Ghosthunters and the Gruesome Invincible Lightning Ghost! Ghosthunters Series ; Book ; 2 by Cornelia Funke Copyright Year: 2007 ISBN-13: 9780439833097 Available format(s): Classic Audio Add to Bookshelf What's an Audio Format Audio format refers to the way an audiobook is recorded. Not all audiobooks have the same formats. Classic Audio: A human reading an audiobook without the text displayed. VOICEtext (H): Human narrator with text that you can follow along with as it reads. VOICEtext (S): Synthetic voice with text you can follow along with as it reads.