Learning what different frequencies sound like and the effect they have on the sound of different instruments is an invaluable skill. These are the names we use to classify the bands – the frequencies are approximate, so use your ears!
> 20 – 60 Hz – Sub-Bass: Gives boom, depth, and richness – too much sounds flabby and out of control. Small speakers don’t reproduce this.
> 60 – 150 Hz – Bass: ‘Thump’ and punch in drums, especially kick and snare, and richness in bass and guitars. Too much sounds woolly.
> 150 – 1 kHz – Lower mid: Important for warmth, but too much sounds thick and congested. The 500 Hz – 1 kHz region especially is crucial for a natural vocal tone, but too much sounds boxy and nasal.
> 1 – 3 kHz – Upper mid: The most sensitive area of the ear, important for edge, clarity and bite, but too much will sound harsh and tinny.
> 3 – 8 kHz – Low Top: Provides fizz and sizzle; and edge and aggression in guitars – too much sounds thin and brittle.
> 8 – 12 kHz – Top: Gives openness, air and clarity – too much sounds over-bright and glassy.
> 12 – 18 kHz – Very high top: These frequencies can add sheen and sparkle and sweeten things up, but too much sounds unnatural, gritty and forced. [FYI – I have the Kush Clariphonic parallel EQ hardware. I add these frequencies on my mixbuss or sometimes use it for vocals. It really opens up that top end. A little goes a long way.]
Tip #1: Don’t solo an instrument when EQ’ing. Set the EQ when playing the instrument in context with the rest of the track. You can solo to quickly check things, but be sure to take out of solo mode fairly quick.
Tip #2: Sometimes when soloing a track or instrument, the EQ we add makes that instrument sound worse! But in context of the whole mix it sounds great. That is what matters. Part of the time you can expect this to happen.
Tip #3: If there are two parts that are fighting in the mix because they occupy the same frequency range, it can sometimes help to boost the EQ on one of them and cut the other at the same frequency, then reverse the strategy and boost the second sound in a different place while cutting the first. This emphasizes the contrast between the two parts, with gentler boosts, and helps stop things sounding unnatural.
Tip #4: In regard to Tip #3 above, this can sometimes be called ‘masking.’ Masking is when two instruments are fighting for the same frequency or frequency space. For example, kick and bass guitar. If when the kick hits, the bass is obscured some, this is masking. Using Tip #3 above will help get rid of this problem. Make sure to ‘cross-EQ’ both ways. In other words, boost instrument 1 and cut instrument 2 in same place. Then boost instrument 2 and cut instrument 1 in same place.
Tip #5: Do a ‘boost & sweep.’ When searching for a frequency that you want to get rid of, use a bell curve EQ (band, or parametric), boost @12 dB with a somewhat narrow bandwidth (high Q). Sweep up and down in frequency until you find (hear) the unwanted or annoying frequency. Then set that band for a cut instead of a boost. How much you cut depends on the specific situation, it might be a little or a lot.
Today I am going to talk about the Q parameter on the bands of an EQ. We will be going a little deeper than we normally do, but that’s the nature of the Q factor.
The Q setting is going to affect the bandwidth of an EQ band. This means how much or how little of the frequencies will be affected with a boost or a cut. [Q stands for Quality factor]
On a basic level, one can see that when changing the Q setting, the bandwidth either gets wider or more narrow. Why does it do this, what does that affect, and how do I know which setting to use? Keep reading.
1 kHz bell curve boost
This typical view (above) is often referred to as a ‘bell’ curve due to the upper portion’s resemblance to the shape of a bell. In regard to the bell curve above, it has a center frequency of 1 kHz and a boost of 12 dB. (The solid line represents a boost; the dashed line shows if it were a cut).
The Q parameter controls the shape of the EQ curve. High Q values use steeper curves, which affect a smaller range and allow you to pinpoint specific frequencies. Low Q values affect a wider range of frequencies and tend to sound more gentle when used subtly. Q is the ratio of center frequency to bandwidth, and if the center frequency is fixed, then bandwidth is inversely proportional to Q—meaning that as you raise the Q, you narrow the bandwidth, and when you lower the Q, you widen the bandwidth. Q is by far the most useful tool an EQ offers, allowing you to attenuate or boost a very narrow or wide range of frequencies within each EQ band. (More on bandwidth below)
When using EQs, we are concerned with how much of the bandwidth we are affecting. We do this in octaves. When dealing with frequencies (Hertz), a doubling of the number is raising one octave higher. Conversely, halving the number is lowering one octave. Middle C (on a piano) is roughly 262 Hz. Going up one octave higher, to the next C up on the piano, the frequency is twice that, or 524 Hz. Going to the C below middle C is 131 Hz.
In order to understand Q, we have to focus on two other details. The center frequency (the one we choose for the band, i.e. 1,000 Hz), also known as f0 , and the bandwidth (f2 – f1).
Looking at the graph below, we see a boost of 12 dB. But we measure the bandwidth 3 dB down from 12 dB, which is 9 dB. The width of this, measured in octaves, is what the Q sets. In our example above, if the center frequency is 1 kHz, we can set the Q to affect one octave, centered around 1 kHz. Or, 2 octaves, 1/2 octave, 1/3 octave, etc. [Remember, the bandwidth is always measured at 3 dB down from center frequency]
Fig. 2
Q is defined as: Q = center frequency ÷ bandwidth
For example, a filter centered at 1000 Hz that is 1/3-octave wide has frequencies located at 891 Hz and 1123 Hz respectively, yielding a bandwidth of 232 Hz. Q, therefore, is 1000 Hz divided by 232 Hz, or 4.31. (Again, remember, this is 3 dB down from center frequency).
If you want to do a quick estimate of bandwidth, take the inverse of the Q number. A Q of 1 will refer to a one-octave bandwidth; a Q of 4 will be 1/4 octave; a Q of 2 will be 1/2 octave; a Q of 10 will be 1/10 of an octave. A Q of .25 would indicate a four-octave bandwidth. This will not give you a precise bandwidth, but will be close. The math behind these shortcuts is complicated. It’s a relatively complex multi-step algebraic formula that ties Q and the bandwidth together.
We can always refer to a table or chart for more precise numbers. The following table shows the frequencies of a Q setting for one-octave bandwidth (a Q setting of 1). Listed is the center frequency (which we set), along with the upper and lower frequency, for a one octave bandwidth.
Octave Bands
Lower Band Limit (Hz)
Center Frequency
Upper Band Limit (Hz)
11
16
22
22
31.5
44
44
63
88
88
125
177
177
250
355
355
500
710
710
1,000
1420
1420
2,000
2840
2840
4,000
5680
5680
8,000
11360
11360
16,000
22720
Q settings and their associated bandwidth (BW) in octaves.
Conversion chart or table ‘bandwidth in octaves’ to quality factor Q
BW inoctaves
Filter Q
BW inoctaves
Filter Q
BW inoctaves
Filter Q
BW inoctaves
Filter Q
1/80
115.4
1
1.41
4
0.267
7
0.089
1/60
86.6
1 1/4
1.12
4 1/4
0.242
7 1/4
0.082
1/50
72.1
1 1/3
1.04
4 1/3
0.234
7 1/3
0.079
1/40
57.7
1 1/2
0.92
4 1/2
0.220
7 1/2
0.075
1/30
43.3
1 2/3
0.82
4 2/3
0.207
7 2/3
0.071
1/25
36.1
1 3/4
0.78
4 3/4
0.200
7 3/4
0.068
1/20
28.9
2
0.67
5
0.182
8
0.063
1/16
23.1
2 1/4
0.58
5 1/4
0.166
8 1/4
0.058
1/12
17.3
2 1/3
0.56
5 1/3
0.161
8 1/3
0.056
1/10
14.4
2 1/2
0.51
5 1/2
0.152
8 1/2
0.053
1/8
11.5
2 2/3
0.47
5 2/3
0.143
8 2/3
0.050
1/6
8.65
2 3/4
0.45
5 3/4
0.139
8 3/4
0.048
1/5
7.20
3
0.40
6
0.127
9
0.044
1/4
5.76
3 1/4
0.36
6 1/4
0.116
9 1/4
0.041
1/3
4.32
3 1/3
0.35
6 1/3
0.113
9 1/3
0.039
1/2
2.87
3 1/2
0.33
6 1/2
0.106
9 1/2
0.037
2/3
2.14
3 2/3
0.30
6 2/3
0.100
9 2/3
0.035
3/4
1.90
3 3/4
0.29
6 3/4
0.097
9 3/4
0.034
10
0.031
Here is yet another chart for select octave bandwidths.
Q factor as a function of the bandwidth in octaves
Bandwidth inoctaves
FilterQ factor
3.0 wide
0.404 low
2.0
0.667
1.5
0.920
1.0
1.414
2/3
2.145
1/2
2.871
1/3
4.318
1/6
8.651
1/12 small
17.310 high
Below are some pictures using fabfilter’s Pro-Q with different Q settings. Sometimes pictures explain things easier. Hopefully this will show what I’ve tried to explain with words and calculations.
Memorizing all of the numbers above is a bit of a task. Here is a way to calculate these Q’s simply. It’s certainly not perfect, but it does offer a way to find these Q’s quickly.
By multiplying the number 2.05 with the first Q setting, .667 (2 octave bandwidth), you get 1.37. When rounded up, this equates to 1.4 – a number very similar to the Q setting for 1 octave.
If you continue multiplying 2.05 by each number that comes after, you’ll be able to equate Q’s that are very closely related to the exact numbers above.
For example: 1.37 x 2.05 = 2.8 or roughly a 1/2 octave bandwidth
2.8 x 2.05 = 5.75 or roughly a 1/4 octave bandwidth
The numbers certainly aren’t exact, but they get you close enough to a workable number, all while having you memorize only 2 numbers – .667 and 2.05.
Personally, I don’t like this because to get to a 1/4 octave, you have to run the calculation 4 times. But if this works for you – go for it!
Conclusion:
Practically speaking, setting your Q and it’s bandwidth to an octave or an octave based setting, drastically increases the musicality of your mix. On wider settings it makes it sound more natural and musical, on narrow settings it allows you to know the notes that you are affecting.
Consider using these shortcuts and octave based equalization whenever you want a quick, and accurate way to affect your mix.
I hope you were able to hang in there for this whole discussion. If you got lost in any of this, continue to hit it again and again until you fully understand it. I had to. Go down the rabbit hole and chase this until you “get it!”
If you look toward the bottom of the EQ pictured above, you will notice 5 different bands: 1. LF, low frequency, red; 2. LMF, low-mid frequency, orange; 3. MF, mid frequency, yellow; 4. HMF, high-mid frequency, green; 5. HF, high frequency, blue.
In today’s blog I will talk about these five bands. I want to start with band 1 and 5. These are typically used and referred to as “shelves.” Band 1, low frequencies, is the low shelf, and band 5, high frequencies, is the high shelf.
But these two bands each have two different settings. The small left icon, next to the LF and HF, is called a bell-type EQ. It kind of looks like -o-. This will either boost or cut a section of frequencies set by you with the frequency knob. The ‘Q’ knob will determine how wide or narrow the bell curve will be. A low Q setting will give you a wide band of frequencies, and a high Q will render a narrow band of frequencies. A good rule of thumb is wide when boosting and narrow when cutting.
The typical use for this is to, say, boost the lower frequencies to bring out a kick drum or synth bass. On the high end, with the HF knob, we can boost upper ‘air’ frequencies to make guitars or vocals stand out or sound brighter. Of course, we can also cut in these frequency ranges as well.
The other icon setting is called a ‘shelf.’ This is the more common use for these two bands. Typically we use a boost here (low or high). When boosted, it looks just like a “shelf.” If on the low shelf, we set the frequency knob to 125 Hz, then everything from 125 on down (to 20 Hz) is boosted the same amount. On the high shelf, we might add a shelf for vocals starting at 6 kHz. In this case everything from 6 k up will have a boost. Of course, we can also cut using a shelf, but this happens less often then a boost.
The Q factor is a bit more complicated and will have to be reserved for another post.
Bands 2, 3 and 4 allow for bell curve settings only. These are the same as the bell curves on bands 1 and 5. These are used for low-mid, mid, and high-mid frequencies. There are only three knobs: Frequency, Gain and Q. Frequency, of course, sets the frequency that you want to work with. Gain is volume (loudness) and can be plus (positive) or minus (negative). We might say boost 2 kHz 2 dB (2 dB) which is a positive gain. Or cut 1200 Hz 3 dB (-3 dB) which would be a negative gain.
As stated above, Q determines the amount of frequencies being altered by the EQ.
Throughout my blog series on EQs I am going to refer to the free EQ plugin that comes with Pro Tools, the Digirack EQ III 7-band. First, let’s talk about the input/output LED meters and gain controls (top left of the plugin). This simply shows the input and output signal level running through the EQ. Always check to make sure there is no clipping going on. If on the input or output side the signal is clipping, hitting red, simply turn the respective gain knob down until there is no longer any clipping happening. It is normal to adjust these gain knobs. With the input gain knob is a symbol, Ø. This is the polarity switch “button.” This will invert the phase of the incoming signal. If you don’t know what this is, I will cover it in a later post. It’s a little more advanced, but easy to understand and know when to use. For now, it won’t concern us.
Just beneath the input/output section are two filters. There is a high pass filter and low pass filter (HPF, LPF).
High Pass FilterLow Pass Filter
There is also a notch filter. It looks like a line with a ‘V’ in the middle of it. (I couldn’t find a pic of one.)
-∨- (notch filter)
The high pass filter alllows high frequencies to pass through the EQ, while cutting low frequencies, not allowing them to go through the EQ. Conversely, the low pass filter allows low frequencies to pass through and cuts high frequencies. The notch filter takes a small section of audio and makes a deep cut (-12 dB or more). It takes a “notch” out of a small section of audio frequencies. The frequency can be set by the user. One use for the notch filter is for plosives on a vocal track. When a vocalist pops, say a ‘p,’ set the notch filter at 100 Hz. It should diminish it greatly or make it go away completely. You may have to sweep the EQ up or down a little to take care of it.
The two filters each have an “IN” button to engage them. They will light up blue when engaged. The frequency, of course, can be set to whatever you want.
Lastly, there is a setting that is used for the HPF/LPFs that tells the filter how steep of a cutoff you want. If we are allowing high frequencies to pass through and cut out low frequencies, how strong do we want to cut off those low frequencies? The slope is set per octave. The setting choices are 6 dB per octave, 12 dB/oct, 18 dB/oct, and 24 dB/oct. As an example, let’s say I set a high pass filter at 200 Hz, with a 12 dB/octave slope. What this means is that only frequencies above 200 Hz will pass through the EQ (and anything further in the signal chain), and frequencies one octave down (100 Hz, remember from my previous post?), will be 12 dB quieter. Another octave down, 50 Hz it will be another 12 dB quieter. There are times we want a steep cutoff, like 24 dB/octave and other times when we might want 6 dB/octave.
Look on the left side of the GUI window, which shows the graphic interface. There are small numbers. On the center line is 0. This is where all EQ bands start. In out example, since we’re cutting at 200 Hz, at 100 Hz the downward slope will be at -12 dB. At 50 Hz it will be -24 dB.
I hope this hasn’t been too confusing. Try experimenting with these filters on a mix you’re working on. Keep your ears open when doing this. You can even experiment on a piano or acoustic guitar track. Set the HPF up higher, like 400, 500 Hz. Change the different octave settings. You should hear what’s happening.
![EQ – Different Frequency Bands [20 Hz – 20 kHz]](https://doublesharprecording.files.wordpress.com/2022/07/sound-frequency-spectrum-and-subjective-ranges.jpg?w=1172)
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