Humm,
A Graphic Equalizer is basically Tone Controls that allow adjustments of the overall sound spectrum. For more on the overall sound sprectrum look at the Fletcher-Munsun Curves. Mostly a Graphic Equalizer is used to balance up a room that may have defencies. In that case you just have to adjust until it sounds pleasing to you.

In a recording after the sound is put on some medium there may be some mixing, also adjusting the overall frequency until it sounds pleasing with the cavet that if you didn't get a good recording in the first place you probably can't fix it in the mix. A Equalizer/Mixer either raises the volume or cuts it at each part of the spectrum. Equalizers may have several controls along the sprectrum, (About 50 to 15K overall). More isn't necessarily better.

Ray E. Strode