Lead Tone 4: EQ and Distortion Voicing

There are many ways of using EQ to enhance tone. Pickups all have their own EQ curves, and amplifiers have distinct mid-scoops which affect the final tone, and also there is the response curve of the speaker which rolls off the upper frequencies. This post finishes our look at distortion and introduces EQ by focusing on using EQ to ‘voice’ the distortion.


Pre- and Post- Distortion EQ

Putting the EQ before the distortion is completely different to EQ after distortion. For instance a pre-dist EQ boost at 3kHz would result in the distortion stage clipping the 1kHz region more than the rest of the signal. Post-dist EQ can not have any effect on how the distortion is clipped, because it follows the distortion. Put simply, pre-dist EQ will change the clipping character of the distortion, but post-dist eq will only shapes the already-distorted sound. The way that pre-dist eq interacts with the clipping stage is known as distortion voicing.

The most common everyday example of pre- versus post- distortion EQ are typical Marshall and Fender amps. The tone stack in a Marshall amp typicall follows the clipping stage whereas the tone stack in a Fender amp is usually before the clipping stage (obviously there are many other differences between the typical Marshall and Fender designs which create their sounds – but its outside the scope of this series).

Distortion voicing

Voicing is probably the most important part of distortion and overdrive, and has more influence on the ‘character’ of the distortion than virtually anything else. Remember that several parts of the signal chain distort, so the concept of distortion voicing can apply to all of those areas. For simplicity though, this post focuses on voicing the pre-amp distortion – since this is where deliberate control of distortion voicing usually happens.

The best way to learn about voicing is to experiment. I learned by buying an EQ and an amp modeler – and then spending hours trying to understand how the EQ would interact with different amp models, and how the effect of having the EQ before the distortion was very, very different to placing the pedal in the effects loop.

Pre-Distortion EQ

What I learned was that a small increase in treble before the distortion would create a clearer, ‘fluid’ character, and adding even more treble would create a ‘gritty’ sound. Adding a little bass before the distortion sounded ‘smooth’, but would quickly develop a ‘crusty’ quality if I added too much.

Adding treble before the distortion can allow for more gain before the tone of the guitar begins to breakup too much, so a trebley distortion will usually sound clearer than a bassy distortion with the same gain setting. From what I understand this is because the loudest overtones being generated by the distortion are higher than the fundamental and the lower harmonics of the string. This means that more of the original guitar sound is able to get through – I’m not an acoustic- or electrical- engineer though so I can’t be certain, but this is definitely how it sounds when you listen and compare the two.

Conversely, adding bass before the distortion creates a thicker and more densely distorted tone because the natural harmonics from the string, and the harmonics generated from the distortion would be sharing similar frequency ranges. Depending on how many clipping stages are in the unit, this could also increase intermodulation distortion.

A Case Against EQ Pedals

Although I learned distortion voicing using an EQ pedal, I don’t normally use these anymore since the frequency bands are far too narrow – this is great if you are wanting a ‘cocked wah’ effect, but not very useful for more subtle voicing.

Some people recommend parametric EQs as the ultimate control of distortion voicing. Parametric EQs would be a great tool, but unfortunately decent parametric EQs are rackmount and (usually) very expensive. I went through a phase where I was obsessed with owning two rackmount parametric EQs (one each for pre and post distortion) and I very nearly dropped a lot of money on them too…

… but fortunately I found a new approach before I emptied my bank account, and found options which are simpler to operate, cheaper but still very versatile. Rather than the narrow bands of graphic EQs or the ‘surgical correction’ possibilities or parametric EQs, I recommend only one or two boosts or cuts over a wide frequency bandwidth. Usually, this comes down to a few ‘booster’ pedals with specific EQ character, and sensible pickup selection.

Guitar Mods for Pre-Dist EQ

For good, subtle but effective, control of your distortion voicing I recommend you listen carefully when you first buy new guitars. The EQ of the guitar itself is obviously the primary source of ‘pre-distortion EQ’. Once you have a good guitar with a tone in-the-ballpark or what you are after you can consider a few simple guitar mods. Adding phase, parallel, series, coil tapping, coil splitting, and blender-knob options to a guitar is a great (almost costless) way of finding new tones from an instrument without buying new pickups, and if you are worried about changing the look of your guitar you can often use push-pull pots instead of drilling new holes.

Most people find that stock guitar tone controls tend to only muddy the sound without really offering any actual control of the tone, but simply changing the capacitor to a lower value will often make the tone control far more usable. Also, most tone controls are simply low pass filters (high-cuts), but there are other options. ‘Stepped’ tone controls, Fenders TBX, THD ToneCurve, Varitone, and the various active options from EMG are all viable options, and are great for influencing the quality of the distortion.

Pickup Change

Changing pickups is obviously more expensive than the other options but can yield good results, provided you make a very careful choice. If you have a look at the high output Dimarzios, EMGs or other ‘metal’ pickups, you’ll see that they usually have a fairly bright response – perfect to retain definition and clarity with high-gain amplifiers. Similarly blues players often choose vintage humbuckers or single-coils, with a typically more ‘middy’ response. The humbuckers give a crusty blues/rock owing to the mid-boost being focused further down the frequency spectrum. The single coils, having a upper-mid emphasis give a grittier SRV or Hendrix sound, with clearer, more articulate bass end.

Boost Pedals with Tonal Characteristics

For very high gain tones, you might like to try a treble boost pedal. The treble boost allows you to have more gain with greater definition, and serves a similar function to using wider-bandwidth pickups.

For lower gain or blues players, you’ll probably want a fairly wide mid-boost. For this you could look for special treble-boosters or clean-boosters which have a switch to change them to a mid-boost. Alternatively, you might like to try the classic trick of running a Tubescreamer set to to a low drive, but high level setting. Tubescreamers naturally have a low-cut and mid-boot which can often help to get a crunchier, ballsier overdrive from the amp. This trick was commonly used by SRV.

Post-Distortion EQ

This is generally any EQ which goes into the effects loop after the pre-amp but before the power-amp. This is used to shape the final tone, and unlike pre-dist EQ has no effect on the distortion character, unless you are voicing the power-amp distortion…

Voicing the Power-Amp Distortion

Obviously, if you are using significant power-amp distortion then the EQ in the effects loop will have less effect on the final tone. In this instance any effects-loop EQ will serve the purpose of voicing the power-amp distortion. Same principles apply as voicing the pre-amp – treble for higher gain with more clarity, bassier for lower-gain but with noticeable breakup.

One thing to consider is that if your power stage is overdriving then you have very few options in controlling the final post-distortion EQ curve. Obviously the cabinet (whether open- or closed- back) will affect the tone, as will the speaker selection to roll-off the top end. But you don’t have a full treble, mid, bass, tone stack to fiddle with so you need to be careful when selecting cabinets and speakers because you can’t adjust them (although there are a few tricks, such as stuffing the cabinet with absorbent foam, or drilling ‘ports’ in the back or closed cabinets. or stuffing the ports up with foam – this will generally tighten the bass up a bit).

Also, bear in mind that for recorded guitar tones or live tones being fed through a PA, the final post EQ is more a result of the microphone choice, the mixing board, and any EQ settings that the front-of-house or the mixing engineer use to alter the sound.

To be continued…

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One Comment

  1. Ijon says:

    Very useful articles and very helpful.

    Could you please explain more the statement of yours below. I mean what kind of boosters do you use for what kind of settings (mild overdrive, moderate gain, hi gain). And finally what is relevance of amp pre-amp/power-amp gain or volume levels there ?

    … but fortunately I found a new approach before I emptied my bank account, and found options which are simpler to operate, cheaper but still very versatile. Rather than the narrow bands of graphic EQs or the ’surgical correction’ possibilities or parametric EQs, I recommend only one or two boosts or cuts over a wide frequency bandwidth. Usually, this comes down to a few ‘booster’ pedals with specific EQ character, and sensible pickup selection.

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