There was a time when any hi-fi worth its salt had a little row of sliders on its front panel, a graphic equalizer. On a hi-fi these arrays of variable gain notch filters were little more than a ...

professional devices usually have 31 “bands” or filters whose centre frequencies are arranged 1/3 octave apart with the capability of amplifying or attenuating the signal by + or - 12 dB. 1/3 octave ...