Parametric EQs are fairly basic in their operation. Most contain two different types of EQ. The first is hi and lo shelving filters which are akin to traditional hi-fi treble and bass controls. A hi shelf filter can increase/decrease the frequencies above a user selectable frequency. The lo shelf filter does the same for bass frequencies. The parametric part of the EQ is very similar to the shelf functions, but with a few additional tweaks. Whereas the shelf filters effect frequencies above or below their selected values, the parametric EQ has a center frequency that effects response to either side of the selected value. Visually speaking, increasing values produce a hill (or valley) in the frequency response. The "width" of the hill/valley is controlled by the "Q" control. A low Q valley produces a very narrow bandwidth hill/valley that will only effect a small number of frequencies, say 1/12 of an octave around the center frequency. A high Q will produce a very broad hill/valley that can cover 2 or 3 octaves. As a point of comparison, a graphic EQ is a parametric EQ minus the Q control.
For increased flexibility most parametrics have multiple parametric sections. Here's a link to one of the better available pro units. Manley Massive Passive. It's a stereo unit with each channel having 4 separate parametric EQs plus hi and lo filters. This unit has a feature not often seen because it allows the user to also select shelving or bell shaped curves for each individual parametric section. The pictographs give a good idea of how that control functions.
Parametric EQ was invented in the early 70s by the recording engineer George Massenburg (Linda Rondstadt, Little Feat, Lyle Lovett, etc.).
For increased flexibility most parametrics have multiple parametric sections. Here's a link to one of the better available pro units. Manley Massive Passive. It's a stereo unit with each channel having 4 separate parametric EQs plus hi and lo filters. This unit has a feature not often seen because it allows the user to also select shelving or bell shaped curves for each individual parametric section. The pictographs give a good idea of how that control functions.
Parametric EQ was invented in the early 70s by the recording engineer George Massenburg (Linda Rondstadt, Little Feat, Lyle Lovett, etc.).