Text-to-speech (TTS) uses computer-generated synthetic speech to read out text, and is commonly used in sat navs and tannoy announcements. It is built into most new smartphones, tablets and other computers, and third party applications are available for many systems that do not have one built in. Text-to-speech can be useful for anyone, but for those who struggle to read the printed word, it can be an essential form of access.
eBooks are simply electronic files, so they are inherently accessible with text-to-speech. However, due to author and publisher concerns over copyright infringement, some eBooks are protected with Digital Rights Management (DRM), which can prevent text-to-speech software from accessing eBook content.
No new eBook readers and very few apps have text-to-speech built into them. However, the latest versions of most computer and smartphone systems contain text-to-speech which apps can make use of.
In comparison to a performed audio book, where a person reads the content, and reflects the emotion and pace of an author's work, text-to-speech can sound stilted and mechanical. A blind or partially sighted person who is used to text to speech, however, may prefer it precisely because it is not performed, as it allows them to draw their own interpretation from the text.
Someone may prefer either performed audio books or text to speech depending on their individual preferences, the nature of the material they're reading, where they are - for example, at work or at home - and even the time of day.
However, the main advantages of eBooks with text-to-speech over performed audio books is the availability, ease of access and new titles becoming available much quicker.
A large and growing number of new and existing books are made available in eBook format, which may never be made available as audio books. So eBooks that can be read by using text-to-speech have the potential to greatly increase the number of books available to those who rely on audio formats.
There is a wide range of synthetic voices available. Each allows you to change the speed to suit your preference, and sometimes choose from a number of different voices, for instance female or male.
The voice on Amazon's Kindle Fire HDX differs greatly to that used on Apple's iPad or RNIB's synthetic voice from IVONA, all of which sound very natural. Eloquence, which comes with some screen readers can sound 'robotic', but is widely liked by many blind and partially sighted people because it remains intelligible at very high speeds.
Listen to our clips of the synthetic voices used by different eBook readers with an excerpt from the novel 'Treasure Island' by Robert Louis Stephenson: