CHAPTER 5 Mixers EQ EXPLAINED The tone control or EQ ( equalization) section provides mid-frequency controls in addition to bass and treble. A typical comprehensive EQ section may have first an HF (high-frequency) control similar to a treble control but operating only at the highest frequencies. Next would come a hi-mid control, affecting frequencies from around 1 kHz to 10 kHz, the center frequency being adjusted by a separate control. Lo-mid controls would come next, similar to the hi-mid but operating over a range of, say, 200 Hz to 2 kHz. Then would come an LF (low-frequency) control. Additionally, high- and low- frequency filters can be provided. The complete EQ section looks something like that shown in Figure 5.12 . An EQ section takes up quite a bit of space, and so it is quite common for dual concentric or even assignable controls (see below) to be used. For instance, the cut/boost controls of the hi- and lo-mid sections can be surrounded by annular skirts which select the frequency. HF 0 ­4 ­8 ­12 dB 0 +4 +8 dB 5 +12 7 9 1 kHz 11 +4 +8 +12 Hi-MID ­4 ­8 ­12 Principal EQ bands The HF section affects the highest frequencies and provides up to 12 dB of boost or cut. This type of curve is called a shelving curve because it gently boosts or cuts the frequency range towards a shelf where the level remains relatively constant (see Figure 5.13(a) ). Next comes the hi-mid section. Two controls are provided here, one to give cut or boost, the other to select the desired center frequency. The latter is commonly referred to as a "swept mid" because one can sweep the setting across the frequency range. Figure 5.13(b) shows the result produced when the frequency setting is at the 1 kHz position, termed the center frequency. Maximum boost and cut affects this frequency the most, and the slopes of the LF shelf curve HF shelf curve 3 Lo-MID ­4 ­8 ­12 700 0 +4 +8 dB +12 1k