Like an auto wah, where the signal level dictates the filter frequency? If so, just get a wah block and tie the modifier that is controlled by your pedal to the envelope follower. It is pretty much as Java said.
For clarification, when Java said sweep, he meant the range of your filter effect.
The envelope follower is the thing that measures your signal level and turns it into a modifier/controller.
Thanks Java..... Forgive my ignorance but Im not sure I understand how the volume of the picked note will control the filter
edit..I just reread my original post and I didnt explain very well. I want to set up a filter so that frequency that will follow volume level not just be triggered by volume and then sweep on its own