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Multimodal
Voice Agents
Definition
Voice agents are AI systems that conduct spoken conversations autonomously, combining speech recognition, LLM reasoning, and text-to-speech to handle phone calls and voice interactions.
Why It Matters
Voice remains the most natural human communication channel. Voice agents can handle customer service calls, schedule appointments, conduct surveys, and provide support 24/7 without human operators. The convergence of good STT, capable LLMs, and natural TTS makes this practical for production use.
Architecture
Audio In → STT → LLM Reasoning → TTS → Audio Out
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Tool Calls (APIs, databases)Key challenge: Managing latency to maintain natural conversation flow.
Platforms
- Vapi: Developer-focused voice AI platform
- Retell.ai: Low-latency voice agents
- Bland AI: Enterprise phone agents
- Play.ai: Conversational voice platform
- Vocode: Open-source voice agent framework
Key Considerations
- Latency: Under 500ms for natural feel
- Turn-taking: Knowing when to speak vs. listen
- Error Recovery: Handling misunderstandings gracefully
- Emotion Detection: Responding to user frustration
- Compliance: Recording consent, data privacy
Use Cases
Customer support, appointment scheduling, lead qualification, surveys, outbound sales, and receptionist functions.