Voices and Previews#

Choose the conversation runtime first, then a voice it can actually use. The shared S2S interface includes both Ultravox + custom TTS and native S2S.

Two different voice catalogs#

Runtime	Voice source	Where to select it
Managed Ultravox	Compatible Ultravox, Cartesia, ElevenLabs, or Inworld catalog voices	The saved agent's `voice` object
Native OpenAI, Gemini, Grok, or Hydra	The selected model's own supported voices	`realtime.voice`, or the native provider class's `voice` option

External TTS is not a voice override for the current native S2S harness. Deepgram catalog previews and custom SDK TTS synthesis do not imply a hosted Ultravox call bridge. Check the runtime support details.

Find a compatible managed voice#

TypeScript:

const page = await supafone.labs.voices.list({ provider: "cartesia" });
console.log(page.voices);

Python:

python

page = supafone.labs.voices.list(provider="cartesia")
print(page["voices"])

REST supports additional filters and pagination:

bash

curl "https://api.supafone.ai/api/v1/labs/voices?provider=cartesia&configured_only=true" \
  -H "Authorization: Bearer $SUPAFONE_TOKEN"

Read configured, runtime_selectable, runtime_support_reason, and provider capabilities where returned. A configured voice can still be preview-only. Follow next_cursor to read more pages. Use actual catalog IDs, not example names, for live configuration.

Dynamic Voice Catalog documents brand metadata, language compatibility, REST recommendations, and the published SDK boundary.

Preview the voice, then preview the agent#

A catalog preview tests synthesis of a sample phrase:

bash

curl --get "https://api.supafone.ai/api/v1/labs/voices/preview" \
  -H "Authorization: Bearer $SUPAFONE_TOKEN" \
  --data-urlencode "voice=$CATALOG_VOICE_ID" \
  --output voice-preview.mp3

A full agent preview also exercises the conversation runtime and selected voice:

import { UltravoxS2S } from "supafone-labs";

await new UltravoxS2S(supafone).apply("northline-intake");
await supafone.labs.agents.update("northline-intake", {
  voice: { provider: "cartesia", voiceId: process.env.CARTESIA_VOICE_ID! },
});
const preview = await new UltravoxS2S(supafone).testCall("northline-intake");

python

from supafone_labs import UltravoxS2S
import os

UltravoxS2S(supafone).apply("northline-intake")
supafone.labs.agents.update(
    "northline-intake",
    voice={"provider": "cartesia", "voiceId": os.environ["CARTESIA_VOICE_ID"]},
)
preview = UltravoxS2S(supafone).test_call("northline-intake")

testCall/test_call returns connection information for the saved agent. Complete the browser session to hear it. Synthesis alone does not validate interruptions, tools, stages, or your phone carrier.

Standalone TTS is a separate surface#

Labs Cloud's /v1/voices, /v1/tts, the client's tts method, and Python's TTSProvider implementations support speech synthesis outside a hosted phone call. They are useful for audio previews and developer-owned applications. Choosing one of these backends does not replace an S2S model's native output or install it into Agent Factory. Hosted support is listed in the voice-output guide.

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