Graphic Equalizer Pro is a professional real-time graphic equalizer for Windows 9x/Me/NT/2000/XP. It will add up to 12 dB of boost or cut at any of 15 bands centered around the International Standards Organization (ISO) 2/3 octave frequencies from 20Hz to 20kHz. This two channel system offers completely independent channel control.
http://headwize.com/projects/showfile.php?file=anwida_prj.htm
Uses a single chip, IC BA3812L, which is a five-point graphic equalizer that has all the required functions integrated onto one IC.
http://www.electronic-circuits-diagrams.com/audioimages/audiockt12.shtml
There is approximately +/-20dB of boost or cut at frequencies of 50Hz, 1kHz and 10kHz.
http://www.zen22142.zen.co.uk/Circuits/Audio/3band.htm