> ## Documentation Index
> Fetch the complete documentation index at: https://docs.finesse.flamapp.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Synthesize parameters

> The request body shared by the /speak and /stream endpoints.

Both [Synthesize speech](/voice-api/synthesize-speech) and [Stream speech](/voice-api/stream-speech)
accept the same JSON body.

<ParamField body="text" type="string" required>
  The text to synthesize. Maximum **10,000 characters**. Requests over the limit return `400`.
</ParamField>

<ParamField body="language" type="string">
  BCP-47 language code, e.g. `en`, `hi`, `es`. Defaults to the voice's `primary_language`.
</ParamField>

<ParamField body="output_format" type="string" default="wav">
  Output encoding:

  | Value | Description |
  | - | - |
  | `wav` | Self-contained WAV file (recommended for playback/download). |
  | `s16le` | Signed 16-bit little-endian PCM (headerless). |
  | `s24le` | Signed 24-bit little-endian PCM (headerless). |
  | `s32le` | Signed 32-bit little-endian PCM (headerless). |
  | `f32le` | 32-bit float little-endian PCM (headerless). |
  | `f64le` | 64-bit float little-endian PCM (headerless). |

  The headerless PCM formats need a known `sample_rate` and channel count to play.
</ParamField>

<ParamField body="sample_rate" type="integer" default={24000} initialValue={24000}>
  Output sample rate in Hz. Defaults to the provider's native rate (`24000`); values above it are
  upsampled. The actual rate is returned in the `X-Sample-Rate` response header (and the `start`
  event for streaming).
</ParamField>

<ParamField body="num_step" type="integer" default={32} initialValue={32}>
  Number of inference steps, `1`–`32` - a quality vs. latency trade-off. Provider default (`32`) if
  omitted.
</ParamField>

<ParamField body="expressiveness" type="number" initialValue={0.5}>
  Style/expressiveness control, `0.0`–`1.0`. Provider default if omitted.
</ParamField>

```json Example body theme={null}
{
  "text": "The quick brown fox jumps over the lazy dog.",
  "language": "en",
  "output_format": "wav",
  "sample_rate": 24000,
  "expressiveness": 0.5
}
```


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