Suggestions for a Project using DSP/Speech Processing

Hi all,

I'm working on a project that will involve the the mbed and some DSP. Our goal is to create a system with live audio processing that take voice input and change it so that the person sounds like Darth Vader. Pretty cool right? However, I have little experience with DSP (though I have working knowledge of its concepts), so I'm looking for some guidance about how to proceed, here's the general plan:

run matlab on the mbed (anyone have experience with this?), doing real time audio processing with the ADC to play around with frequency characteristics and then spit it back out using a DAC. Anyone done anything similar to this? can it be done in real time? Will this be too heavy of a load on the mbed to be done in real time?

I was also thinking of implementing another IC, such as a speech chip, to add additional vocal effects (like that kind of robotic/metallic tone Vader has) to the output after the DSP on the mbed has been done. I've found a lot of stuff that does speech creation, but I havent found much on adding effects to real voice input. Anyone done anything with this?

Any advice would be welcome.

Thanks,
Rick