ABSTRACT
This is also known as a shelving lowpass equaliser. It gives a frequency response that at low frequencies is flat, but begins to fall as the frequency rises and approaches the cut frequency fc. It continues to fall at a basic rate of 6 dB/octave until the shelf frequency fs is reached, at which point it shelves, leveling out to a fixed gain. As with the HF-boost equaliser, unless the boost and the shelf frequency are spaced by several octaves the slope between the gain regimes will be much less than 6 dB/octave. Figure 11.9 shows the inverting form of the circuit, with its design equations. A non-inverting version of this equaliser also exists but is less flexible because it cannot have a gain of less than one.
