like:
MFCC (Mel Frequency Cepstral Coefficients)
Spectrograms
These features represent how sound frequencies change over time.
3. Acoustic Model
This model maps sound features to phonemes — the smallest units of sound in a language.
Deep learning models like Convolutional Neural Networks (CNNs) or Recurrent Neural Networks (RNNs) are often used here.
4. Language Model
Once phonemes or word parts are recognized, a language model helps make sense of them.
It predicts the most likely sequence of words, correcting errors and improving accuracy.
Modern systems use transformers (like BERT or GPT) for this step.
5. Decoder
The decoder combines information from the acoustic model and the language model.
It outputs the final written text that represents what was spoken.
⚙️ Types of STT Models
Traditional Models: Use separate components (acoustic, language, pronunciation models).
End-to-End Models: Use a single deep learning model (like RNN-Transducer, CTC, or Transformer-based models) to directly map audio to text.
๐งช Popular Architectures
DeepSpeech (by Mozilla) – Based on RNN + CTC loss.
Wav2Vec 2.0 (by Meta) – Uses self-supervised learning on raw audio.
Whisper (by OpenAI) – A transformer-based model trained on many languages and tasks.
✅ Real-World Applications
Voice assistants (Siri, Alexa, Google Assistant)
Live captions
Call center analytics
Dictation tools
Meeting transcription (like Zoom or Otter.ai)
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