12 Voice UX Principles That Make AI Agents Feel Human

The big twelve

1. Backchannel ("mm-hm", "got it") within 600 ms.
2. Never start with "I'm an AI assistant" unless legally required.
3. Use the caller's name once, not three times.
4. Match the caller's speaking rate within ±15%.
5. Use contractions. Always.
6. Allow barge-in (the caller can interrupt).
7. Apologize once, then act.
8. Confirm critical details by repetition, not "did you say…".
9. Use a smiling voice for greeting and closing.
10. Insert short pauses before complex answers.
11. Use rising intonation only for actual questions.
12. End with a clear next step, then stop talking.