"He Wears Black and Has a Beard"

Feel and Intuition: EQ without numbers

Toby Roworth

Feb 11, 2013

One of my pet hates is when someone explains to me something like "vocals sound best with a slight boost at 3k and a cut at 220 to remove that nasalness". I refer to this as "EQ by numbers".
When it comes to EQing I prefer a more organic approach, based not on magic numbers but, like everything in sound, what I can hear. This allows adjustment for conditions on the night, continual trial & improvement and a little creativity.
The introduction stops there - I planned a rant, but then thought better of it (this guide's long enough as it is).

Toby's Guide To EQing

Golden Rules

Filter types

EQ, electronically is a "filter" circuit combined with an amplifier. A filter allows certain frequencies to pass whilst blocking others, and is usually build with resistors, capacitors and, in posh ones, inductors. The amplifier is a simple op-amp, set up to give both positive and negative gain (boost and cut). The electronics are quite a lot more complicated than this in practice (as I've found whilst trying to create one myself for a guitar pedal), but that's for a future post.
Filters have two important characteristics: corner frequency and rolloff. Corner frequency is the frequency you care about - where the filter begins/stops acting (except in a bandpass - see below) - and id measured in hertz (Hz). Rolloff is how quickly the signal gets attenuated outside the filter, and is measured in decibels per octave (dB/octave) - they're usually 6, as this is easy to make. This means that every time the frequency doubles/halves (check your music/physics and you'll find that's what an octave is) there will be a 6dB difference, perceived as half the volume.
For now, there are three types of filter:

Low-pass filter

Lets low frequencies below the cutoff frequency pass, whilst higher frequencies get attenuated by the rolloff. A type of shelving filter, these are normally used for the Lf part of an EQ.

High-pass filter

Lets high frequencies above the cutoff frequency pass, with frequencies below getting attenuated by the rolloff. Another type of shelving filter, these are often used for the Hf part of an EQ.

Bandpass filter

Effectively a combination of the above, a bandpass filter lets a band of frequencies pass, centered around the cutoff frequency. These are usually implemented as a low-pass and high-pass filter, and used for the mid bands of EQ. They could also be used for Hf and Lf, but I don't think that's too common.
A very narrow bandpass is known as a notch filter, and has a much higher rolloff which can be dozens of dB/octave.

How to simply EQ a single channel with a range of EQs

The Humble Two-band EQ

Identified by a mere two knobs, usually called Hf and Lf, or worse treble and bass, EQing with a 2-band EQ is simple:
  1. Buy a new sound desk
  2. Follow the appropriate guide below
Seriously consider it - no sweepable bands leaves you very limited, and you have no control over what happens in the mid.

The Rubbish 3-band EQ

3 knobs, 3 frequency bands. Don't look up what frequencies they act on - it'll just give you those snobby numbers I don't like.
Bear in mind that without a sweepable mid, you're missing out in most of the fun.

The Useful Three-Band EQ

This has four knobs, usually with one in a different colour, or at least with a scale measured in Hz, not dB. The sweepable mid allows you to select which frequencies the mid cut/boost acts most at (the corner frequency), so you begin to have a say over how your EQ works.

The Wonderful Four-band EQ

Seen on most desks costing over a few hundred, or with more than 16 channels, this EQ has 6 knobs, usually in this order: The frequency knobs will normally be in a different colour.
Having two sweepable bands to play with gives you a lot of flexibility, and is one of the features that make spending a lot on the mixer worthwhile.

The Showoff [4]-band

Usually only found on digital desks, you get gain and frequency adjustment on all four bands, along with a "Q" knob. The Q knob adjusts how narrow the frequency band you're adjusting is, allowing you to remove a narrow notch where feedback is bad or boost all the mid ever. You might also be able to change the Hf and Lf from shelving filters to bandpasses.

The Overkill Graphic

A graphic is great, but overkill for a single channel in most cases. They break the entire audible spectrum into narrow bands which can be boosted and cut. They also fall out if the scope if this guide.

Setting a Non-sweepable Band

  1. Define better
  2. Turn the knob up to about 3 O'clock and listen
  3. Turn it down to 9 O'clock and listen
  4. Turn it in the direction it sounded better until it sounds best
  5. Listen, and decide if the channel sounds better overall. If not go back to step 2 or, optionally, step 1.

Setting a Sweepable Band

  1. Define better and worse
  2. Turn the boost/cut knob to about 3 O'clock
  3. Sweep the frequency knob from it's lowest to highest setting, slowly, whilst listening for "better" and "worse"
  4. Sweep it again, and stop at the point where it sounds either best or worst.
  5. Turn the boost/cut knob up if it sounded good, or down if it sounded bad
  6. Keep turning until it stops making a difference/starts causing other problems, and then turn it back just a touch
  7. Listen, and decide if the channel sounds better overall. If not go back to step 2 or, optionally, step 1.

Notes on EQing a Whole Channel

  1. Try to make the channel slightly louder in the front of house (FOH) mix, so you can hear what your changing
  2. Don't EQ through headphones - you need to hear how your changes actually sound to the crown through the PA and the rooms acoustics - £300 headphones don't replicate this very accurately!
  3. If the channel has a button to switch the EQ in/out, try it, and check it actually sounds better
  4. It's generally easier to do the Hf and Lf before the mids, as these can have a good effect without much effort, leaving the mids for more precise adjustment

EQing a Whole Desk

EQing a single channel isn't too hard. EQing a whole desk gets more complicated. There are a couple of Toby-approved methods for doing this well and, by blending then together, very good results can be obtained.

Frequency Distribution

Parts are easier to tell apart when they are perceived at different frequencies. By minimising overlap, it can be much easier to hear everything. Some tips:

Subtractive Mixing

This is borrowed off someone, but I don't know who, and have rewritten it from scratch. It's a useful technique for noisy environments, or those conducive to feedback

A Final Note on Numbers

Mentioning numbers is fine - there are times where a frequency needs to be communicated, and us sound guys don't really do "High C". But don't let the numbers dictate what you do - let the sound guide you instead.