What is text-to-speech?
Text-to-speech (TTS) uses computer-generated synthetic speech to read out each word of an electronic file. It can also be used to access things like menu options on electronic equipment such as computers. No recording is made and there is no audio copy of the text created, so it is an audio output of print typeface.
How is it used?
Synthetic speech is commonly available in sat nav systems and railway station announcements. It is built into the Windows and Macintosh computer operating systems, and is available on many mobile phones, including the iPhone, as well as iPods and the iPad. Third party TTS applications are available for many systems that do not have one built in.
For most people text-to-speech can be useful, or simply a fun gimmick, but for those who struggle to read the printed word, it can be an essential form of access. It has been used for many years to read electronic documents, websites and emails.
Does TTS work on eBooks?
1. eBook reading apps
Most electronic files can be read on your computer using text-to-speech software or a screen reader (an advanced TTS system which can also report additional information such as whether text is bolded or a checkbox is checked). eBooks are simply electronic files, so they are inherently accessible to 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.
Three popular apps for reading DRM-protected eBooks are Adobe Digital Editions, Kindle for PC and iBooks.
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The Kindle for PC with Accessibililty plug-in has a built-in TTS engine that can only be used to read the content of Kindle books. You still need a screen reader to move around the Kindle app and select a book to read. Note that the Kindle apps for other platforms (Mac, Android, iOS etc) do not have a TTS engine.
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The Adobe Digital Editions 1.8 preview, instead of having a built in TTS system, works with NVDA and JAWS screen readers on the Windows platform, and the built-in VoiceOver screen reader on the Mac OS X platform.
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iBooks is available for the Apple iOS devices, and works with the VoiceOver screen reader of that platform.
2. eBook reading devices
Some eBook readers have text-to-speech features built into them, including the Amazon Kindle Keyboard, the BeBook Mini V5 and the iPad.
Some rights holders have disabled the text-to-speech on their Kindle eBooks, due to concerns that it will adversely affect audio book sales or that it infringes their copyright. This only affects books read on the Kindle Keyboard, not the Kindle for PC with accessibility app.
RNIB are working hard to ensure that all eBooks have this feature turned on.
How does text to speech compare to performed audio books?
In comparison to a performed audio book, where a human 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 who is blind or partially sighted 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.
What does text to speech sound like?
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 synthetic voice on Amazon's Kindle Keyboard differs greatly to the synthetic voice used on Apple's iPad.
RNIB's synthetic voice from IVONA is, we believe, one of the best available, and it sounds very 'natural'. In comparison, the synthetic voice Eloquence that 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.
Regardless of how 'natural' text to speech can sound, it does not compare to the emotion and performance that an actor can bring to a performed audio book.
You can compare these by downloading and listening to an audio file of each type. You can also read a transcript of the text being read out, an excerpt from the novel 'Treasure Island' by Robert Louis Stephenson.