I was trying to free up some disk space on my Mac, so I ran Disk Inventory X to help me find big files I could delete. I found a pretty big (669MB) file called /System/Library/Speech/Voices/Alex.SpeechVoice/Contents/Resources/PCMWave. I suspected “Alex” was probably one of the voices that can be used with the Mac’s text-to-speech feature, and that turned out to be right: If you go to System Preferences > Speech, you can find Alex there.
The PCMWave file for Alex is much bigger than the PCMWave file for any other voice, so I wasn’t surprised to find that Alex sounds far more realistic than any other voice. Nonetheless, I’m gonna kill him, because he is taking too much of my disk space.
In any case, I amused myself by listening to all the voices. Try clicking “Show More Voices” – the “Deranged” voice made me laugh out loud.