Geez, all the GPS's along with cars seem to TALK! I have yet to find an affordable I2C text to speech synthesizer. What are folks using today?
Foggy
I don't think your car is doing text-to-speech. There is a limited vocabulary, so the words are probably stored in a highly-compressed format. (There are speech formats more-compressed than MP3, and optimized for speech.)
If your navigation system is reading street names, that's probably text-to-speech, but the common words & numbers would be stored in a look-up table.
Maybe I used a poor reference to compare with my wants. I am want a synthesizer that converts text to speech, not many words/second and not one that will kill my PIC18F4550. I read that synthesizers will command a great deal of CPU time which is one reason I mentioned an SP03 which has an onboard PIC. The ONLY one I came across also came with a $90 price ticket.