10 EQ Modes Explained:  Fixed “Q” width versus Variable “Q” width  EQ

What EQ Mode is right for the job? Should you use an Equalizer that has fixed Frequency positions or one that is freely selectable? Should you use an EQ that can switch between various types of filters, or has a limited, but well chosen, set of precise settings? Do you want to work within a system of choices that always works well but also helps you to place your signature on your sound, or do you want complete flexibility to make independent choices at every turn, with the potential that many different types of music have an excellent result with an indistinguishable trademark in your artistic choices? There is no single correct answer to these questions. It is just as justifiable to mix and master with an artistic touch that is complimentary and well-suited to each mix that also gives a nod to your personal style as it is to work with absolute precision and surgical care, letting nothing but the artist’s best efforts shine through, never showing favor to one adjustment over another from song to song, album to album. These choices are central to the equipment that will serve us best.

Equalizers that have a Fixed “Q” width are not necessarily as limiting to a person’s options as one might think. A Fixed “Q” Equalizer may also have Fixed Frequencies, or the Frequencies may be fully adjustable from one range to another. There are no set rules from one EQ type to the next as to whether they must have an adjustable “Q” width. Not only does it make a difference if the “Q” can be adjusted or not, but for a Fixed EQ, we will make decisions based on just how wide the “Q” is set. Typically, “Q” has little significance  when an EQ has multiple settings in its high and low Shelf settings. A Shelf setting typically will reach all the way to the end of the Spectrum.

Normally, when an EQ has a Fixed “Q” width, the “Q” is wide enough to affect the full width between one point and the next, with a smooth curve depth, meaning that the top of the mountain is rounded off to keep Gain adjustments smooth. At its deepest or steepest Gain, it will narrow steadily but still remain a smoother transition than if it were adjustable to a narrower “Q”. In very rare exceptions, an EQ may be marked at a wider “Q” than others. An example is the NSEQ-2, which has a very wide interpretation of “Q” width. Even though it is marked at standard options, it is extremely smooth, and wide. Even at its narrowest setting, which is incredibly useful for mixing and mastering, it is not as sharp and narrow as an EQ like the Sontec, or even more the Amek 9098.

We tend to think of a Variable “Q” as being the most flexible, and in most ways this is true. If the Frequency and the “Q” width are both Variable, then we can assume that any Frequency within the marked range can be broadly the center point that is adjusted, or can be sharply targeted for pinpoint removal. 

With Variable “Q” width, you have a bit more to learn about your EQ and its range of personality. You may not find yourself using the exact same settings as often and for as many similar routines, so I always recommend taking time to learn the sound of your equipment, whether real or virtual. Load up sounds, songs, or tracks as “test” tracks that you are familiar with. Before you use an EQ that has tons of freely selectable positions, test it out with a lot of care. How does the sound change from wider “Q” to narrow “Q”? Does it sounds very similar or does it go from very smooth to extremely precise. Some EQ’s increase a great deal in Gain the more narrow the “Q” selected. You may be used to using something at a medium “Q” at 5dB for boosting vocals or scooping guitars, and then you run into a place where there is unwanted resonance on a similar Frequency; not an artistic decision but a corrective issue that needs attention. That 5dB is likely to narrow at the start of the slope in a similar fashion to the medium “Q” you are used to, but as it often sharpens to a point at higher Gain settings, it reaches much more signal increase or decrease, and you may be removing more than anticipated. It is not as easy to design the perfect Variable “Q” width EQ as one might think.

The sonic results of one exact shape to the next is amazingly different. Narrow “Q” is good to have in some form, since it is hard to reduce serious trouble areas without a good sharp point that goes into deep Gain. This is not an easy task in analog or digital form. I can speak to this, as I was personally not satisfied with any result, analog or other, for extreme surgical EQ, so I set out to design my own. I created my Mastering Suite Equalizer that uses my own process that I created specifically for addressing surgical EQ for mastering music at 44.1kHz. The Amek 9098 is an extremely close second to having some of the most incredible EQ shapes, including very sharp narrow “Q” that works well, especially for tricky mixing but also in some Mastering scenarios. A fairly close third would have to be the Sontec and then the GML, which are both good enough to be desert island EQ’s. In any case, when you reach for a narrow “Q” width, listen for what else is getting removed from the signal and not just the part that needs to go. Also, listen for any resonance or strange artifacts coming from sympathetic Frequencies.

My final recommendation to you when using an EQ that has Variable “Q” width is to make use of the settings that sit between typical “Q” widths. Namely, you have EQ’s that contain typical fixed “Q” and you have EQ’s that contain wider than normal “Q” width, and you have Variable “Q” that can supply the narrow band needed to tricky audio surgery. But, those settings somewhere in between the widest setting and regular setting are not found as often in standard tracking, mixing, and bus EQ’s, as is the case with that range between mid “Q” and narrowest. Listen to these settings and become familiar with them, and train your ears to send a signal to your mind, so as to remember what affect these settings have on the audio signal. These settings will have their moments to come in handy.