To change your default audio format:

Open Preferences and select the Crate section.

Choose the desired Default Audio Format from the Pop-up list.
When an item is added to one of your crates, the audio format that is selected is based on your Default Audio Format preference setting.
This can be set to one of the following values:
MP3
MP4
WAV
Open Preferences and select the Crate section.
Choose the desired Default Audio Format from the Pop-up list.