If you're experiencing issues with poor call quality or unclear voice transmission while using your C30i earbuds, there are several steps you can take to troubleshoot and potentially resolve the problem. Here's a guide to help you improve your call experience:

1. Check if there is any dirt blocking the microphone on the earbuds.

2. Ensure the earbuds are not worn incorrectly, as wearing them the wrong way can affect call quality.
 

3. If you wish to use a single earbud for calls, place the other earbud back into the charging case and close the lid.

4. It is recommended to wear both earbuds to enhance the listening experience.

By following these steps, you should be able to improve the call quality and clarity of your voice when using the C30i earbuds. Remember that maintaining your earbuds and using them as directed are key to enjoying a high-quality audio experience.