CHAPTER 5 Mixers Filters High - and low-cut filters provide fixed attenuation slopes at various frequencies. Figure 5.13(d) shows the responses at LF settings of 80, 65, 50, 35 and 20 Hz. The slopes are somewhat steeper than is the case with the HF and LF shelving curves, and slope rates of 18 or 24 dB per octave are typical. This enables just the lowest, or highest, frequencies to be rapidly attenuated with minimal effect on the mid band. Very low traffic rumble could be removed by selecting the 20 or 35 Hz setting. More serious low-frequency noise may require the use of one of the higher turnover frequencies. High-frequency hiss from, say, a noisy guitar amplifier or air escaping from a pipe organ bellows can be dealt with by select- ing the turnover frequency of the HF section which attenuates just sufficient HF noise without unduly curtailing the HF content of the wanted sound. STEREO LINE INPUT MODULES In broadcast situations it is common to require a number of inputs to be dedicated to stereo line level sources, such as CD players, electronic musical instruments, etc. Such modules are sometimes offered as an option for multitrack consoles, acting as replacements for conventional I/O modules and allowing two signals to be faded up and down together with one fader. Often the EQ on such modules is more limited, but the module may provide for the selection of more than one stereo source, and routing to the main mix as well as the multitrack. It is common to require that stereo modules always reside in special slots on the console, as they may require special wiring. Such modules also used to provide facilities for handling LP turntable outputs, offering RIAA equalization. Stereo microphone inputs can also be provided, with the option for MS (middle and side) format