The Eventide Omnipressor does what you are requesting with additional versatility.  We wrote a tutorial on how to create this with a VSIG program.  I can't seem to find it on our own web site but there is a copy here:

http://pdf.textfiles.com/manuals/STARINMANUALS/Eventide/Manuals/White%20Papers/The%20Omnipressor%20Redux-The%20Anatomy%20of%20a%20''Preset''.pdf