Voice activity detectionVAD
Voice activity detection (VAD) is the technique of detecting when someone is speaking versus when there is silence or background noise. It lets software start and stop recording automatically.
A VAD model is small and fast, and runs continuously on the audio stream without transcribing anything: its only job is a yes/no answer to "is this speech?". Dictation tools use it for hands-free modes (start when speech begins, stop at a pause) and to trim silence before the recognizer runs.
A well-behaved implementation only arms the microphone when you ask it to, and discards audio that never became a dictation.
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