OS X Mountain Lion's Text to Speech
Your Mac can speak to you using Text to Speech, which converts on-screen text to spoken words. If you’ve used Text to Speech in earlier versions of OS X, you’ll find that it’s pretty much unchanged in Mountain Lion.
Why might you need Text to Speech? Because sometimes hearing is better than reading.
You can configure this feature in the Speech System Preferences pane:
Open the System Preferences (from Launchpad, the Applications folder, Dock, or Apple menu), click the Speech icon, and then click the Text to Speech tab.
Choose one of the voices in the System Voice pop-up menu to set the voice your Mac uses when it reads to you.
Click the Play button to hear a sample of the voice you selected.
Use the Speaking Rate slider to speed up or slow down the voice.
Click the Play button to hear the voice at its new speed.
Select the Announce When Alerts Are Displayed check box if you want to make your Mac speak the text in alert boxes and dialogs.
You might hear such alerts as The application Microsoft Word has quit unexpectedly or Paper out or not loaded correctly.
Click the Set Alert Options button to choose a different voice to announce your alerts — the phrase your Mac speaks (Alert, Attention, Yo, dude, and the like) when alerting you.
You can also set the delay between the time the alert appears and when it’s spoken to you.
(Optional) If you like, select either of these two check boxes: Announce When an Application Requires Your Attention or Speak Selected Text When the Key Is Pressed.
They both do what they say they’ll do. In the case of the latter, you assign the key you want to press by clicking the Set Key button.
(Optional) If you want to have the clock announce the time, click the Open Date & Time Preferences button, and you’re whisked to that System Preferences pane; then click the Clock tab and select the Announce the Time check box.
Now, to use Text to Speech to read text to you, copy the text to the Clipboard, launch TextEdit, paste the text into the empty untitled document, click where you want your Mac to begin reading to you, and then choose Edit→Speech→Start Speaking. To make it stop, choose Edit→Speech→Stop Speaking.
Another great place Text to Speech is available is in the Safari web browser. It works the same as TextEdit but you don’t have to paste — just select the text you want to hear and choose Edit→Speech→Start Speaking.