A simple approach to mixing a rock song: Part 4 - Equalization (What is it?)

Submitted by mic on Fri, 03/23/2018 - 13:14

admin: First posted on 2007 06 28

Panning is one way to separate clashing instruments. Equalizing is another. Equalization changes the amplitude of various frequencies in the sound mix. Some people even swear that equalization creates the perception of moving instruments up and down in the mix (as opposed to panning, which moves them left and right). Is that even possible? Perhaps. Having different instruments occupy different frequency ranges definitely makes them more distinct in the mix.

Notes, frequencies, and frequency ranges of instruments

Before we start moving instruments up and down, let's figure out where instruments are. Let us call C4 the middle C of the piano. This C may carry one frequency or another depending on tuning (the type of tuning, how well the instrument is tuned, etc.). For the sake of this example let us say that this C is the frequency of 262 Hz. Going up from C4 we could look at E4 (say 330 Hz), A4 (440 Hz), C5 (523 Hz) and so on. We can go as far up as C8 (say 4200 Hz) and as far down as C0 (16 Hz).

It should then be easy to infer frequency ranges for most instruments. The electric and acoustic guitar should be between 80 Hz and 880 KHz. The bass guitar is around 40 Hz to 300 Hz, and so on. Vocals can go anywhere from 90 Hz to 1.2 KHz. Drums are complex because the sound produced by a drum can have so many pieces, but for the sake of the argument, let’s say that the kick drum is around 60-80 Hz, the snare is around 240-250 Hz, hihats and cymbals are over 6 KHz, toms show up at 240-250 Hz and floor toms are around 120-130 Hz. You should already know that the piano is very versatile, and ends up anywhere between 16 Hz and 5 KHz.

This information is somewhat correct, but:

  1. Instruments rarely play in their full ranges. Тhe piano can cover a wide range but usually does not. The piano piece could play, for example, in the range of the electric guitar. Vocals are similar. Bass vocals are between 90 Hz and 350 Hz (opera requirements are more precise; bass vocals should be from F2 to F4, but I have rounded those numbers). Baritone vocals range between 100 Hz and 390 Hz. Tenors are between 130 Hz and 490 Hz. Altos go up to 700 Hz and sopranos cover anywhere from 250 Hz to 1.2 KHz;
  2. Instruments generally have undertones and overtones. The ranges show the notes that instruments play, but all these notes will be accompanied by other frequencies. For example, toms will produce overtones over 8 KHz. These are usually hard to distinguish as separate sounds, but people do notice a difference between different instruments that produce the same pitch but with different quality. Brass instruments, for example, produce very notable overtones, which define their brassy sound. I have heard that the non-even harmonics of the sax, for example, is what makes the sax generally annoying. The even harmonics of the tube amp is supposedly what makes the tube amp warmer. That may or may not be true. I have seen comments in some literature that non-harmonic overtones are what makes the sound unpleasant; and
  3. Instruments produce a variety of sounds during the playing of a single note. A drum, for example, has its general drum sound, but begins with a slap. Even though the kick and the snare are at 60-80 Hz and 240-250 Hz as above, the initial slap of the drum is between 2 KHz and 3 KHz. While vocals rarely have obvious overtones, they do have sibilance (the "s" sounds) that could be between 6 KHz and 10 KHz. Vocal presence, on the other hand, is controlled by frequencies around 5 KHz. The cymbals are very complex, as they have an initial slap between 2 and 4 KHz, sibilance from 6 to 10 KHz and a shimmer above 8 KHz. Even more interesting is the sound of the pick on the guitar strings, or the "scratch" produced by the guitarist’s fingers, which have their own frequency ranges above 6 KHz.

A couple of additional facts: Overtones define a lot of the timbre of an instrument. Even though two instruments could play in the same pitch, they have perceivably different qualities. These qualities are the instrument’s timbre. One special type of overtones, which are also greatly responsible for timbre, is called formants. Formants are frequencies (one or more) that are produced by an instrument independently of what the instrument is currently playing. These are especially true for wind instruments and vocals. The flute, for example, is said to have a formant at 800 Hz.


The most important things to remember about equalization are as follows.

  1. Equalizing does not change the frequency of an instrument. If it did so, it would be changing what the instrument is actually playing (i.e., it would be doing "pitch shifting"). The frequencies that already exist will continue to be there (perhaps at different amplitude) and the frequencies that do not exist will not be created. You cannot use an equalizer to create a frequency that does not exist;
  2. Almost any sound is composed by a multitude of frequencies and is therefore very complex; and
  3. Equalizing changes the predominance of some frequencies in the mix. When you equalize you would change the timbre of an instrument, which means that you can diminish some of the qualities that you do not like, or you can boost qualities that you like.

In summary

Notes have their own frequencies. Notes do not have strictly specified frequencies. Everything depends on tuning. Even though with different tuning the same note can have a different frequency, with contemporary conventions the new frequency is usually not that far from the first. We can say that notes have well defined approximate frequencies. Middle "C" (or “C4” as above) is around 262 Hz. "A" in the same octave (A4) is around 440.0 Hz. Here is a table with the frequencies of notes in Microsoft Excel.

Instruments play in fundamental ranges. If notes have specific frequencies, the notes that instruments can play determine their fundamental frequency ranges. If a bass goes from E1 to D4, for example, then the bass is between 41 Hz and 294 Hz (check out our table of instrument frequency ranges.

Instruments produce overtones and undertones and have formants. Instruments produce sounds with other frequencies in addition to the frequencies in their fundamental ranges above. Overtones and formats define the timbre, or inherent quality of the instrument.

Equalization changes timbre. I hope you have figured out by now that equalizing in the instruments frequency ranges is probably the least important thing you can do. Equalizing to control overtones and undertones is probably more interesting.

Equalization could remove unwanted sound components. You could attempt to reduce sibilance, or to boost the initial slap of the kick drum. One thing you cannot do, however, is introduce "wanted" sound components that do not already exist.

Why use equalizers?

Here are the good reasons to use equalizers.

  1. Remove undesired sound components, such as sibilance;
  2. Change the qualities of a single instrument to make it sound better – introduce crispness, introduce presence, boost bottom end;
  3. Change the qualities of an instrument to move it away from another instrument in the mix, so that the two do not clash. An electric guitar and a vocal could, in principle, be very similar in timbre. Equalization could change that; and
  4. Change the qualities of the whole song – introduce some shimmer to open up the song, and others.

authors: mic

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