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

# Playback speed

> Control speaking speed in Rime synthesis using speedAlpha and inlineSpeedAlpha.

Rime allows you to customize the speaking speed of your voice agents, enabling you to:

* Enhance accessibility for diverse audiences.
* Tailor speech to specific applications (for example, slower pace for explanatory materials).
* Optimize the conversation to suit various contexts.

Learn how to adjust the speaking speed using Rime's APIs.

## Adjusting the overall speed

How you adjust overall speaking speed depends on the model.

### Coda, Arcana, and Mist v3

Use the `timeScaleFactor` parameter. A value **above 1.0 slows the audio**; a value **below 1.0 speeds it up**.

```js theme={null}
{
    ...otherParams,
    "text": "Hello, world!",
    "modelId": "coda",
    "timeScaleFactor": 0.85
}
```

<Note>
  Coda, Arcana, and Mist v3 also accept `speedAlpha`, but it works in the **opposite direction** from `timeScaleFactor` (higher than 1.0 is faster, lower is slower). Going forward we recommend `timeScaleFactor` for these models — it's the parameter we'll continue to support across future flagship models.
</Note>

<Note>
  `timeScaleFactor` works over the HTTP API only. On the WebSocket endpoints (`/ws`, `/ws2`, `/ws3`), the parameter is silently ignored — use `speedAlpha` instead.
</Note>

### Mist v2

Use the `speedAlpha` parameter. **Lower** than 1.0 is faster; **higher** than 1.0 is slower.

```js theme={null}
{
    ...otherParams,
    "text": "Hello, world!",
    "modelId": "mistv2",
    "speedAlpha": 0.85
}
```

## Adjusting the speed of individual words

<Note>Per-word speed adjustment via `inlineSpeedAlpha` is a Mist-family feature. Coda and Arcana do not support it.</Note>

To adjust the speed of individual words or phrases on the Mist family, use the `inlineSpeedAlpha` parameter. It takes a comma-separated list of speed values applied to words in square brackets.

On `mistv2` and `mistv3`, values **\< 1.0 speed up** speech and values **> 1.0 slow it down**.

<Note>On Mist v3, `inlineSpeedAlpha` and `speedAlpha` go in opposite directions — `speedAlpha` follows the modern flagship direction (higher = faster), but `inlineSpeedAlpha` follows the legacy Mist direction (lower = faster). Don't infer one from the other.</Note>

For example: “This sentence is \[really] \[fast]” with inlineSpeedAlpha “0.5, 3” will make “really” fast and “fast” slow on the Mist family.

```js theme={null}
{
    ...otherParams,
    "modelId": "mistv2",
    "text": "This sentence is [really] [fast]",
    "inlineSpeedAlpha": "0.5, 3"
}
```

## Recommendations

By effectively utilizing Rime's speed control features, you can create more varied conversational AI experiences.

* Use `speedAlpha` to adjust the overall speed of the speech.
* Use `inlineSpeedAlpha` (Mist family only) to adjust the speed of individual words or phrases.
* Experiment with different values to find the best fit for your use case.
* Be mindful that large speed adjustments may impact the naturalness and clarity of the synthesized speech.