Variable High pass filter?

[ayearofholidays]

Hi there, I would like to insert a variable high pass filter into an audio circuit, like how in large mixing consoles there's sometimes a variable high pass filter after the gain. I would like it to function similarly, rolling from 20Hz and up. Ideally I'd like to be able to figure out the high limit frequency using formulas. I've been experimenting by reversing a working Low pass filter, and adjusting values to try and dial it in right, but have been haven't been so successful. Ideally simpler is better, using just passive components.

Any help would be fantastic. Thanks!

[Minion]

Use this calculator to figure out your filter frequency ....

http://www.muzique.com/schem/filter.htm

then replace the resistor with a Pot and it will change the cut off frequency ....