One of my favorite new features of Leopard is the new professional voice they have included. “Alex”, is the new voice of Mac OS X. Before you read any further listen to this sample: Alex voice test A (mp3) or this one: Alex voice test B (mp3).
How it works: Voice synthesis on the Mac has been around for more than 20 years now, but outside of screenreading and special applications it’s never been a marquee feature (that is, if you don’t count Talking Moose — now once again available for OS X. Woot!). Even though the Macintalk and Speech Manager voices have improved a lot over time, the best of them still sound distressingly artificial.
Enter Alex, a dramatically more comprehensible voice that includes fine breath and pause control to enhance understandability, especially for high-speed reading; you can listen to a sample of Alex at this post. From the samples of Alex that I’ve heard, he compares favorably with high-end synthesis voices like AT&T’s Natural Voice and Cepstral. For anyone using VoiceOver or wanting to be able to track information while not watching the computer, Alex is a natural.” — TUAW.com post
One interesting thing is that the file that contains “the voice” is the largest single file installed on your Mac with Leopard, weighing in at 670 meg (/System/Library/Speech/Voices/Alex.SpeechVoice…).