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Voice Application Development for Android
Voice Application Development for Android

Voice Application Development for Android: A practical guide to develop advanced and exciting voice applications for Android using open source software

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Voice Application Development for Android

Chapter 2. Text-to-Speech Synthesis

Have you ever wondered how your mobile device can read aloud your favorite e-book or your last e-mail? In this chapter, you will learn about the technology of text-to-speech synthesis (TTS) and how to use the Google TTS engine to develop applications that speak. The topics covered are:

  • The technology of text to speech synthesis

  • Google text to speech synthesis

  • Developing applications using text to speech synthesis

By the end of this chapter, you should be able to develop apps that use text-to-speech synthesis on Android devices.

Introducing text-to-speech synthesis


Text-to-speech synthesis, often abbreviated to TTS, is a technology that enables a written text to be converted into speech. TTS has been used widely to provide screen reading for people with visual impairments, and also for users with severe speech impairments. Perhaps the best known user of speech synthesis technology is the physicist Stephen Hawking who suffers from motor neurone disease and uses TTS as his speech has become unintelligible. With the aid of word prediction technology he is able to construct a sentence which he then sends to the built-in TTS system (see further: http://www.hawking.org.uk/the-computer.html).

TTS is also used widely in situations where the user's hands or eyes are busy, for example, while driving navigation systems speak the directions as the vehicle progresses along a route. Another widespread use for TTS is in public announcement systems, for example, at airports or train stations. TTS is also used in phone-based call...

The technology of text-to-speech synthesis


There are two main stages in text-to-speech synthesis:

  • Text analysis, where the text to be synthesized is analyzed and prepared for spoken output.

  • Wave form generation, where the analyzed text is converted into speech.

There can be many problems in the text analysis stage. For example, what is the correct pronunciation of the word staring? Is it to be based on the combination of the word star + ing or of stare + ing? Determining the answer to this question involves complex analysis of the structure of words; in this case, determining how the root form of a word such as stare is changed by the addition of a suffix such as ing.

There are also words that have alternative pronunciations depending on their use in a particular sentence. For example, live as a verb will rhyme with give, but as an adjective it rhymes with five. The part of speech also affects stress assignment within a word; for example, record as a noun is pronounced 'record (with the stress...

Using pre-recorded speech instead of TTS


Although the quality of TTS has improved considerably over the past few years, many commercial enterprises prefer to use pre-recorded speech in order to guarantee high-quality output. Professional artists, often referred to as voice talent, are employed to record the system's prompts.

The downside of pre-recorded prompts is that they cannot be used where the text to be output is unpredictable—as in apps for reading e-mail, text messages, or news, or in applications where new names are being continually added to the customer list. Even where the text can be predicted but involves a large number of combinations—as in flight announcements at airports—the different elements of the output have to be concatenated from pre-recorded segments but in many cases the result is jerky and unnatural. Another situation is where output in other languages might be made available. It would be possible to employ voice talent to record the output in the various languages...

Using Google text-to-speech synthesis


TTS has been available on Android devices since Android 1.6 (API Level 4).The components of the Google TTS API (package android.speech.tts) are documented at http://developer.android.com/reference/android/speech/tts/package-summary.html. Interfaces and classes are listed and further details can be obtained by clicking on these.

Starting the TTS engine

Starting the TTS engine involves creating an instance of the TextToSpeech class along with the method that will be executed when the TTS engine is initialized. Checking that TTS has been initialized is done through an interface called OnInitListener. If TTS initialization is complete, the method onInit is invoked.

The following lines of code create a TextToSpeech object that implements the onInit method of the onInitListener interface.

TextToSpeech tts = new TextToSpeech(this, new OnInitListener(){ 
    public void onInit(int status){ 
        if (status == TextToSpeech.SUCCESS) 
              speak("Hello...

Developing applications with Google TTS


In order to avoid repeating the code in several places, and to be able to focus on the new parts as we progress to more complex applications, we have encapsulated the most frequently used TTS functionalities into a library named TTSLib (see sandra.libs.tts in the source code), which is employed in the different applications.

The TTS.java class has been created following the Singleton design pattern. This means that there can only be a single instance of this class, and thus an app that employs the library uses a single TTS object with which all messages are synthesized. This has multiple advantages, such as optimizing resources and preventing developers from unwittingly creating multiple TextToSpeech instances within the same application.

TTSWithLib app – Reading user input

The next figure shows the opening screen of this app, in which the user types a text, chooses a language, and then presses a button to make the device start or stop reading the text...

Summary


This chapter has shown how to use the Google TTS API to implement text to speech synthesis on a device. An overview of the technology behind text to speech synthesis was provided, followed by an introduction to the elements of the Google TTS API. Two examples were presented illustrating the basics of text-to-speech synthesis. In subsequent chapters more sophisticated approaches will be developed.

The next chapter deals with the other side of the speech coin: speech-to-text (or speech recognition).

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Key benefits

  • A comprehensive guide containing all the best practices for voice application development for Android
  • Progress quickly from basic apps to more advanced topics
  • Written in an easy-to-follow style with detailed descriptions of the included code examples to help you learn quickly and efficiently
  • You can download the updated code here

Description

Speech technology has been around for some time now. However, it has only more recently captured the imagination of the general public with the advent of personal assistants on mobile devices that you can talk to in your own language. The potential of voice apps is huge as a novel and natural way to use mobile devices. Voice Application Development for Android is a practical, hands-on guide that provides you with a series of clear, step-by-step examples which will help you to build on the basic technologies and create more advanced and more engaging applications. With this book, you will learn how to create useful voice apps that you can deploy on your own Android device in no time at all. This book introduces you to the technologies behind voice application development in a clear and intuitive way. You will learn how to use open source software to develop apps that talk and that recognize your speech. Building on this, you will progress to developing more complex apps that can perform useful tasks, and you will learn how to develop a simple voice-based personal assistant that you can customize to suit your own needs. For more interesting information about the book, visit http://lsi.ugr.es/zoraida/androidspeechbook

Who is this book for?

Voice Application Development for Android is for all those who are interested in speech technology and for those who, as owners of Android devices, are keen to experiment with developing voice apps for their devices. It will also be useful as a starting point for professionals who are experienced in Android application development but who are not familiar with speech technologies and the development of voice user interfaces. Some background in programming in general, particularly in Java, is assumed.

What you will learn

  • Use text-to-speech synthesis so that your device can talk to you
  • Enable your device to recognize your speech
  • Create simple voice interactions to get information and carry out commands
  • Develop a voice app that engages in a dialogue with you to collect the information required to perform a transaction
  • Use grammars to enable your app to understand the meaning behind your words
  • Make use of different languages in your apps
  • Add multimodal interaction to your apps as an alternative to speech
  • Build a voice-based personal assistant using an open source development platform for chatbots
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Table of Contents

9 Chapters
Speech on Android Devices Chevron down icon Chevron up icon
Text-to-Speech Synthesis Chevron down icon Chevron up icon
Speech Recognition Chevron down icon Chevron up icon
Simple Voice Interactions Chevron down icon Chevron up icon
Form-filling Dialogs Chevron down icon Chevron up icon
Grammars for Dialog Chevron down icon Chevron up icon
Multilingual and Multimodal Dialogs Chevron down icon Chevron up icon
Dialogs with Virtual Personal Assistants Chevron down icon Chevron up icon
Taking it Further Chevron down icon Chevron up icon

Customer reviews

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Full star icon Full star icon Full star icon Full star icon Half star icon 4.5
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Shivam Chopra Jan 28, 2014
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Really loved this book, like the way he has explained each and every aspect of Voice App Development. He has taken from the ground level. So that a beginner and a professional both can understand it.Really Recommended.
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Amazon Customer Jan 31, 2014
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
The book really helped in understanding the core concepts which are missing in documentation and also helped in the correct use of many of the API's.
Amazon Verified review Amazon
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