How to Mix and Master with EQ – 10 Equalizer Modes – Part Eight - CDSoundMaster.com

Audio Recording with Equalizers – 10 Equalizer Modes – Part Eight – 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.

How to Mix and Master with EQ – 10 Equalizer Modes – Part Eight - CDSoundMaster.com

Audio Recording with Equalizers – 10 Equalizer Modes – Part Eight – 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.

How to Mix and Master with EQ – 10 Equalizer Modes – Part Seven - CDSoundMaster.com

Audio Recording with Equalizers – 10 Equalizer Modes – Part Seven – High Pass and Low Pass EQ

Many people start recording their own music and learning the basics in mixing because they have an idea for a song, and others get involved because they have played an instrument for some time and want to record themselves in the context of a song with other instruments. Still others join a band, and once they sound decent they want to document their efforts, and some like to sing and write lyrics and try their hand at making their own tunes, either with MIDI or samples. Whatever road that gets them there, if we are talking about the self-taught beginning recordist, one thing that typically mystifies the early learner is the high pass/low pass filter or Equalizer.

They might have an easy grasp on what an Equalizer is, and what makes for different Frequencies, Spectrum, Gain, among other vocabulary. But, high and low pass may not automatically make sense. Especially if they learn about “pass” at the same time as they learn about “cut” they may be even more thrown for an answer.
The truly simple explanation for high and low pass EQ is to take it for face value. A high pass Equalizer allows everything above a certain Frequency to “pass,” meaning that all of the signal above that setting will remain and will not be removed. For example, a high pass EQ set to 100Hz means that everything from 101Hz and up will remain. This also means that everything below 100Hz will be removed.

The same concept applies to low pass EQ. In this case, the low signal spectrum is going to be allowed to pass. So, in the same situation, if a low pass EQ was set to 100Hz, we would no longer see any audio above 101Hz, thus we would only hear low Frequencies.

The “pass” EQ is designed to isolate only what is needed and to remove everything that is causing trouble at a fixed point. Because it can make a very strong statement and a very obvious change to the signal, the “pass” point is usually not set, but is usually given several fixed Frequency options. These are usually chosen at points that are known to have typical audio issues. One point might be set to remove low end rumble, and another may be set to reduce grounding noise or audio interference hum. Another setting may be set below our usual hearing level just to clear any noise that is not intended just in case it is there. Higher Frequency high pass filters, like those above 80Hz, sometimes as high as 150Hz or even 200Hz help to clarify a signal that does not rely heavily on low Frequency content. This could be anything from a mid-to-upper piano part or vocal, a guitar or cymbal, and numerous other items. A pass filter can be used on an effect channel like reverb or time-based effects like delay or chorus or flange, to separate out residual effects from their original signal, making the dimension of a song more intricate.

The low pass EQ can be used to get rid of buzz or hum sitting on top of a clean bass guitar line, or change a slap and tap string artifact to sound more like a purposeful tonal performance. High pass can be used to remove all upper Frequencies and hiss and noise that is recorded as part of a low Frequency signal that is not desired. It could also be used on effect tracks to change the way an effect sounds on content that otherwise has a lot of high Frequencies, but it can also be used at the highest Frequency option supplied on a low pass filter to create a special effect from a track that normally has more spectrum in the sound, like making a voice sound like it is coming from a telephone or an older recording device.

It is very rare that a pass EQ will be completely variable, meaning that it is usually provided with a few fixed Frequency options that make for a usable utility for removing trouble above or below a certain point, but this is usually not given complete flexibility. It is also not as common for there to be only a single fixed pass Frequency, since there can be different spectral issues that come up on a regular enough basis that call for using pass filtering options.

How to Mix and Master with EQ – 10 Equalizer Modes – Part Six - CDSoundMaster.com

Audio Recording with Equalizers – 10 Equalizer Modes – Part Six – 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.

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How to Mix and Master with EQ – 10 Equalizer Modes – Part Five - CDSoundMaster.com

Audio Recording with Equalizers – 10 Equalizer Modes – Part Five – Clean or Colorful EQ

This may seem like a strange choice for a topic on EQ modes. Deciding on a Mode to work with regarding EQ is a decision of how the sound is being adjusted, what affect it will have in the entire range of Frequencies, whether the slope is steep or narrow, gradual or sharp, among many other factors. The design of the EQ itself is a major factor in how the EQ reacts, and though there are many EQ's that share similar design and feature sets, the actual sonic results can be very different based solely on whether it leans more towards a clean or colorful electronic design. When these devices are emulated, their software equivalents will follow similar results.

A good example of how the electronic signal path affects how the same Mode settings are affected is the Millennia Media NSEQ-2 Twin Topology EQ. It allows the user to switch between the highest quality high voltage vacuum tube signal path or the highest quality op-amp solid state signal path that the electronics world has to offer. Using the exact same settings, the way that the Millennia Media NSEQ-2 renders the shape of the exact same setting in Solid State Mode is different than that of its identical setting in Vacuum Tube Mode. One will have a sharper result where the other will be slightly rounder. Both would be considered very precise, but that isn't the only result. Both options are extremely clean, but the subtle harmonic content that is additive, and therefore measurable, has a definite final affect on the audio signal. In my opinion, the brilliant design seems to defy gravity and logic, in that there doesn't seem to be a single setting that doesn't improve the sound. But, it always seems to add something that is pleasant sounding and beneficial to the signal, yet it is so definitively “high end” sounding that you can use it for any mastering project in any music category and never feel that there was a better option. I feel this way about a few other EQ's based on their own merits, but the NSEQ-2 definitely serves as the perfect example since it is the ideal in both solid state and vacuum tube Modes!

Cleaner EQ's may follow a minimalist signal path with few capacitors, no transformers, and minimal wiring. The GML and Sontec are the most famous and ideal versions of this type of EQ. They have plenty of settings to choose from, and they can etch out the narrow troublesome tones or smooth out an entire range of Frequencies, but they do so with very little interference to any tonal aspect of the original signal. They are very clean, but they do not lack musicality. They measure very low in distortion and the timing elements are very accurate, yet still there is something sweetening and polishing about their behavior. Even though they are designed for clarity and preciseness, even the manufacturers can describe the character as one device in their line and another as being more precise as another, or bolder in character and robust. Even in the “clean” camp there is a great deal of variety. Program Equalizers are famous for using oversized transformers, hand-crafted inductors, multiple vacuum tubes, and larger-than-life power supplies.

All of the items in their path are known to have a pleasant additive affect in the signal path, and yet they can be used on the most delicate of Program Material with absolute clarity and precision. It seems that even when there is a small measure of harmonic content and intentional heftiness in the signal chain, we can grab the subtle dynamic character of the source and somehow every detail can shine forth. Somehow, despite very low distortion, an incredibly low noise floor, precise timing elements and lack of phase shift, and an impressive flat Frequency response, we can hear the polish and silk and find it always a pleasant addition. Sometimes the benefits of clarity and color are intertwined and serve no reason or measurement for the reason they perform the way that they do.

We can remove nearly all of this character and find the most perfectly clear and clean Mode EQ in digital form, with no aliasing, no distortion, no harmonic character, and a perfect precision. For the most part, this digital EQ might be capable of matching the exact same setting as a Sontec or GML or Pultec, and it will simply not sound good. Should we use it for mastering instead of the analog choice, even if there is some chance that there is some variation of imperfection that we are unable to measure? It is my opinion that we should always rely on our ears for the final verdict, and if this leads our choices to a preference over a measurement, then we can look at character as a choice in “Clean” and “Colorful” Modes regardless of the design.

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How to Mix and Master with EQ – 10 Equalizer Modes – Part Four - CDSoundMaster.com

Audio Recording with Equalizers – 10 Equalizer Modes – Part Four – Linear Phase and Minimal Phase EQ

The usefulness and creative options of an EQ include the ability to separate how one track stands against another and blending multiple sounds together. It defines whether there is a sonic issue that needs correcting, or whether you wish to breath new life into dull source material.

We attach descriptions like “sweetening” and “silky” or “tight” and “punchy” when describing how an EQ affects the signal. When dealing with phase and EQ, considerations move beyond flexibility and layout, and into a scientific realm that some may not wish to concern themselves with. In audio, just like any other discipline, we find that the tools we choose to work with can free us, limit us, or even define our creative decisions. Therefore, we may think of a Mode as simply being determined by the shape of an EQ or the way that it is designed to handle a range of Frequencies or filtering, but Linear Phase and Minimal Phase act as Mode options for the same purposes. Minimal Phase EQ is designed to provide a high quality filtering process that is capable of sounding pure and natural while doing very little to change the timing or cohesiveness of the timing elements of the Program Material.

Phase issues can be the cause of many side effects, but it has become an increasingly small concern with professional gear. In software, phase cohesion takes the role not just of filtering and electronics, but in how sound is handled algorithmically. Therefore, the distinction between Minimal and Linear Phase can involve how an EQ handles actual processing, Gain structure, aliasing and sample rate, edge Frequency filtering, and numerous other issues. Where Minimal Phase can provide natural and precise response, it can also lead to an increase in subtle coloration to the signal the more extreme, and numerous, the filtering options employed.

With Linear Phase EQ, an extremely high fidelity process is used to keep the phase cohesion nearly perfect. The trade off can become more in favor of using less Gain and avoiding audible side effects, and in some cases, trading a bit of artistic musicality for the price of absolute unwavering and pristine timing elements. The choice to favor linearity over proven filtering options with Minimal Phase can lead to ringing and unusual overtones if extreme changes to Gain are attempted, so the choice to use Linear Phase should truly remain hand in hand with making very small, surgical and strategic changes to sound sources. With Minimal Phase, or Minimum Phase as it is sometimes referred to, we have a trade off that finds a balance between the amount of phase a filter allows for, and how well it can provide the shape, slope, and Gain desired. In order to create truly Linear Phase, it has to be possible o adjust all timing elements to the longest potential timing change, which requires a great amount of processing. But, it also places crucial elemental changes to filtering and even can affect the amount of accuracy in actual Frequency and Gain that occur. The most important affect that Phase has on the audio signal is in the sharpness and speed of higher Frequencies, or transients. It is possible for small elements of coloration to occur with any Phase from any EQ that is not purely Linear.

It is my personal opinion that an EQ that claims to be low in timing or Phase shift is generally preferable to Linear Phase, but many Mastering Engineers will disagree. I personally believe that if you listen for the changes that are made, it is much less prevalent to any overt changes in timing to use a Minimal Phase EQ in small amounts than it is to potentially change some of the slope shape and filtering and ripple effects of Linear Phase, at the benefit of near-perfect timing. Whether you are mixing or mastering, the choice of EQ can include specific features like filter type, Gain range, or Frequency settings, and now we can see how the choice of phase cohesiveness can also determine the right choice.

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How to Mix and Master with EQ – 10 Equalizer Modes – Part Three - CDSoundMaster.com

Audio Recording with Equalizers – 10 Equalizer Modes – Part Three – Fixed versus Variable Frequency Modes

When analyzing the difference between Fixed and Variable EQ Frequencies, we once again visit the importance in the design and construction of the analog EQ and its purpose. Fixed Frequencies are common in classic Program Equalizers and in Console EQ's. Although they can be the option of any EQ design, these are the most commonly found in these categories, because they were designed with a specific purpose to focus on specific Frequencies that are the most commonly needed for specific individual vocals and instruments.

The filtering process is specifically chosen in the design of the EQ and can help the user work in a consistent and intentional manner that can define their creative signature, but some find deliberate, predetermined limiting and prefer freely adjustable Frequency selection, as is most commonly found in Mastering EQ's. Variable Frequency Modes can not only provide the ability to get more specific and surgical in our tracking, mixing and mastering processes, but it can also be used dynamically as a song effect. Control and automation of changes in Frequency moves can become a musical element in composition, sound design, and mixdowns that cross the boundary of the art of mixing into the art of actual song creation. This brings EQ into a new category, not just for an engineer's task of tracking, mixing, or mastering, but also at the writing stage.

Using EQ as a filter to change the smooth transition of musical content to swell or pass from one Frequency to the next in smooth transition can act like a sonic ocean wave sweeping by, telling our ears that sound is gliding upwards or downwards, creating an actual musical response instead of making corrective changes.

This determining factor draws a strong line between Fixed and Variable Frequencies, showing how there is more to EQ than just quality and preferred uses. Now, we see that creative choices can cross the barrier between utility into the actual writing of music. Next, lets take a look at Linear Phase and Minimal Phase EQ's.

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