Voice Agent TTS Controls

If you’re building with the Voice Agent API, Aura-2’s TTS voice controls — speed, pronunciation, and pacing — work inside your agent pipeline. Where you apply each control depends on what it does and what context the decision needs.

Where each control belongs

Speed: configure once at the session level

Speed is a session-level setting on the agent’s speak provider. Configure it when you initialize the agent, and every response from the agent uses that rate.

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{
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  "type": "Settings",
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  "agent": {
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    "speak": {
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      "provider": {
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        "type": "deepgram",
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        "model": "aura-2-thalia-en",
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        "speed": 0.9
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      }
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    }
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  }
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}

speed accepts a float between 0.7 and 1.5 (default 1.0). For Spanish voices the recommended range is 0.9–1.5; values below 0.9 may introduce disfluencies. See TTS Models for the full parameter reference and TTS Voice Controls for the underlying behavior.

A consistent session-level speed is useful for agents that serve accessibility-sensitive audiences, or any conversation where pacing should stay steady throughout the call.

Pronunciation and pacing: handle them in the LLM prompt

Pronunciation overrides and pause cues are most effective when the LLM produces them — not when they’re added downstream — because both depend on the meaning of the surrounding text.

• Pronunciation needs context to handle heteronyms. Words like lead (the metal vs. to guide), read (present vs. past), bass (fish vs. instrument), or Polish vs. polish are spelled identically but pronounced differently. Only the LLM, which has the full conversational context, can decide which IPA override to apply for a given utterance. A static lexicon applied after the fact will mispronounce these words whenever the wrong sense is meant.
• Pacing needs to match what’s being said. Aura-2 takes pacing cues directly from punctuation: commas and periods produce short pauses, ellipses (...) produce longer ones, and digits separated by periods slow down readback for phone numbers, account numbers, and IDs. Asking the LLM to produce well-punctuated output is more reliable than post-processing a flat string. See Text to Speech Prompting for the full set of pacing techniques Aura-2 supports.

Put your pronunciation map and pacing rules in the system prompt and the Voice Agent passes the LLM’s output through to Aura-2 unchanged.

Example system prompt snippet

When saying the following terms, use these inline pronunciation controls so the
voice model produces the correct phonetic output:
- dupilumab → {"word": "dupilumab", "pronounce": "duːˈpɪljuːmæb"}
- adalimumab → {"word": "adalimumab", "pronounce": "ˌædəˈlɪmjuːmæb"}
When reading back phone numbers, account numbers, or order IDs, group digits in
twos or threes and separate each group with a period to introduce a short pause.
For example, prefer "555. 867. 5309" over "5558675309".

This keeps your pronunciation map and pacing rules in the LLM layer, not in a separate lexicon or orchestration config. To add a term, edit the prompt — no redeploy required.