subtractive equalization

Don’t boost – reduce! Subtractive equalization and your home studio mix

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Our friends at Cakewalk offer these recording tips focused on mixing, EQ, and the concept of carving out frequencies to improve your audio mix

This recording tips post originally appeared on Cakewalk’s blog. Reprinted with permission.

Equalization is one of the most powerful tools an audio engineer can get their hands on. Live engineers, post-production engineers, and recording engineers all have their specific uses for it. It’s so powerful, some beginners and home studio users habitually reach for it without understanding what it can ultimately do to a mix.

Before we discuss equalization, let’s consider the concept of volume. It is in our human nature to enjoy music at high volume levels. To most, increasing volume directly correlates to better sound. In an audio mix setting, dramatically boosting various frequencies can be a crutch for an inexperienced audio engineer. But by increasing the gain of a specific frequency band on an EQ, you can subsequently add unwanted gain to the overall mix. Typically the problem that follows is a battle to keep your master fader from clipping, and you are suddenly stuck in a gain staging paradox. This can happen to best of us.

One way to avoid this gain staging dilemma is to apply subtractive equalization techniques to the elements of your mix. Instead of boosting your favorite signals, try limiting yourself to cutting. We can call this concept “carving.” Let’s take a look at a musical example that will demonstrate this technique in a typical rock mix.

Recording tips for EQing the snare drum
Generally, the snare is the focal point of a typical rock oriented audio mix. I’ve started with all my faders down and raised the snare to a suitable level: 0dBu. This recording was tracked with two snare microphones. The bottom snare microphone captured the sizzle of the snare and the top microphone captured much of the attack.

The first issue I noticed when isolating the snare recordings was the amount of kick drum and cymbal that were captured. The drums were recorded in a small room with minor acoustic treatment, so the initial reflections from behind the drum kit and off the low ceilings and neighboring walls caused more bleed into the snare microphones than I wanted. To remedy this, I began by attenuating the lower frequencies on both the top and bottom snare microphones to filter out any bleed from the kick drum. The snare top microphone’s high pass filter was applied at 78Hz, and the snare bottom microphone’s Low Shelving EQ band was set to 101Hz. This does not isolate the sound of the snare from the kick, but rather strips the snare signals of those low end characteristics. These characteristics become more present during the mastering process so it is important to carve out the sound now.

After that, some filtering was applied at the top end of both tracks to reduce some splash from the cymbals. The snare top microphone’s low pass filter tapered off at 12.7kHz, while the snare bottom microphone’s low pass filter was applied a bit higher, around 14.9kHz. Targeting a problematic frequency might require you to listen with your eyes closed. Many of us are guilty of listening with our eyes rather than actually looking away from the computer monitor and focusing in on the sound. In my opinion these filter cuts start right where the sound of the snare begins to suffer and the cymbals do not become too obviously filtered from the signal.

I applied a massive cut at 313Hz on the snare top signal and another on the snare bottom around 357Hz. There is an attractive thick response between 78Hz and 313Hz and again between 101Hz and 357Hz. By cutting, I have effectively exposed that thick response instead of boosting that entire spectrum. In addition, I felt that the snare bottom signal resonates nicely around some of the sibilant frequencies as well as the high mid range. To reinforce those frequencies, I scooped -3dB of gain at 2kHz to enforce the frequencies in the 5 – 6kHz and 400Hz – 1.5kHz range.

Check out the sound clips, and see Fig 1 for EQ settings.

subtractive equalization
Fig 1 – Snare Top (Left), Snare Bottom (Right)


EQing the guitars
You can change the guitar tone significantly by carving out the correct frequencies and reducing those that introduce unwanted noise. Distorted electric guitars tend to occupy most of the mid-range based on the nature of their sound. This mix was tricky because the band is instrumental and their music relies heavily on the layering of multiple guitar tones.

Here I have chosen to attenuate the unwanted rumbling of the of the low end of the rhythm guitars using the supplied high pass filter. The bass guitar is rather guitar-like in this song, therefore it is important to make room for that. The high pass filter for Guitar 1 was applied at 50Hz and similarly to Guitar 2 at 47Hz. Why not the exact same frequency you ask? Having the slightest bit of inconsistencies between two identical hard panned performances tends to create the illusion of more separation than there actually is. In this example the outcome is subtle.

subtractive equalization
Fig 2 – Rhythm guitars

Once that was done, I scooped the mid range around 800Hz on Guitar 1 and around 515Hz on Guitar 2 to attenuate the nasal midrange frequencies. This also reveals the frequencies in the low midrange that guitars never cease to benefit from. Afterwards, I felt the need for the slightest bit of high end on these rhythm tracks so I gently cut around 2.2kHz on Guitar 1 and a bit more at 7.9kHz on Guitar 2. This pushes our ears to listen for the frequencies that occupy the space around these areas.

The lead guitars needed more clarity than they did anything else. Since this is an instrumental, I thought it only fitting to treat these main melody instruments as the “vocal” track. The clarity I wanted occupied the sibilant realm, so I filtered down to the top of this spectrum leaving the slightest inconsistencies to make room for the cymbals. Also, both tracks required a dip in the low to midrange at 167Hz and 234Hz to reduce any muddy tones that snuck in from time to time throughout the song.

subtractive equalization
Fig 3 – Lead guitars


EQing the kick drum
If the snare is the primary listening point for rock music, then the kick drum is the second most important. By working in the guitars in over the snare, I was met with the challenge of working in a solid kick drum sound. This kick drum was tracked using two different kick drum microphones, one deeper into the drum than the other. For reference, the first kick signal is called the “kick-in” microphone and the second is the “kick-out” signal. (This is one example of the nomenclature used by many engineers to differentiate between the different microphones placed on a drum set)

I started by blending the two signals to my liking and then attenuating any unwanted rumbling around 79Hz. I also reduced most of the high end of the kick-in signal. The low pass filter was applied drastically at 927Hz. In tapering off the high end, I can reduce the unwanted sound of the cymbal splashing and use the kick-in microphone for the proper thump that I was looking for.

subtractive equalization
Caption: Fig 4 – Kick drum

The kick-out microphone had a much smoother tone, so I used this to capture the slapping of the beater against the drum. This slapping of the beater is what will cut through on a pair inexpensive speakers that do not have much bass response, which is important to think about while shaping your sound. Lastly, using my ears, I sought it fitting to attenuate around 552Hz and 7.7kHz. If you are familiar with heavy rock or metal, then you can understand that the kick needs to have a present and simultaneously thick tone to it. This tone is mostly achieved by reducing the mid-range and shaping the low and high end to your liking.

The kick drum is a tough instrument to work into a mix because it does not follow the same rules as other instruments. The trick is getting the kick drum presence into the mix without actually overpowering the mix, which is why it is important to attenuate the kick drum’s frequencies rather than boost them.


EQing the bass guitar
The bass in this track caters to fans of the early Metallica era. Bassist Cliff Burton popularized this distorted sound on such tracks as “(Anesthesia) Pulling Teeth.” It’s important to blend this type of bass tone into the bottom of the guitars. In this mix, the guitars and bass become a single unit ebbing and flowing together at certain points through the song.

We can assume that there was a lot of processing done to this track before its transfer into SONAR. It’s important to capture the sound before you start mixing so that your mixing process is not a patch-job.

This tone is aggressive and piercing to the ear, and the aural fatigue you may experience while soloing this track and listening to it rather loudly for more than 10 seconds is an indication that this instrument track needs attention. I aimed to adjust the bass track to fit like a glove under the mix by applying a high pass filter at 78Hz with a steep bandwidth setting. The amount of bass here needs control. Using a compressor to control the sound would be redundant because of how much overdrive was applied to this track. The overdrive has ultimately eliminated any trace of strong transients.

Lastly, there is another dip in the EQ around 2.2kHz. This adjustment reduces some of the aforementioned piercing sound. Any harsh tones in this register will be too overbearing in the mix.

subtractive equalization
Fig 5 – Bass guitar


EQing the drum kit
The rest of the drum kit was adjusted as follows.

Tom 1: HPF at 56Hz, -10dB of gain at 596Hz

Tom 2: HPF at 45Hz

Tom 3: HPF at 49Hz, -10.3dB at 317Hz, and -8.2dB at 1.6kHz

High Hat: No processing done, just blending

Overheads:
1) HPF at 113Hz, -10.6dB at 942Hz
2) HPF at 88Hz, -8.8dB at 2.1Hz

Tom tom recording tips
Fig 6 – Tom toms
Recording tips for overhead mics
Overheads 1 and 2

When should you boost EQ frequencies?
Boosting is something that you can do anytime you want with any given instrument. Obviously it is your own choice, but if you find yourself constantly pulling your faders up and down because your master level is clipping then you may want to apply these EQ techniques to your workflow.

Mixing is as much of an art as it is the science of understanding the logical ways that instruments interact with one another. By introducing this (hopefully) logical method of subtractive equalization, hopefully you have another technique to employ the next time you approach a mix.




Hear more at Truthseeker’s BandCamp site.

Cakewalk is the leading developer of powerful and thoughtfully designed products for the modern musician. These products include award-winning digital audio workstations and innovative virtual instruments. Millions of musicians worldwide – including Grammy® and Emmy®-winning producers, composers, sound designers, and engineers – use Cakewalk products daily to produce audio for the professional music, film, broadcast, and video game industries. The Cakewalk blog offers technical tips, tutorials, and news relating to their products and audio recording.

Screenshot images in this post show SONAR X3 Producer. Download the Free Trial of SONAR X2 Producer or learn more about Mixing in SONAR.

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10 thoughts on “Don’t boost – reduce! Subtractive equalization and your home studio mix

  1. Good article that will help me to enforce this issue when trying to explain it to other band members who have less knowledge about recording process. Simple and to the point.

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