You need something like a T.C. Helicon XL processor. These are the Rolls Royce of FX units There are many models to choose from depending on your exact application...I have a XL pro and it is a superb product though maybe a bit pricey compared to some other FX units. Here is a link to their site. I would think the model I have linked to would be near what you may want.
http://www.tc-helicon.com/voicelive2.asp#