Hi @Bailly_1, if you have a JSON field containing a base64-encoded file (like audioContent from your screenshot) you could convert it into a binary using the Move Binary Data node like so (the first two nodes in this example flow just prepare dummy data to work with):
Make sure to enable the Data Is Base64 option, specify the correct MIME type (audio/mpeg for MP3) and a valid filename and you should get a proper audio file: