The AD2055 is one of my favorite hardware equalizers. The words open, detailed, transparent, surgical and sheen come to mind when describing the AD2055. I've used this on various sounds on many mixes over the years but my favorite application is vocals. For example, I used the AD2055 on Estelle's vocals for various songs on her "Shine" album including her song "Come Over" featuring Sean Paul (produced by Supa Dups). I also used it (the Salaam Remi produced songs) on both Amy Winehouse "Frank" and "Back To Black" albums.
The AD2055 is a Class A dual mono four band equalizer with both passive and active filters. The low and high bands - Low F1 and High F4 (which can be used as shelving or parametric) are a passive filter design with 10 switchable frequencies and fully variable boost/cut of +/- 32db. The F1 selectable frequencies are 18Hz, 25, 30, 50, 72, 100, 150, 215, 300, 450Hz and the F2 frequencies are 1k5Hz, 2k5, 3k5, 5k, 7k2, 10k, 12k5, 15k, 20k, 25kHz.
The 2 mid bands - MID F2 and MID F3 are fully variable parametrics with active filters and a boost/cut range of +/- 16db with a x10 frequency multiplier. The Mid F2 covers 35hz to 450hz (350 - 4500hz with the x10 button activated. The MID F3 covers 160hz to 2khz (1.6k - 20khz with x10 activated). Both F2 and F3 bands have a Q (bandwidth) range of 0.3 to 3.0. This makes the AD2055 incredibly flexible and capable of some serious sonic surgery.
Even at extreme settings the sound of the AD2055 is extremely transparent and can easily be used for stereo/2buss applications.
For mastering I recommend the AD2077 which has additional features such as super accurate custom gold rotary switches in 0.5dB, 1dB and 2dB steps. It also has 104 switched frequencies per channel with X I0 range selectors that provide frequency selections from 12Hz to 25kHz at 1/4 octave intervals.
For more info on the AD2055: http://www.avalondesign.com/eq2055.html
The AD2055 can be purchased at various dealers including B&H Pro Audio dept. for $3,960.
and here's links to the albums on iTunes: