Thanks for posting this. I look for Audiobooks on here for my MP3 player. I haven't tried it for dictation. If you're lucky enough to have a player (MP3 or other) that has variable speed, you can change it. For example, my SanDisk Fuze has "slow, normal, fast" for audiobooks. It does change the speech itself, the voice sounds slower, but it has that option.
"Gregg Shorthand had achieved the most extraordinary success ever attained by any system in the history of shorthand." John Robert Gregg, 1922