tone control formulas

[Amagic]

Hi in regards to the circuits attacted what formulas are used to calulate the gain at certain frequecies, i understand when you take out the capacitor gain= R2/R1

But with the capacitor back in doe's the formulas change, is there a way of working out the gain if for example 500Hz was inputted

Many Thanks

[Satamax]

http://www.engr.sjsu.edu/filter/Proj...fil_cosper.htm

http://www.linkwitzlab.com/filters.htm

http://www.ethanwiner.com/filters.html

http://www.electronics-tutorials.com...ss-filters.htm

http://www.antonine-education.co.uk/...rc_filters.htm

It's worth to read it all, but the formula for the reactance is here. http://www.antonine-education.co.uk/...ve_filters.htm

HTH and good reading