Demystifying Music Technology: The Equalizer

Demystifying Music Technology: The Equalizer

Our resident tech guru Christopher Steller is back, this month to talk about the equalizer - fondly known as EQ to people who know what it does. 

Christopher Steller
Melbourne, Australia

Demystifying Music Technology: The Equalizer

Our resident tech guru Christopher Steller is back, this month to talk about the equalizer - fondly known as EQ to people who know what it does. 

Denzel Washington will not be making an appearance in this episode, and there will be no reference to using power tools as projectile weapons. My final part of explanation for the mixer channel strip will cover the section known as equalisation or the ’EQ’.

Home music systems often contain the ability to alter the tone of your music with treble and bass adjustment controls, which give a general increase or decrease in these areas of the sound (known as shelf EQ). In our DAW mixer channel the EQ is a lot more precise, using a device called a parametric EQ. You have the ability to select a frequency to control, decide how much of a chunk around the selected frequency you wish to change, and then decide whether you want to increase or decrease this frequency. The three parameters available in this process are frequency selection (kilohertz or kHz), gain (decibels or dB) and width (or Q).

One important thing to remember is that EQ is not just used to increase a tone or frequency of a sound - it can be used to remove unwanted clicks or squeaks, smooth out screechy instruments or vocals, or help blend two instruments that have very similar tonal characteristics (by removing some of those characteristics from one instrument so the other can stand out).

Within a DAW you are at an advantage over a traditional hardware mixer because you can have as many virtual equalisers as you want, and from an old school point-of-view the Reason channel strip in my previous article is perfect for the long-time user.

The EQ section of the more traditional looking Reason channel strip contains 4 bands or 4 different frequencies that can be altered in your sound: HF for High Frequency, HMF for High Mid Frequency, LMF for Low Mid, and LF for Low Frequency. To hear the effect of the EQ we’ll use the HMF: by increasing the gain of the dB knob by a small amount and then turning the kHz knob up and down, you will hear the results of adding gain at selected frequencies. By turning the dB control anti-clockwise, you will be decreasing the gain of the selected frequency - sweeping with the kHz knob now will result in a removal of tone at the selected frequency.

When you are working within Apple’s Logic, the Channel EQ plug-in gives you a visual representation of how it affects your audio across the frequency spectrum, which is great for professionals and first-timers.

If you have an audio track of an individual instrument or voice that you can experiment with in Logic, add the Channel EQ to the track and open it while the track is playing. When you move your mouse over the plug-in you will notice there are several colour-coded bands of EQ, so you have a lot of control here. Move over the horizontal line and you will see coloured circles appear - click and drag the circle near the 1k (kilohertz) point and move it around. You will notice the numerical settings for that point (which are also colour-coded) changing as you move: visual and numerical feedback, simultaneously, is a good thing. Now it’s critical listening time: drag the circle around slowly to hear what is happening - if you increase or decrease the gain of a frequency (vertical movement) you will hear a change in the tone of the track, and then by sweeping the circle left and right (horizontal movement) and listening carefully you can pinpoint highlights in the sound of the instrument.  NOTE: at this point you can understand the importance of a good audio system to listen to your work - you need to hear the details of your editing.

In terms of the frequency bands of the Channel EQ plug-in, the four middle bands are parametric (as described earlier), the two outer bands are shelf EQ, affecting broader areas of the upper and lower sound, and the furthest left and right bands are filters (we won't worry about these now).

If you want your cellos to have a bit more bass, you can increase the low end of the recording with EQ. If you record a piano that has a squeaky sustain pedal, it is possible to soften the squeak by finding and decreasing that frequency area, but at the cost of anything else that occurs at the same frequency.

In studio terms, here are some ideas for enhancing a particular quality in an instrument:

  • Bass drum – bottom 50-120hz / boxiness 400hz / basketball sound 1khz / attack 2.5khz
  • Snare – fatness 100-240hz / boing 900-1khz / attack 5khz / snap 10khz
  • Rack toms – bottom 200-540hz / Ring 900hz / attack 5khz
  • Floor toms – bottom 90-120hz / attack 3-5khz
  • Cymbals – clang 200hz / crispness 7-10khz
  • Electric guitar – fullness 240-500hz / bite 2.5khz / edge 4khz
  • Acoustic guitar – fullness 80-120hz / body 240hz / presence 2.5-5khz
  • Piano – fullness 80hz / body 240hz / honky tonk 2.5khz / presence 5khz
  • Bass guitar – bottom at 60-100hz / string sound 700hz / snap 2.5khz-3khz
  • Vocals – Fullness 120hz / boominess 240hz / presence 5khz / air 10-15khz
  • Organ – Fullness 80hz / body 240hz / Presence 2-5khz
  • Horns – Fullness 120-240hz / piercing 5khz
  • Strings – Fullness 240hz / Scratchiness 7-10khz
  • Conga – Bottom 100-160hz / ring 200hz / slap 5khz