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

# Control Speed and Emotion

> Learn how to control the speed and emotion of generated speech.

<Warning>
  This feature has been deprecated. Please see [the changelog](/changelog/2025#april-2025) for details.
</Warning>

Speed and emotion controls are available through the [playground](https://play.cartesia.ai) and the API in the Text-to-Speech endpoints ([Bytes](/2024-11-13/api-reference/tts/bytes), [SSE](/2024-11-13/api-reference/tts/sse), and [WebSocket](/2024-11-13/api-reference/tts/websocket)).

<Note>
  **The effects of controls vary by voice and transcript.** If you find that the controls cause artifacts in the generated speech, try reducing their strength or reducing the number of controls you have applied.
</Note>

## Playground

In the playground, you can access speed and emotion controls by clicking the "Speed/Emotion" button in the Text-to-Speech tab.

<Frame>
  <img src="https://mintcdn.com/cartesia-2650f86a/N8b057CQHGBDct9c/assets/images/speed-emotion-pg.png?fit=max&auto=format&n=N8b057CQHGBDct9c&q=85&s=f0e6ce58c828b075d43940bf14016408" width="1552" height="572" data-path="assets/images/speed-emotion-pg.png" />
</Frame>

## API

<Warning>
  This feature is currently experimental and is subject to breaking changes.
</Warning>

To use controls in the API, add the `__experimental_controls` dictionary to the `voice` object in your API request:

```json theme={null}
"voice": {
  "mode": "id",
  "id": "VOICE_ID",
  "__experimental_controls": {
    "speed": "normal",
    "emotion": [
      "positivity:high",
      "curiosity"
    ]
  }
}
```

### Speed Options

* `"slowest"`: Very slow speech
* `"slow"`: Slower than normal speech
* `"normal"`: Default speech rate
* `"fast"`: Faster than normal speech
* `"fastest"`: Very fast speech

For more granular control, you can define speed as a number within the range $[-1.0, 1.0]$. A value of 0 represents the default speed, while negative values slow down the speech and positive values speed it up.

<CodeGroup>
  ```json Using a label theme={null}
  "__experimental_controls": {
    "speed": "fast"
  }
  ```

  ```json Using a number theme={null}
  "__experimental_controls": {
    "speed": -0.1
  }
  ```
</CodeGroup>

### Emotion Options

The `emotion` parameter is an array of "tags" in the form `emotion_name:level`. For example, `positivity:high` or `curiosity`.

#### Emotion Names

* `anger`
* `positivity`
* `surprise`
* `sadness`
* `curiosity`

#### Emotion Levels

<Note>
  **Emotion controls are purely additive, they cannot reduce or remove emotions.** For example, `anger:low` will add a small amount of anger to the voice, not make the voice less angry.
</Note>

* `lowest`
* `low`
* (omit level for moderate addition of the emotion)
* `high`
* `highest`