You can upload audio files on Mastodon, they can be any length as long as the file is under 40 mb

Supported formats: MP3, AAC, OGG, WAV, FLAC, OPUS, M4A & 3GP

To upload:

1. Log in through your server's website
2. Click 📎 paperclip icon
3. Select audio file
4. Click Edit, add a text description of the audio (for deaf people) and optionally add a custom image. If you don't add a custom image, your profile image will be shown. Click Apply.
5. Click Publish

Some apps also allow audio uploads.