“You know, I’ve been doing sound here at my church for about two years now, and there are a couple of things that aren’t quite clear to me. First, where’s the bass and treble control? And, what are these knobs for - the ones on the console labeled high, mid and low?”
I’ve heard questions like this posed more than once by people who do sound at their churches. And they’re great questions. Remember - we’re all in this together!
The short answer is that the knobs are for an audio process called equalization, typically shortened to EQ. Together, the knobs make up the console’s EQ section, which allows the operator to more finely tailor the sound.
Let’s start by taking a look at the EQ section. (Refer to the graphic example below right.)
This image shows a typical example of a rather basic EQ section found on each channel of consoles that are very commonly used with church sound systems.
Note that every knob and button included on a console channel - EQ section and every other one -apply only to that specific channel, not the entire console.As you can see, there are three separate EQ knobs on the channel, one each for high frequencies, mid-range frequencies, and low frequencies. If we turn any of these knobs to the left, we are “turning down” those frequencies, and if we turn any of them to the right, we are “turning up” those frequencies.
Note that in audio terminology, this is also sometimes referred to as “boost” and “cut” – as in “boosting” (turning up) some frequencies and “cutting” (turning down) some frequencies.
A Simple Way
It’s important to understand the frequencies controlled by these three primary knobs. A simple way is to equate it with a home stereo: the high frequency knob equates to those frequencies controlled by the home stereo’s treble knob, and the low-frequency knob equates to the home stereo’s bass knob.
Most console EQ high frequency knobs are centered at about 12,000 hertz, usually abbreviated to 12 kHz (kilohertz ), and this is a measure of cycles per second. (In this case, 12 kHz equals 12,000 cycles per second. The more cycles, the higher in pitch the frequency.)
For musicians, 12 kHz translates to the note F-sharp in the ninth octave on the piano. Or in simple layman’s terms, 12 kHz is pretty high.
What we’re trying to achieve with high frequencies are things like adding “crispness” to an instrument or taking the harsh “s” sounds out of a speaking or singing voice. On most consoles, this knob controls what is called a shelf filter. Starting at the 12 kHz frequency, turning this
control will effect all frequencies above 12 kHz.
In other words, by turning this knob to the right, frequencies above 12 kHz are boosted, normally with a maximum boost of 12 dB per octave. One octave means affecting all frequencies up to 24 kHz. Turning it up too much can cause serious damage to the high-frequency section of loudspeakers, so caution is advised.
And, it follows that turning this knob to the left will cut these same frequencies. Just remember: using this control effects a broad frequency range so be aware of when cutting or boosting - do so only in small steps.
Moving To The Lows
Much the same is true of the low-frequency knob. It’s usually centered at about 80 Hz, and is used to enhance the bass level and signature of vocals and low-frequency instruments. This is also a shelf type filter, like the high frequency control knob, and it controls about a two-octave area.
It boosts low frequencies at 80 Hz to 160 Hz, and cuts low frequencies at 80 Hz to 40 Hz. Again, every time the frequency is doubled or halved, it represents one octave of frequency range.
Excessive low frequency adjustment is far less likely to cause damage to loudspeakers. However; because low-frequency signals are made up of larger sound waves that tend to go “everywhere” and often cause feedback, we can use this knob to cut those frequencies back.
In general, with microphones on console channels being used for vocalists and pastors, you will want to turn down the low frequency on those channels to reduce the tendency for low-end rumble, and also to help speech intelligibility. (Eliminating the rumble will bring more clarity to the vocal signal.)
Another feature offered on some consoles is a low-cut filter on each channel. Pressing this button does just what the name implies – it cuts the low-frequency EQ.
Now, what about the mid-range knob? Nothing that corresponds to the mid-range can be found on most home stereos - rather, mid-range on the home stereo is a combination of the bass and treble knobs.
However, on the console, the mid-range control doesn’t work exactly the same as the high- and low-frequency controls. When it is boosted or cut, it adjusts the frequencies on both sides of the center frequency.
So if the center frequency of the mid-range control is 3 kHz, it will effect frequencies as high as 6 kHz and as low as 1.5 kHz. By the way, this two-octave range of frequencies comprises most of what we hear, and is also at the heart of most human voices.
The overall mid-range frequency band can be as low as 100 Hz and up to as high as 3 kHz. A bass instrument typically plays from about 30 Hz up to about 240 Hz, while a bass vocalist (think gospel quartet) is in the 55 Hz to 500 Hz.
All vocalists, from the lowest frequencies to the highest, will therefore range from about 55 Hz and up, all the way to about 1.7 kHz (think soprano). This is then the frequency range where we can make the voice of the person speaking or singing sound crisp and clear (or dull and lifeless).
Note that some consoles are now also equipped with a “mid-low” frequency and/or “mid-high” frequency knobs. Simply, these knobs provide the operator with even more ability to adjust and fine-tune the crucial frequencies in the mid-range. (Again, it’s the frequency range of what we hear most.)
Just A Little Time
So, how do you get comfortable using these controls? It’s not difficult and can be fun if you enjoy your calling and have a little time. Just plug a mic into the console start to speak into it, and set all three knobs straight up to “0” - no cut, no boost.
While talking, cut and then boost the high knob, and note the effect it has on your voice. Then do this with each control so you can hear what happens in each frequency range.
There is no magic here, and not much to fear unless you like to listen at real high levels. By the way, I highly recommend doing this too. Turn it up until some feedback is produced and see which frequency range cuts out the feedback. (This is best done when others aren’t present.)
Also play some music through the system and do the same cuts and boosts. You’ll soon be surprised at what you hear and don’t hear.
The point is to understand the frequencies and what they correlate to, and to be up-to-speed on using the EQ knobs to tailor the sound for pleasing and effective results.
The next time you’re working “live” with a person speaking or performance, you’ll then know how to make it sound even better.
Joe Wisler has worked in professional audio for more than 30 years and has also been involved with church sound and technical ministry throughout that period. Courtesy ProSoundWeb
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