Real-Time Voice AI: How Sub-Second Latency Changes Everything

Why Latency Is the Most Important Metric in Voice AI

In text-based AI, a 2-3 second response delay is acceptable. In voice conversations, it is a deal-breaker.

Human conversation has a natural turn-taking rhythm. When you finish speaking, you expect a response within 200-500 milliseconds. Longer pauses feel awkward. Pauses beyond 1 second feel broken. Callers start saying "Hello? Are you there?" — and eventually hang up.

For AI voice agents, end-to-end latency — the time from when a caller stops speaking to when they hear the AI respond — determines whether the conversation feels natural or robotic.

The Latency Budget

A sub-500ms response requires careful optimization at every stage:

Stage	Target Latency	What Happens
Speech end detection	100ms	Detect that caller has finished speaking
ASR (transcription)	50-100ms	Convert speech to text (streaming)
LLM processing	150-250ms	Generate response (time to first token)
TTS synthesis	50-100ms	Convert text to speech (streaming)
Network transit	20-50ms	Audio delivery to caller
Total	370-600ms	Within natural conversation range

How CallSphere Achieves Sub-500ms Latency

1. Streaming everything: ASR, LLM, and TTS all operate in streaming mode. The TTS starts speaking before the LLM finishes generating.

2. Optimized model selection: Smaller, faster models handle simple interactions. Larger models are reserved for complex reasoning.

3. Edge infrastructure: Critical processing runs on edge servers close to the telephony infrastructure, minimizing network latency.

4. Predictive processing: The system begins generating likely responses before the caller finishes speaking, discarding predictions that don't match.

5. Connection pooling: Pre-warmed connections to LLM providers eliminate cold-start delays.

The Business Impact of Latency

Every 100ms of added latency reduces caller satisfaction measurably. At 2+ second delays:

• Callers begin to disengage
• Conversation quality drops
• Callers talk over the AI, creating confusion
• First-call resolution rates decrease

Measuring Latency in Production

CallSphere monitors latency in real time with P50, P95, and P99 metrics:

• P50: 380ms (median response time)
• P95: 520ms (95th percentile)
• P99: 750ms (99th percentile)

FAQ

Why do some AI voice agents feel slow?

Most AI voice agents process each stage sequentially — wait for full utterance, transcribe, process with LLM, synthesize full response, then play audio. This creates 2-4 second delays. CallSphere uses streaming at every stage to eliminate these gaps.

Does lower latency cost more?

Not necessarily. CallSphere's architecture achieves low latency through engineering optimization, not by using more expensive models. Our flat monthly pricing includes this performance.