how can i draw an envelope for low pass in sonar?

[r0cker]

hi there, thanks for checking this. this seems like quite a basic question but i can't figure it out. basically i want to be able to draw an envelope for the frequency of a low pass filter accross a clip so that as the clip plays the frequencies that can be heard change with the envelope like they do in house tracks for example where the filters open and close over a loop. i have been using the fxeq effect but the low pass in this only goes up to 200hz and i want something that can filter the whole range so that if i have a loop of say a disco track when the enevlope is at the top i can hear everything and then as it goes down i will lose hi hats then guitars and end up with only bass. if anyone can help i would be much appreciative.
thanks in advance
r0cker