10 EQ Modes Explained: High Cut and Low Cut EQ
In my last Post I mentioned that some beginners get confused by terminology when they come across settings like high and low pass filters and EQ’s. It is logical, since it is a strange naming of things, but once we understand that pass quite literally means letting a range of the spectrum pass through, we can start to see the reason for using these settings. So, why would there be a different EQ mode for high and low Cut EQ’s? Well, technically we could get by with just using one or the other, since they are often synonymous with each other. A high cut EQ can work essentially the same as a low pass EQ and the same with a low cut and a high pass. A high cut EQ will remove the audio signal above the target setting, and a low cut EQ will remove the audio below the target setting. One could argue that this seems more logical than a “pass” EQ. Not everyone may catch on to the logic of a pass filter as soon as the obvious terminology of a cut EQ. But, does this mean that they are essentially the same thing, and if so, why would they be called one instead of the other?
The truth is that one EQ mode can “pass” for another (pun definitely intended). Cutting lows below a certain point is the same as allowing all audio above that point to pass. But, the factors that surround pass and cut filters can be different. Typically, a pass filter is a preset shape, and only the pass Frequency may be changed. With a cut EQ, it is possible that the same Frequencies and even same EQ shapes may be chosen as the pass filter. But, sometimes with cut, we may have a different array of frequencies and we may also have the ability to adjust the Gain, depending on the EQ. The methodology of the cut Frequency can vary, from the amount of decibels per octave that are cut to the type of filtering process used to achieve the goal. As we will see when looking at Shelf EQ’s, the selected Frequency is not the only factor determining a pass or cut filter.
The shape of the filter tends to serve a reason that some designs call the setting a cut or pass filter. Although it is true that it can designate the same thing, there is more variation involved in the potential settings of a cut EQ slope and shape, depth, and options for Gain control. Cut EQ can designate that it is offering the user the opportunity to eliminate a Shelf-type reduction of a wide range of Frequencies above or below the threshold, but it also leaves the options open to define how deep the cut is, and whether it is a soft taper or a strong brickwall cut-off.
With a pass EQ, the only factor that the user is to consider is the Frequency that serves a cut-off point, and everything beyond that threshold is to be completely gone as best served by the design. So, in its purest form, the cut and pass filters are very similar, but cut tends to share characteristics with the Shelf EQ and pass EQ, where there is some room for flexibility in shape, Gain, slope, and depth, but the bottom line is the goal to cut Frequencies to a deep setting, with an understanding that some designs allow for more flexibility, and still others may have a set cut-off filter and a separate Shelf option.