How does speech recognition work in an AI voice agent?
Speech recognition, also called ASR or speech-to-text, is the part of an AI voice agent that turns the caller's voice into text the language model can read. It works on short slices of audio as they arrive, producing a running transcript that is refined as more words come in, so the agent can begin working on a reply almost as soon as the caller finishes.
From sound to words
Phone audio arrives as a stream of samples, typically 8,000 per second on a standard telephone line. The recogniser converts short windows of that audio into acoustic features, and a neural network predicts the most likely sequence of words. Modern systems do this end to end in one model, rather than in the separate acoustic, pronunciation and language stages older systems used.
Streaming versus batch
Batch recognition waits for a complete recording and transcribes it all at once, which suits post-call transcripts but is too slow for live conversation. Streaming recognition emits partial results every few hundred milliseconds. Early words can change as context arrives: 'I want to see the' may become 'I want to see the 2BHK' a moment later.
Voice agents use streaming recognition during the call, and some platforms re-transcribe the full recording afterwards for a cleaner record.
What makes it hard on Indian calls
- —Narrowband telephone audio that drops higher frequencies.
- —Background noise from traffic, markets and households.
- —Code-switching between an Indian language and English within a sentence.
- —Proper nouns such as localities, project names and surnames.
- —Numbers spoken in mixed forms, such as 'pachees thousand' or 'two lakh fifty'.
How quality is measured
The standard metric is word error rate: the share of words the system got wrong, missed or inserted compared with a careful human transcript. It is useful for comparing systems on the same audio, but headline figures from different vendors are rarely comparable because they are measured on different data. A pilot on your own calls is a better guide.
Why the transcript is not the final word
The language model that reads the transcript can often correct small errors from context, just as a person understands a mumbled word. That is why a voice agent may respond correctly even when the raw transcript contains a mistake. Outpero gives you the full transcript of every call, so you can see exactly what was heard.
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Follow-up questions
Is ASR the same as speech-to-text?
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Yes. ASR, automatic speech recognition, and STT, speech-to-text, describe the same thing: software that converts spoken audio into written text. ASR is the older, academic term, while STT is more common in product documentation. In a voice agent, either name refers to the first stage of the pipeline, before the language model and speech synthesis.