Voice AI Latency
Voice AI latency is the time between the user finishing a sentence and hearing the agent respond — the most important quality metric for voice AI.
Voice AI latency is the end-to-end delay between when a user finishes speaking and when they hear the voice AI agent begin to reply. For natural-feeling conversation the target is 500–800ms total, which is split across STT (~100–200ms), LLM time-to-first-token (~150–400ms), TTS time-to-first-audio (~150–300ms), and network round-trip. Above 1.2 seconds conversation feels robotic; above 2 seconds the agent feels broken.
Why it matters
Humans perceive a pause of 800ms+ as a stall. A voice AI agent with 1.5s latency is usable but feels obviously artificial. A voice AI agent with 400ms latency feels like talking to a sharp human — which is the whole point of voice AI in the first place.
How to reduce latency
- Streaming STT: begin transcribing while the user is still speaking, not after.
- Streaming LLM: use an LLM that starts emitting tokens within 150ms. Groq-hosted models are strongest here.
- Streaming TTS: pipe tokens into TTS as the LLM generates them, not after. TTFA (time-to-first-audio) <300ms is achievable with providers like ElevenLabs Turbo and Cartesia Sonic.
- Regional deployment: host as close to your user as possible. For India, Mumbai region is the default.
- Provider routing: pick the fastest provider for each layer of the stack per workload.
Related
More definitions
A voice AI agent is an AI system that holds real-time spoken conversations via phone, web or SIP — combining speech recognition, an LLM and speech synthesis.
Voice AI is the umbrella term for AI that understands and generates human speech in real time — powering voice assistants, phone agents and translation.
Conversational AI is the category of AI that interacts with humans in natural language across chat, voice, email and messaging — using NLU, LLMs and tools.
IVR is a rigid scripted tree (press 1 for sales). Voice AI is a natural-language agent that understands free-form speech, reasons and calls tools.
BYOK lets you bring your own LLM, STT and TTS API keys so a voice AI platform routes usage through your own provider accounts instead of billing it through the platform.
BYON lets you bring your own Plivo phone number and connect it to the voice AI platform instead of renting one.