The Brimstone Key Grey Griffins : The Clockwork Chronicles; Bk. 1 by Derek Benz Copyright Year: 2010 ISBN-13: 9780316045223 Available format(s): Classic Audio Log in to read 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.