Speech-to-Speech

Convert a donor recording into a target voice while preserving delivery and timing. Speech-to-speech uses the same synthesis endpoint as synchronous TTS, but you pass SSML that references a source recording.

Quick Example

$
curl --request POST "https://f.cluster.resemble.ai/synthesize" \
>
  -H "Authorization: Bearer YOUR_API_TOKEN" \
>
  -H "Content-Type: application/json" \
>
  --data '{
>
    "voice_uuid": "55592656",
>
    "data": "<resemble:convert src=\"https://storage.googleapis.com/resemble-ai-docs-public-files/sts-donor-example.wav\"></resemble:convert>",
>
    "sample_rate": 48000,
>
    "output_format": "wav"
>
  }'

Endpoint

POST https://f.cluster.resemble.ai/synthesize

Request Body

Response

Identical to synchronous TTS responses:

1
{
2
  "audio_content": "<base64>",
3
  "audio_timestamps": {
4
    "graph_chars": ["H", "i"],
5
    "graph_times": [[0.03, 0.14], ...],
6
    "phon_chars": ["HH", "AY"],
7
    "phon_times": [[0.03, 0.14], ...]
8
  },
9
  "duration": 4.02,
10
  "success": true,
11
  "output_format": "wav"
12
}

<resemble:convert> Attributes

Tip: Store donor files in cloud storage with signed URLs and revoke them after synthesis completes.

Prompting with Speech-to-Speech

You can use the prompt attribute to guide how the donor audio is converted to the target voice. Unlike text-to-speech where the prompt is placed on the <speak> root element, for speech-to-speech conversion you must place the prompt attribute directly on the <resemble:convert> tag.

Example with Prompt

$
curl --request POST "https://f.cluster.resemble.ai/synthesize" \
>
  -H "Authorization: Bearer YOUR_API_TOKEN" \
>
  -H "Content-Type: application/json" \
>
  --data '{
>
    "voice_uuid": "55592656",
>
    "data": "<speak><resemble:convert src=\"https://storage.googleapis.com/resemble-ai-docs-public-files/sts-donor-example.wav\" prompt=\"Speak in a British accent.\"></resemble:convert></speak>",
>
    "sample_rate": 48000,
>
    "output_format": "wav"
>
  }'

The prompt attribute allows you to adjust:

• Accent or dialect (e.g. “Speak in a British accent”)
• Tone or emotion (e.g. “Speak with excitement”)
• Speaking style (e.g. “Speak in a formal tone”)

This provides fine-grained control over how the donor audio’s delivery is transformed while maintaining the original timing and prosody.