Graphic equalisers are found in just about every sound application, from room contouring to feedback control and general audio sweetening. Traditionally, much general eq'ing takes place on the faders alone, but this restricts the use of the faders at each end of the scale for further precision eq work. So we provided the Opal FCS-966 with separate LF and HF contour filters which can change an overall sound balance without disturbing a detailed room or loudspeaker response. These filters are very musical gentle boost and cut shelving filters which can be used to add (or remove) room effects that change with temperature, audience numbers or humidity. All these effects can be easily made without disturbing the critical fader settings already made. The modern generation of graphic eq's uses the Constant Q topology, pioneered by BSS Audio, which means that the filter width is constant whatever the fader gain setting. Compared to the earlier 'gyrator' style of filters, Constant Q filters provide a smoother and more predictable interaction between adjacent faders and the resulting eq curve more closely resembles the actual fader positions. Each eq fader has +/-15dB of adjustable gain, more than many competitive graphic eq's. The faders are long-throw 45mm types for precision control.