If you have a big library of Kindle books, Amazon is hoping you'll spend a little extra for the audio versions.
A new service from Amazon, called Matchmaker, scans your Kindle book library and offers a audiobook "upgrades" at discount prices. Upgrades cost as little as $1 for free public domain books, but prices for other books can vary.
Amazon also says it will offer one book with audio narration for free every month. (This month's selection is The Sign of Four by Sir Arthur Conan Doyle.)
In a particularly nifty touch, all books listed by Matchmaker support Amazon's Whispersync for Voice service, which automatically syncs pages and audio progress across all devices, so you can switch back and forth between text and voice. The audio editions are provided by Audible, which Amazon acquired in 2008.
Keep in mind that some books come with free text-to-speech, which you can access through the menu icon on Kindle e-readers (except those that don't support audio output) and through the "Aa" view button on Kindle Fire tablets. However, not all rights holders support this feature. In fact, when Amazon tried to offer free text-to-speech for all ebooks in 2009, the company changed course in response to publisher outcry, and now lets publishers disable the feature on a title by title basis.
Matchmaker is one of several moves Amazon has made recently to offer multiple forms of consumption for the same piece of content. This month, a service called Matchbook will provide free ebook versions of past and future print versions. Amazon also provides free MP3s to customers who purchase albums on CD or Vinyl.