An inside Look at Different Tone Controls and What They Do

There many gadgets on amplifiers and effects units which can help you taper the sound to your liking. Here's a brief description of tone control circuits you can find on your rig and how they affect your sound:

The Simple Tone Control:

This is the simplest and most limited form of equalizer. You can even find one on your guitar and on most effects pedals. It just makes the sound brighter or duller. It consists of a capacitor and a potentiometer (or 'pot'). The more you turn it to the left, the more the sound goes through the capacitor before leaving the guitar.


The Tone Stack:

Most guitar amplifiers nowadays come with at least the traditional highs, mids and lows tone stack. This is simple enough and you don't have to bust your head to realize what happens when you boost or cut each frequency. Good guitar amplifiers don't usually need to be equalized and a zero gain setting for these knobs (in the middle) should be good for most purposes because the manufacturer took the time to design it properly for musical instrument applications and maybe just a slight boost or cut is necessary to get YOUR personal sound.

Highs: This depends on the manufacturer and model, but your highs on a guitar amp are probably a shelving (or slope) filter anchored at about 3KHz if you need to brighten your sound or make it a little duller.

Mids: The mids are a bow shape filter whose anchor point is about 800Hz and can affect everything between about 100 Hz to 2 KHz. Obviously the control affects the 800 Hz frequency most and the more you boost or cut the the mids, the more the surrounding frequencies will be affected. These are very important for your sound because they control how much presence you want. If you turn the mids down too low, you're sacrificing important frequencies needed to be able to hear yourself. If you turn them up too high, you get a very irritating sound (1 KHz at high volume is unbearable for most people)

Lows: Another shelving or slope filter that cuts or boosts anything under 300 Hz although it's weak at this point, it exponentially affects the lower frequencies to a greater extent. It's usually anchored at about 100 Hz. This knob controls how much body you want in your sound. When your playing in a hall with lots of reverb, you may want to bring it down just slightly and if your playing outdoors you may need to turn it up a bit so your sound projects further.

For guitar sound, you usually have to just equalize it in the practic hall and keep it the same for most purposes whereas Bass players have a more difficult time with sound because they work with frequencies that behave very differently in different places depending on the acoustics.


The Graphic Equalizer

These became popular in home entertainment systems in the late 70's and for guitar and bass players in the early 80's. It's a complex filter composed of sliders. You don't usually see them on a guitar amp, but a lot of guitarists have a 5 or 7 band graphic equalizer as one of their pedals.



As it's name suggests, the sliders are laid out as if you were looking at a graph and each slider affects the labeled frequency. Each one of these sliders is a high 'Q' filter (very sharp curve), but as you go to the extremes (plus or minus 12 or 15dB), it will affect the other surrounding frequencies also.



One of the first things I did when I bought mine about 20 years ago was to give it the good ol' 'V' shape, cause I wanted to make my guitar sound 'heavy'. Well, I don't know if I'm getting old or what, but for the last 15 years I only been using it flat with just a tad more volume for when I'm playing solos. For me, these gadgets are more useful for bass players and sound reinforcement systems like PA's and monitoring (PA system = public address system).

The Parametric EQ:

What the heck is a parametric EQ anyway?

A fully parametric equalizer is a filter composed of three knobs. One controls the gain of the selected frequency, another controls the frequency to be boosted or cut and the other knob adjusts the quality of the filter.

Gain: Controls the boost or cut of a certain frequency (usually plus or minus 12 or 15dB).

Frequency: Depending on whether it's for hi-mids or lo mids, it can select from about 100Hz to 8 KHz. Again, this will vary depending on whether there are one or two parametric equalizers for a mixer channel or just one. If there are two parametrics for mids on a channel, one may sweep from 100Hz to about 1 KHz (low mids) and the other from 1 to 8 KHz (high mids). You'll only have to deal with these in large recording studio and big concert consoles.

Quality or 'Q': This knob controls how fine the filter will be. A high Q filter affects the frequencies around it very little where a low Q filter affects the frequency selected, but also the surrounding frequencies a lot more. To understand this more easily, just imagine a high Q filter as a thin arrow and a low Q filter as a gentle bow across the frequency spectrum. Equalizers without this knob are considered semi perimetric EQ's, which are more practical for most situations.

A word of caution!
When using equalizers, you should always start from zero (no gain or cut on any frequency) when you start experimenting. It's important to remember that after a certain time your ears become saturated and what sounded good at home all by yourself may be useless in the practice hall or for a live performance. It's important to have some sort of reference for the sound you're looking to get (a good recording of that sound or an effects pedal you know sounds good).

My experience with the Boss Metal Zone about 10 years ago can help you understand this concept a little better:

I started working with it without a reference and thought I had a really good sound happening. Then, when I used it during a gig, it sounded like some insect buzzing around the stage. It was horrible! I immediately by-passed it and kept using my Korg OVD-1 for the rest of the show.

The Korg OVD-1 pedal (built like a tank! and discontinued) that I purchased in 1985 is MY favourite pedal. It's even better than the TS-9 (Tube Screamer) in my opinion, because it's got a tighter bottom end. If you can get your hands on one of these gems, you won't regret it. It's a good all-purpose overdrive!

As the story goes, I placed both the Korg OVD-1 and the Boss Metal Zone side by side, so as to compare their sound and use the Korg as a reference. It's not that I wanted them to sound the same (that's absurd!), but I was looking to give the Metal Zone similar tonal qualities. This is very important, because when you switch from one pedal to the other, you don't get an abysmal difference in sound.

First, I set the Metal Zone's EQ to zero and the distortion half way. I then switched back & forth (one 'on' while the other is by-passed). I first noticed that the highs were too loud and turned them down to 9 o'clock. This helped quite a bit.

After that I played with the lows. This knob also had to be turned down, but just enough to remove the boomey sound (If you overdo it you'll get that transistor radio effect). All this was done switching back and forth between the pedals (The Korg being my tonal reference).

Next it was time to play with the semi-parametric for the mids. The sound was not too bad already after fixing the highs & lows so I gave it a slight dB cut (no more than 11 o'clock) and started sweeping the mids very slightly around the center frequency until I thought the tone was acceptable. I took a break at that point and didn't get back to listening to it until the next day.

The next day, I realized that there was really no need to cut the mids for the desired tone, so I left both these knobs at zero (half-way) and then tried it in the practice hall. There, I just had to do some slight changes (reducing distortion to about 10 o'clock, adjusting the mids, highs & lows a bit, etc), but I got it sounding like a good compliment to my sound for when I needed something heavier than an overdrive.

A Common Mistake
Don't make the mistake of thinking that a sound you thought was great at home will sound the same when playing with other instruments. It's common for Heavy Metal guitarists to cut the mids producing a bassey/trebly sound and then wondering why they can't hear what they're playing at the practice when everybody's complaining about their volume.

The problem is that they cut out the frequencies necessary to distinguish notes and chords. The presence of an electric guitar is around 2KHz, if this is cut severely, you can't distinguish what you're playing, and when your guitar has to compete with other instruments, you'll be turning up your amp to hear yourself and you'll get complaints!


Final Words
Equalizers can be very useful when looking for that sound that you can't find any other way. But remember, 'Don't fix it if it ain't broke'. A lot of sound problems can be fixed just by setting all EQ knobs at zero gain. Equalizing usually works best cutting frequencies that are too loud instead of boosting what was never there to begin with.