Voice AI Latency
Voice AI latency is the total time between the user finishing a sentence and hearing the agent begin to respond — the single most important quality metric for conversational 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-powered system that has real-time spoken conversations — over a phone call, a web widget or a SIP trunk — using speech recognition, a language model and speech synthesis.
Voice AI is the umbrella term for AI systems that understand and generate human speech in real time — powering voice assistants, phone agents, voice chatbots and real-time translation.
Conversational AI is the category of AI systems designed to interact with humans in natural language, across chat, voice, email and messaging — using NLU, LLMs and tool-calling to hold multi-turn conversations that actually accomplish work.
IVR is a rigid scripted decision tree (press 1 for sales). Voice AI is a natural-language agent that understands free-form speech, uses LLM reasoning, and calls tools to take real actions.
BYOK means you bring your own API keys for the LLM, STT and TTS providers, and the voice AI platform routes usage through your accounts instead of bundling the provider costs into its own pricing.
BYON means you bring your own phone number — via a Twilio, Vobiz or Exotel account — and connect it to the voice AI platform via SIP, instead of renting a number from the platform itself.