Use the Mac's text-to-speech (VoiceOver) from a Processing sketch

say-out-loud.pde

// Note: this is MacOS X only, keep that in mind if you want something portable
// but it's a very easy way to prototype a project using TTS

// Possible voices: "Agnes", "Albert", "Alex", "Bruce", "Fiona", "Fred", "Kathy",
//                  "Princess", "Ralph", "Vicki", "Victoria"
// Weird voices: "Bad News", "Bahh", "Bells", "Boing", "Bubbles", "Cellos", "Deranged",
//               "Good News", "Hysterical", "Junior", "Pipe Organ", "Trinoids", "Whisper", "Zarvox"
//
// to see all installed voices, in a terminal type: `say -v ?`

// Parameters
final String voice = "Alex";
final String rate = "180"; // this must be a string (in quotes) not an int!
String sayText;

void setup() {
	// your normal setup here...
}

void draw() {
	// change this variable to what you need during the loop
    sayText = "Text to be spoken here";


    // All the code say the text, block the execution
    // of the Processing sketch until it's done, then continue (ie loop again).
    // This means that the text will be played over and over, so you may
    // want to move this under a condition
    try {
        String[] params = { "/usr/bin/say", "-r", rate, "-v", voice, sayText };
        exec(params).waitFor();
    } catch(Exception e) {
        println(e);
    }
}