---
title: "Synthesize audio preview"
method: POST
path: "/v1/agents/{agentId}/audio-cache/{entryId}/synthesize"
tags: ["Audio Cache"]
---

# Synthesize audio preview

`POST /v1/agents/{agentId}/audio-cache/{entryId}/synthesize`

Generate a TTS audio preview using an existing cache entry's voice and provider configuration. Returns WAV audio without saving to cache, allowing you to preview how different text or tuning settings would sound before committing changes.

## Request body

- SynthesizeAudioRequest
  - `text` string, required — Text to synthesize
  - `config` VoiceTuningConfig, required — Provider-specific voice tuning settings. All fields are optional — each TTS provider uses a different subset.
    - `stability` number, float — Controls voice consistency between regenerations (ElevenLabs)
    - `similarityBoost` number, float — Controls how closely the output matches the original voice sample (ElevenLabs)
    - `speed` number, float — Playback speed multiplier. 1.0 is normal speed
    - `modelId` string — TTS model ID, specific to the provider (e.g. 'eleven_turbo_v2')
    - `engine` string — TTS engine identifier
    - `emotion` string — Emotion preset for the voice (Cartesia)
    - `volume` number, float — Output volume level (Cartesia)
    - `version` string — Model version
    - `voiceDescription` string — Natural language voice description (Hume)
    - `instantMode` boolean — Enable instant mode for lower latency (Hume)
  - `language` string — BCP-47 language tag, e.g. 'en-US'

## Response `200`

Synthesized audio

## Other responses

- `400` — Invalid request. Returned when the request body fails validation against `SynthesizeAudioRequest`, or when `entryId` is not a numeric ID.
- `401` — Unauthorized – missing or invalid API key
- `403` — Forbidden – the API key does not have `read` permission on the audio cache resource
- `404` — Resource not found

---

[API](https://skmtc.dev/poly/apis/polyai-agents-api.md) · [All operations](https://skmtc.dev/poly/apis/polyai-agents-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/poly/polyai-agents-api/revisions/76f3c606e395/schema)