The Speech Synthesis Api: An Introduction

by admin Date: 05-02-2014 javascript programming webdev api

Today we’re going to focus on the Speech Synthesis API, which uses system libraries to speak, making the Web considerably more accessible.

NOTE: We have to consider that the API is fairly new, so not widely supported. The Speech Synthesis API is supported in Chrome 33+ and Safari. At the time of writing, the stable channel of Chrome is at version 32 so you will need to be running either the Chrome Dev channel or Chrome Canary to see this in action.

The simplest way to use this API is to pass a string to the SpeechSynthesisUtterance object and then use the speak method to have the computer say the string:

var message = new SpeechSynthesisUtterance(‘Hello World!’);  


Now, let's dig a little deeper to see how we can pass the attributes to modify the SpeechSynthesisUtterance object:

  • Text: this is the simplest, and the one we’ve already used.
  • Lang: this attribute will specify the language the synthesis should use (if nothing is specified it falls back on the document default).
  • VoiceURI: specifies the voice and the synthesis service you want to use.
  • Volume: the volume of the speech, from 0 to 1.
  • Rate: the speed at which the voice will speak. Values of 0 to 10 are permissable, but 1 is normal, 2 is double speed, 3 is triple speed and so on, so that 10 would be far too fast.
  • Pitch: the pitch of the voice ranging from 0 to 2.

To demonstrate, we’ll set up a form to determine the text, rate, pitch and volume:

<input type=“text” id=“speech"/><label for=“volume”>Volume</label>  
<input type=“range" max="1" min="0" step="0.1" value="1" id="volume">  
<label for=“rate”>Rate</label><input type=“range" max="5" min="0" step="0.5" value="2.5" id="rate"> 
<label for=“pitch”>Pitch</label><input type="range" max="2" min="0" step="0.1" value="2" id="pitch">  
<button id="talk">Speak</button>

So the first thing we need to do when it comes to the jQuery is to attach a click event to our talk button and then create a new instance of the SpeechSynthesisUtterance:

$("#talk").click(function() {   
var msg = new SpeechSynthesisUtterance();  });

After this is done we need to get the available voices, select the one we want to use and also set the voiceURI:

var voices = window.speechSynthesis.getVoices(); 
msg.voice = voices[10];   msg.voiceURI = 'native';

After this is done we need to move on to the attributes that will rely on user input and for that we will need to get the values of each input in our page using the .val() jQuery method, starting with the volume :

msg.volume = $(‘#volume’).val();

The method is the same for all the other inputs we have:

  msg.rate = $('#rate').val();  
msg.pitch = $('#pitch').val();    
msg.text = $('#speech').val();

Now all we really need to do in order to wrap this little application up is to set the language attribute and in this case I will use plain US English and then use the speechSynthesis.speakmethod to have the computer say the text with the settings we passed:

msg.lang = 'en-US';  speechSynthesis.speak(msg);

And that’s about all we needed to create a simple application using the Speech Synthesis API, this is the full code:

$("#talk").click(function() {    
var msg = new SpeechSynthesisUtterance();    
var voices = window.speechSynthesis.getVoices();   
 msg.voice = voices[10];     
msg.voiceURI = 'native';  
msg.volume = $('#volume').val();  
 msg.rate = $('#rate').val();   
 msg.pitch = $('#pitch').val();    
msg.text = $('#speech').val();    
msg.lang = 'en-US';    
speechSynthesis.speak(msg);  });


And you can also see a demo here.



Original post by Sara Vieira

by admin Date: 05-02-2014 javascript programming webdev api hits : 9916  

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