AI BriefingBuilding a Voice Agent with Twilio and ElevenLabs
Key point
Explains how to combine Twilio, ElevenLabs, and an LLM to build a voice agent capable of real-time voice responses in 20 minutes.
Details
A voice agent goes through a process of receiving a phone call, converting it to text with STT(Speech-to-Text), generating an answer with an LLM, and then outputting speech again with TTS(Text-to-Speech). Using ElevenLabs and Twilio, you can implement an agent that works with a real phone number in about 20 minutes.
The overall architecture is designed with each stage as an independent adapter structure, making it easy to swap out components.
- Twilio: Handles phone call connection and audio transmission
- ElevenLabs: Voice processing via Scribe v2 Realtime(STT) and Flash v2.5(TTS)
- LLM: Tool calling and answer text generation (OpenAI or Anthropic can be used)
In the communication flow, Twilio streams audio to the server via WebSocket in the form of base64-encoded mu-law frames, and the server forwards this to ElevenLabs' Scribe v2 to convert it to text. Afterward, the answer generated by the LLM is synthesized again with Flash v2.5 and delivered to the caller via Twilio.
For latency optimization, Scribe v2 Realtime provides fast processing speed of about 150ms, and Flash v2.5 about 75ms. In particular, at the LLM stage, which causes the biggest delay, tokens are streamed one by one so that synthesis begins before the model finishes completing the sentence, maximizing response speed.
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