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

# Change Voice Speed

> Adjust the playback speed of an audio file

<Endpoint method="post" url="/tts/change-voice" />

Change the playback speed of an existing audio file without affecting pitch. Useful for creating faster or slower versions of audio content.

## Request

<ParamField body="audio" type="file" required>
  Audio file to modify (MP3, WAV, etc.)
</ParamField>

<ParamField body="speed" type="number" default="1.0">
  Playback speed multiplier. Range: 0.25 to 4.0

  * 0.25 = 4x slower
  * 1.0 = normal speed
  * 2.0 = 2x faster
  * 4.0 = 4x faster
</ParamField>

<ParamField body="api_key" type="string">
  Your GistMag API key (optional, but recommended for rate limiting)
</ParamField>

## Response

Returns the modified audio file as MP3.

## Credit Cost

**No credits charged** - This is a free operation for adjusting playback speed.

## Example Request

<CodeGroup>
  ```bash theme={null}
  curl -X POST https://api.gistmag.co.uk/tts/change-voice \
    -F "audio=@speech.mp3" \
    -F "speed=1.5" \
    -F "api_key=your_api_key_here" \
    --output faster_speech.mp3
  ```

  ```javascript theme={null}
  const formData = new FormData();
  formData.append('audio', audioFile);
  formData.append('speed', '1.5');
  formData.append('api_key', 'your_api_key_here');

  const response = await fetch('https://api.gistmag.co.uk/tts/change-voice', {
    method: 'POST',
    body: formData
  });

  const audioBlob = await response.blob();
  // Use the audio blob
  ```

  ```python theme={null}
  import requests

  with open('speech.mp3', 'rb') as audio_file:
      files = {'audio': audio_file}
      data = {
          'speed': 1.5,
          'api_key': 'your_api_key_here'
      }
      
      response = requests.post(
          'https://api.gistmag.co.uk/tts/change-voice',
          files=files,
          data=data
      )
      
      with open('faster_speech.mp3', 'wb') as f:
          f.write(response.content)
  ```
</CodeGroup>

## Use Cases

* Create faster versions for time-constrained content
* Slow down speech for better comprehension
* Adjust speed for different audience preferences
* Create variations of existing audio content