What Compression Does

Dynamic range compression is essentially an automatic volume control, where loud sounds (above a given threshold) are automatically reduced in level. This means that the dynamic range of the output signal is less than the input signal – hence the name compressor.

Its important to understand that compressors only pull down loud sounds – they are not designed to raise quiet sounds. As such the overall output of a compressor circuit will be lower in level than the input. To counter this loss of level, compressors are typically fitted with an output gain knob – commonly labeled ‘makeup’ gain since – to bring the overall signal back up to a desired level. Thus, the net effect of the compressor is that the low-level sounds are increased in volume. Bear in mind that noise is a low-level sound, so compressors will also raise the noise floor.

How Compression Is Used

Typical guitar pedal compressors are very limited in features compared to rack-mount studio compressors, so only some of the following knobs are likely to be found on any one guitar pedal:

• Threshold
• Ratio
• Attack
• Release
• Output Level/Make-Up Gain

Of course, true ‘studio’ rack compressors have far more functions than those listed here, but these are the basic controls which you are most likely to encounter.

Threshold

Only when the input level exceeds the threshold will the compressor begin to attenuate the level – signals below this threshold are normally not effected by the compressor circuit. So a lower threshold means the signal is being effected more often, whereas a very high threshold will only be affecting the very loudest parts of the signal.

Unfortunately, on all but the best guitar pedal compressors, the threshold is usually set at the factory, and there is no way for the end user to adjust it. The only pedals I’m aware of with a threshold control are the Carl Martin Compressor/Limiter, and the BYOC 5 Knob Compressor. The Joe Meek FloorQ uses a ‘Input Gain’ knob which serves essentially the same function as a threshold control.

Ratio

The ratio controls the output level relative to the input level. For example, 3:1 would mean that an input signal 3dB above the threshold, would result in an output level only 1dB above the threshold. Again, for all but the best guitar compressors, the ratio is usually set at the factory. Both the Carl Martin and the BYOC have a ratio knob as does the Joe Meek though this pedal has the ratio control marked as ‘slope’.

Also EHX’s Black Finger and White Finger both have a switch marked as squash/norm which is similar to switching between a high ratio (squash) and a lower ratio (norm). Of course, since this is a binary switch not a knob, its either one or the other – you can’t have all variations in between.

Attack and Release

The attack setting is the time that it takes for the compressor to begin acting on the signal once it has passed the threshold. For instance setting a very short attack time will cause the attack of the note (the ‘picked’ part of the note) to be compressed. This is common for chicken pickin’ and funk guitar sounds. Conversely, for a more natural compression which preserves the natural attack of the guitar, a sufficiently long attack time will ensure that the attack passes through un-compressed and that the compressor only acts on the sustain of the note envelope.

The release is exactly the opposite to the attack control, meaning that it is the time taken for the compressor to reach zero gain reduction, once the input signal drops below the threshold. The release time should generally be set as short as possible provided that ‘pumping’ is not audible. ‘Pumping’ is where you can hear the compressor turning the level back up to zero gain reduction.

Most guitar compressors have the attack and release controls combined into a single knob, which is the case for the Carl Martin, BOSS, Behringer, DOD and Digitech products. Both the EHX Black Finger and White Finger have a switch for Lamp/LED which essentially switches between two different preset attack times. Vox’s Snake Charmer, the BYOC and the FloorQ are the only guitar pedals that I’m aware of with independent attack and release controls.

The ‘Sustain’ Knob

Many stomp box compressors have a ‘sustain’ knob. In reality there is no standard function for a sustain knob because the sustain due to compression is actually a combination of the ratio, threshold, attack and release settings. As far as I’m aware, most of the pedals with a sustain knob (such as the BOSS, Behringer and Digitech) are designed so that full counter-clockwise is a limiting function, while full clockwise provides maximum sustain.

For the limiting function the ‘sustain’ knob would shorten the attack as much as possible, and raise both the ratio and threshold. But at full counter-clockwise both the ratio and threshold would be quite low and the attack time would be lengthened. Since these pedals also have a dedicated attack control, I can only assume that the attack control sets a range of possible attack times, from which the final attack time is determined from the setting of the ‘sustain’ control.

Chances are that the release times are automatic – i.e. program dependent – which is a sensible choice for a guitar stomp box compressor.

Where Should the Compression Go?

The typical answer is compression belongs at the start of the effects chain (or maybe after filter effects), but such a simplistic view can limit your tonal options. Compression is used to control and modify dynamics. And wherever dynamics need to be controlled – compression may be suitable.

In recording studios it can go right at the front of a recording chain – to ensure hot levels, without distortion – or it can be the final processing on a complete mix prior to CD replication. Compression has a use at every point along the signal chain.

Think back to Lead Guitar Tone Part 2 where I talked about the balancing act of complexity and interest, versus focus and clarity. Compression increases apparent loudness (focus) at the expense of expressive dynamics (interest). So what you may gain in thickness of tone, you could lose in expression and ‘feel’. Its always a balancing act, so use your ears to make the final judgment.

So, where should compression go? Anywhere dynamic range needs evening out.

Evening-out Distortion – Compressing at the Front of the Chain

Many pre-amps and OD/Dist pedals are designed to be dynamically responsive, where picking hard increases overdrive, but playing gently cleans up the tone. But depending on the song or player, this can be an unwanted feature.

Putting a compressor at the front of the effects chain controls the dynamics before the signal gets to the pre-amp/overdrive/distortion. This gives the player a solid and predictable amount of crunch. This is an easy way of cleaning up poor picking technique, and is a way of driving the pre-amp harder for longer, but without overly clipping the attacks of the note. In this case the compressor is used to produce a even predictable overdrive. This creates a more focused driven tone which is particularly useful in denser arrangements, or when the guitar part is not the center of attention, such as crunchy chordal backing (but really I can’t think of anytime that the guitar shouldn’t be the center of attention, right up front in the mix ).

Evening-out Overall Dynamics – Compressing at the End of the Chain

In some contexts, particularly live band playing, dynamic players may have an unpredictable base level. This makes life hard for fellow band mates and for the front-of-house sound engineer. In these cases, compression is an effective way of decreasing your dynamic range from, say, 40dB to 15dB or even less. This way picking softly still seems like your playing softer, but in actuality your level doesn’t drop out of the mix. Conversely, picking hard will create the impression of playing harder/aggressively, without swamping out your band-mates.

Certainly, putting the compressor up front will even out the levels too, but for players who prefer a dynamically responsive, expressive distortion, it makes no sense to put a compressor before the overdrive. From a practical point of view, compression at the end of the chain can help you sit better in the mix, and ensures that no matter what amount of drive (high gain, crunch, or clean) you can always have a predictable output level.

Bear in mind though, if you go this route, you may want to have a boost pedal after your compression so that you can kick in a little extra level for solos – otherwise, without the boost, your lead tones and rhythm tones would have about the same level.

Make up your own mind about where to put compression. You shouldn’t necessarily put compression at the front of the chain just because everyone else does.

Squashed Attack

Although the attack control essentially exists to allow the attack to pass through unaffected, it is common for guitarists to use it for exactly the opposite. By setting the attack time to zero (or as close as possible), and the ratio and threshold fairly low, you can almost completely remove the attack from the note. This creates a percussive ‘thud’ rather than a ‘twang’ (highly technical terms ) at the beginning of the note. This effect is common in funk music or country.

Unfortunately ‘thud’ and ‘twang’ probably aren’t helpful descriptive terms for someone who has never heard a squashed attack, so heres an audio clip which should make more sense:

mp3 coming soon.

Parallel Compression

The attack of single notes are different to the attacks of strummed chords. Similarly a guitar pick has a different attack to finger-picking. And lets not forget that different guitars, pickups and string gauges all have differing attack characteristics. But if you like to keep your attack fairly ‘transparent’ and uncompressed, it will be virtually impossible to find a single good attack setting to suit all of these different scenarios.

As I said at the beginning of this article most all compressors work by reducing the level of the louder sounds, which may include the attack of the note if the ‘attack’ knob is not set properly. Then, by boosting the entire signal we end up with the net affect of boosting low-level sounds. But if we want to have a nice, transparent attack, where one setting works equally well over a variety of input signals we need a compressor which works the other way around – a compressor that boosts quiet sounds without first reducing louder sounds such as the attack.

So, in this instance, an ideal compressor would be one which left the attack of the note alone completely and only worked on the sustain and tail portion of the note… enter parallel compression.

Parallel compression is where the original (uncompressed) signal is mixed back in with the compressed signal. This restores our attacks and transients to their original state, and by increasing or decreasing the mix level of the compressed signal we effectively have a single knob controlling how much ‘tail’ or low-level signal we want dialed in.

This means that if you need to have just one compressor set up for a variety of situations or guitars, and want only to thicken the tails while allowing the attacks to pass through virtually untouched, parallel compression may just be the ticket.

Unfortunately there are very few guitar compressors with a dedicated blend control for mixing in the uncompressed signal. The only two that I’m aware of are the BYOC 5 Knob Compressor and the Barber Tone Press. Alternatively you might like to use a regular guitar compressor and then add a blender so that you can mix in the uncompressed signal. Good blenders include the Xotic X-Blender and the Morely FX Blender

And that pretty much concludes everything about basic lead guitar tone, since we have already covered EQ, overdrive, and distortion voicing in previous posts. In the later installments I’ll look at time based effects such as delay and reverb, and also some of the more ‘genre specific’ effects such as filter effects, including wah and phaser.

Equal-Loudness Contours

The equal loudness curves represent the way our ears are most sensitive to the high-end and bottom-end at high volumes; while at low volumes, our ears are most sensitive to the midrange (circa 4kHz). Effectively, this means that at high volumes our perception colours the sound with a wide mid-scoop.

You may be familiar with the ‘loudness’ button on old cassette players and even some CD players or music software? These are special tone controls which replicate this mid scoop but at lower levels, creating an impression of loudness without actually raising the SPL.

Similarly, a guitar tone with scooped mids will seem louder than a more middy guitar tone at the same level.

Mid-Scooping

Since scooped tones seem louder, tighter and ‘punchier’, many guitarists like to scoop the tone especially when practising at (low) bedroom levels. If you do this, remember that the guitar is an inherently mid-dominant instrument, so by scooping the mids we cut the most essential frequencies to a guitars sound.

Although mid-scooped tones sound acceptable at bedroom levels, they don’t translate well to stage levels or rehearsal levels. In these (louder) scenarios, the equal-loudness contour comes into play by scooping the mids out even more! Guitars rely on their mid frequencies to project and cut through mixes, but with such an extreme mid scoop these guitar tones quickly lose their tight bedroom sound, and instead become lost in the mix of the drums and bass.

Consider that by scooping the mids, you are now relying on the bass and treble of your tone to cut through – which is impossible since you’re competing with a bass guitar, and cymbals.

In band situations, play to the guitars’ tonal strengths. Keeping a healthy level of mids will help you cut through and be heard without needing to raise your level and risk ruining the balance of the band.

Amp Design

Also, a feature of guitar amplifiers is that they are also inherently mid-scooped. The mid scoop is so extreme that the only way to approximate a flat response is to turn the mid knob all the way up, and back off the high and bass knobs almost to zero. This means that even with the tone knobs set to 12 o’clock the tone is already being scooped considerably. Bear this in mind when ever you are adjusting your tone, and try avoid over-scooping the tone.

The Tone Stack

The tone stacks on most amps are generally broken into low, mid, high, and occasionally for even higher frequencies, ‘presence’. The more distortion that you have after the tone stack (such as strong power amp distortion) the less affect the tone stack will have. This is because distortion is a form of non-linear compression – the most prominent frequencies coming from the EQ section will be hit the hardest, so any peaks and dips in the EQ curve before the distortion will be ‘flattened’ out to some extent. So for tones with plenty of power-amp distortion the tone stack also serves as a pre-dist EQ of sorts. For lower power-amp gain, the effects of the tone stack will have more influence over the final tone. With higher power-amp gain the tone stack settings may need to be slightly exaggerated to achieve a similar effect.

Remember though that Fender style amps have the tone stack before the pre-amp distortion, so in this case, high pre-amp gain will also reduce the effectiveness of the tone controls. However since Fender amps are typically played at lower gain levels this rarely presents a problem. Also, you’ll notice that Fender tone stacks are capable of much more extreme EQing than most other amps – for instance few players will rarely set a bass knob on a Fender above three or four because this quickly becomes ‘too much’. As such Fender tone stacks have plenty of range even at full gain.

Top End Roll-Off

It is essential for the top end of an electric guitars tone to be rolled off, particularly if the tone is overdriven. The electric guitar itself has very little important high frequency information, (important content goes only high as 8-10kHz) but overdrive and distortion by their very nature, create overtones far above this range. These harmonics sit above the typical frequency spectrum of the main guitar sound. They sound separate from the main guitar tone, and they make the tone overly trebley.

So the solution is to have a low-pass filter (high-cut). Having a low-pass filter is not the same as simply turning down the high knob on the tone stack. A tone knob has a ‘bell’ or ‘peaking’ EQ whereas a low-pass filter is a shelving EQ.

The traditional way of getting the required low-pass filter is to simply use a speaker with a poor treble response. Larger speakers have a reduced treble response so electric guitar speakers are generally 10″-12″ in diameter.

In the modern ‘direct’ recording approach of home studios it has become common to bypass the power-amp and speaker entirely by running the output of the pre-amp straight into the desk or recorder. In this instance a low-pass filter can be applied during editing or mixing, or alternatively some guitarists use so-called ‘speaker simulators’ before the desk which contains low-pass filter circuit. In dense mixes, or mixes where the guitar is not a focal point, these approaches can be quite effective however they can not accurately replicate a real guitar speaker. Guitar speakers are a far from ideal low-pass filter, and they tend to add a peaky response to the mids. Also, when a guitar speaker is being driven hard (and, hey, it should always be loud shouldn’t it! ) a guitar speaker will also introduce fairly audible distortion of its own. Multi-speaker cabinets are even more difficult to emulate – since all sorts of phase cancellation and lobing will occur whenever multiple speakers are used.

Cabinet Design and Bass Response

While the design of the speaker probably has the most effect on the top end roll-off, the cabinet is probably the most significant factor influencing the bass end of a guitars tone. Bass is non-directional by nature and fills a room, whereas treble tends to ‘beam’ in a straight path.

Open backed cabinets disperse sound equally from the front and back of the speaker, however the sound coming from the front of the speaker is 180 degrees out-of-phase with the sound from the back. Since, bass is non-directional the bass from the front and back will combine and cancel each other. The very lowest frequencies are the least-directional, and become more directional as frequency increases, so the most cancellation occurs at the lowest frequencies with higher frequencies being canceled
progressively less. So open-backed cabinets tend to have a controlled but de-emphasised low end. Open-backed cabinets are typical of Fender combo amps, where the open-back serves to complement the bright sound which Fender amps are known for.

Another feature of open-backed cabinets is that they create a more open room-filling reverb sound. Because there is equal sound energy emanating from the back (away from the listener) as from the front, at least half of the final sound that a listener hears has followed an indirect path by bouncing of walls and objects before finally reaching the listener. Since closed-back cabinets only output sound from the front, the ratio of direct to reflected sound is much higher, so there is less room reverb in the tone.

Closed back cabinets tend to have a more prominent bass-end since the bass from the back of the speaker cannot combine with the bass from the front. They also have a more focused and directed sound, since they do not induce nearly as much room reverb as there is no sound emanating from the back. Since the sound from these cabinets is more ‘directed’ there is significant tonal variation depending on whether you stand right in front of the cabinet, or away and of to the side. Since treble frequencies beam more than lower frequencies, the further ‘of axis’ (to the side) you stand, the less treble will reach your ears, creating a darker sound.

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…

Distortion

The main aspects of distortion as it relates to tone are:

1. Type of Distortion – Hard or Soft Clipping
2. Symmetrical or asymmetrical distortion
3. Where the distortion occurs – at the pickups, the amp, the speaker or a combination of all three

Equally important, is the use of EQ to control the distortion ‘voicing’, but we’ll focus on that in the next post.

Types of Distortion

Its easiest to classify harmonic distortion as being ‘hard’ or ‘soft’ (or anywhere in between) and as being ‘symmetrical’ or ‘asymmetrical’. I’m not examining the solid-state versus tube debate, or the odd-order versus even-order harmonic distortion debate. From an engineering standpoint, solid-state devices can be designed to clip in ways very similar to old tube designs, while a poor design – whether tube or solid-state – will always sound pretty bad. There is no definitive difference between the sounds of a solid state or tube amp so listen, and decide for yourself.

‘Hard’ and ‘Soft’ Clipping

‘Clipping’ is what causes the effect of distortion, and gets its name from the peaks of the waveform being ‘clipped’ off.

This is a pure sine wave with no clipping

This is the same wave, but after clipping. The dotted line represents the original sine wave.

‘Hard’ and ‘soft’ refers to how ‘squarely’ the waveform is clipped. A very flat, square clipping characteristic is known as ‘hard’ clipping, and a rounder clipping shape is known as ‘soft’ clipping. Hard clipping is typically more complex, sounds more aggressive, and generates more harmonic content than soft clipping, which sounds more ‘overdriven’ and retains focus. Silicon fuzz pedals are a good example of hard clipping, whilst very early vintage tube/valve guitar amplifiers will give you an idea of softer clipping.

Hard Clipping

Soft Clipping

In the truer sense of the word, soft clipping refers more to the kinds of distortion found in analogue tape devices and the like. Compared to these soft clipping devices even the gentlest overdrive is really a hard-clipping device. But within the realms of guitar devices the softer clipping devices are usually clean amps, clean boosts, tube/FET based distortion units. The harder clipping units usually usually get their distortion from overdriven transitors.

Its important to understand that how hard or soft the clipping is, has little to do with where the ‘gain’ knob is set. The ‘gain’ controls how much clipping you have in the signal, but the actual clipping characteristic is determined in the design of the pedal or amp. Unfortunately most pedals/amps don’t offer a ‘clipping’ control where you can vary the ‘hardness’ and ‘softness’ of the clipping, so this is something you need to be aware of when purchasing you gear.

Occasionally you may come across ’boutique’ pedals or ‘mods’ for commercial pedals which will allow you to have some control over the clipping characteristic. These pedals usually achieve this by having a switch which will add/rearrange clipping diodes in the circuit. These are a great idea if done well, however be aware that these are only available with a switch – you can’t have a ‘knob’ which gradually changes from hard to soft clipping, its usually just one or the other.

Symmetric versus Asymmetric Clipping

So far all of the examples have been symmetric clipping, which is where both sides of the wave form are clipped the same. Asymmetric clipping, on the other hand, is where each side of the wave form can be clipped differently.

Symmetric clipping is more focused and clear, because it is only generating one set of harmonic overtones. Since asymmetric clipping can be hard-clipped on one side, and soft-clipped on the other, it has the potential to create very thick complex sounds. This means that if you want plenty of overtones, but do not want a lot of gain, asymmetric clipping can be useful. For full-blown distortion symmetric clipping is usually more suitable, since high-gain tones are already very harmonically complex.

Asymmetric clipping also seems to create more apparent intermodulation distortion (the bad kind of distortion). Also, since chords have more harmonic content than solo lines, it is a good idea to avoid chord playing whilst using asymmetric clipping. This helps to avoid objectionable levels of intermodulation distortion. Sticking with symmetrical clipping for rhythm parts helps ensure that your tone doesn’t become muddy and unclear.

Generally speaking, asymmetric clipping is believed to sound more like a real tube amp than symmetric clipping, since most common ‘hailed’ tube amp designs clip asymmetrically. However in my experience they both create very good useful sounds for different applications. Also its my understanding that the more expensive tube amps are actually designed to minimise the amount of asymmetry in the waveform.

Here is a clip with various riffs played at different gain levels. Each riff is first played through an Tubescreamer style pedal and then played again through a Super Distortion style pedal. These pedals are almost identical except that the Tubescreamer clips symmetrically and the Super Distortion clips asymmetrically.

MP3 DEMO OF ASYMMETRIC AND SYMMETRIC DISTORTION COMING SOON

Try these pedals out in your local music store if you want to investigate more. Neither of these pedals are fantastic sounding units (IMHO), but they do highlight the differences between asymmetric distortion and symmetric distortion quite well.

The circuits for the TS-808 and the SD-1 are very similar, so if you decide that you like both of these units for different purposes, you could consider buying one of them and then adding a switch to change the diode clipping arrangement. There are plenty or manufactures who produce kits for this kind of mod, and I wouldn’t be surprised if versions of these pedals exist that have a symmetric/asymmetric switch as standard.

One last note about symmetric versus asymmetric distortion, is that typically asymmetric clipping will have a predominant first harmonic, which the symmetric clipping will not. Many guitarists feel that this harmonic is essential to their tone.

My understanding is that a symmetric clipping circuit doesn’t have to have a diminished first harmonic, but just it is common that they do. Similarly not all asymmetric clipping circuits will have a dominant first harmonic, but it is common. This is because push-pull amplifier designs (which normally clip symmetrically), cancel out the even-order harmonics. Single-ended designs (which clip asymmetrically) do not result in the even-order harmonics being canceled out.

Its probably unclear whether those who favour asymmetrically clipping actually prefer the sound of the asymmetrical waveform, or just prefer the sound of the even-order harmonics. Most likely its a combination of each with more than a heavy hand of hoodoo/voodoo placebo effect thrown in there as well. Realistically they are both valid sounds and it just comes down to choice and personal preference.

Where Should the Distortion Occur

Pickups, OD/Distortion pedals, pre-amps, power-amps, and speakers all distort to some extent. The trick to a good tone is to know where the distortion should occur, and how you can combine distortion from different parts of the chain.

Distortion for High Gain Tones

Generally speaking higher gain tones should only have a few parts of the chain distorting since distorting distortion usually only serves to increase the noise floor, and does not create a very musical tone. This means that for very high gain tones you should probably rely mostly on pre-amp distortion or maybe even a separate pedal. Although there are people who will disagree with me on this point, I feel that high-gain tones need a minimum of pickup distortion and minimum power-amp distortion. Any extra distortion in those areas can only lead to increased levels of intermodulation distortion (I can hear the front three rows hissing and screaming “Blasphemer! Blasphemer! How dare he criticise the power-amp distortion?”) .

In some dedicated high gain amps the master section is relatively linear (i.e. introduces very little distortion), so turning up the master volume will still maintain a good clear, heavily distorted tone. But using a distortion pedal with a vintage style amp with the master volume turned up high, will often take definition and clarity away from the tone, and, in extreme cases, will result in a mushy fuzzy sound, with plenty of inter-modulation distortion (that’s distortion that we don’t want, remember?).

Since high-gain tones sound best with most of the distortion coming from the pre-amp, you should try to use a fairly ‘neutral’ pickup – or even a slightly bright pickup (see ‘voicing’ in the next post) – with a clear ‘hi-fi’ sound. Active pickups can work well, but there are plenty of passive pickups which suit perfectly as well – Dimarzio pickups are very common for this, though I have not used them personally.

As for the speaker choice, it is really personal preference. In my opinion a touch of speaker distortion actually works very well even for high gain sounds, but this is kind of counter-logical and you may disagree.

Overdrive for ‘Clean(er)’ Tones

For clean to overdriven sounds the distortion can be spread out through the chain a bit more. Often players will choose a more characterful, and complex sounding pickup (one with plenty of harmonics, thick sounding, or specific EQ etc), combined with a little pre-amp distortion and a significant amount of power-amp and speaker distortion.

For very subtle clean-overdrive, it is often the power section and the speaker distortion which creates richness of tone. However, Dumble amplifiers – a very revered amp among blues players for ‘mild crunch’ – are known for their use of ‘precision’ power-amps. These power amps were designed to create minimal distortion, so Dumble amps got most of their overdrive from the pre-amp.

‘Dirty’ Tones

For a straight-ahead rock tone – very dirty but not ‘high gain’ – I think that the power-stage is perhaps the most important part of achieving a decent tone. I feel that the power section is so important because it is effectively ‘distorting distortion’. In high gain sounds, distorting distortion is a bad idea since the tone is already very complex and adding more distortion simply makes the tone incomprehensible. But in a rock context in works quite well because it makes the sound very dirty and more complex, but because the tone isn’t soaked in huge amounts of pre-amp gain the overall tone still retains some focus. Hence, the tone sounds ‘very dirty’ but doesn’t sound like your using bucket loads of distortion either. (Afterthought: Maybe asymmetrical distortion might help create a ‘dirty but not high-gain’ sort of tone?)

Beware of intermodualtion distortion though when you try this idea. Van
Halen’s dimed ‘brown’ sound is probably as dirty as you can get before you will need to consider changing over to ‘modern’ high gain amps with more pre-amp distortion and less power-amp distortion. In fact, the intermodulation distortion that occurs in the brown sound is actually already very high, so Van Halen used ‘tempered’ tuning to allow him to play chords but still retain some clarity and focus – otherwise his tone may have just become mushy.

Sonny Landreth / Eric Johnson Lead Tone

Another great tone trick where distorting distortion works remarkably well, is running a fuzz pedal in front of an overdrive, or a dirty pre-amp. Usually we use fuzz pedals to create most of the distortion and then set the rest of the chain relatively ‘clean’, however Eric Johnson and Sonny Landreth, among others, use the fuzz pedal combined with an overdrive of some sort, to great effect.

This usually only works well with lead work, since any chordal playing will highlight the intermodulation distortion. Also it tends to work best with clearer sounding single coils as the more complex humbuckers tend to become too muddy with so much layered distortion. Unfortunately this means that you need to deal with single coil noise, combined with lots of distortion. It can be hard to get just right, but when you do it sounds complex, thick and lush, but with surprising clarity.

The Good and the Bad

Unfortunately what makes great tone so elusive is that usually any one change can have good or bad effects, depending on the situation. For instance, in the last post I mentioned how ‘scooping’ (cutting) the mids could create a smoother tone, but might also rob the tone of its ‘balls’; or how boosting the highs could create a brighter, more articulate sound, but might also cause your tone to become ear-bleedingly shrill and ‘ice-picky’.

Complexity vs. Focus / Interest vs. Simplicity

Unfortunately almost every decision you will make for your tone involves some kind of trade-off like this. To make tone decisions easier it’s helpful to think in terms of trading complexity for focus, and trading interest for simplicity.

The more complex your tone becomes, the harder it is for the listener to be able to comprehend what they are hearing. For instance, a twelve string guitar, with fuzz and distortion through two delay units and a hall reverb, would be incredibly complex in theory, but in reality it would simply sound unintelligible. Conversely, the simpler your tone is, the less interesting it becomes. Such as a cheap guitar, with characterless overtones, played in a dead room, and a boom-box instead of an amp.

It’s like language: very simple language is off-putting because it is too simplistic to communicate anything of value; on the other hand, overly flowery and difficult language is equally off-putting since it masks the meaning.

Balancing Complexity, Focus, Interest and Simplicity

Heavy style players usually use very clean pickups – such as EMGs, Dimarzios or similar – because they have a more focused, simpler sound which will respond well to plenty of complex distortion. Blues players on the other hand, will choose a more complex sounding pickup – with plenty of harmonic content and a characterful EQ curve – but have their amps at much lower gain settings, which allows the tone to retain some focus.

Few people choose to use pickups like EMGs for 100% clean tones since the simplistic tone is uninteresting and often described as sounding ‘sterile’. Similarly, few people match a complex sounding pickup like a P-90, with high gain amplifiers, since this usually just results in ‘mush’.

Of course, so far the concepts of complexity, focus, interest and simplicity, are over simplified (ha ha) – but read on through the coming series and you’ll get a better idea of what I mean.

Frequency Response

The guitar is a mid-range instrument, which is the most sensitive part of human hearing – so it is little wonder that we guitarists are so fussy with our tone. The guitar itself (i.e. the wood) resonates strongest in the mid frequencies, also the pickups have an electrical resonance that emphasises the mid frequencies even more. Generally speaking, humbuckers will have a stronger mid-emphasis than single coils.

In contrast, guitar amplifiers are very lacking in the mids – guitar amplifiers are ‘scooped’. This is one of the reasons why electric-acoustic guitars sound so unnatural when amplified through conventional guitar amps (electric-acoustic guitars require specific ‘acoustic’ amps). Turning the ‘high’ and ‘bass’ knobs all the way down, and the ‘mid’ knob all the way up, will give you a fairly ‘flat’ response and a rough impression of the actual guitar sound without the mid scoop of the amp.

The last aspect of a basic lead setup is the speaker cone(s). These typically have very limited upper frequency response. Amp cabinets with ‘full-range’ speaker systems would sound incredibly harsh and/or fizzy, so guitar speakers are deliberately made to be ‘lo-fi’ (low-fidelity).

These various cuts and boosts at different frequency areas can all affect the final guitar tone in good and bad ways. Swapping in a wider-bandwidth speaker, for instance, may increase clarity and ‘bite’ but could also increase harshness and fizz. Dropping the mids on the tone-stack might ‘smooth’ out the sound, but could also cause your tone to lose its impact, power or ‘balls’.

Distortion

The three parts of the signal chain described above (guitar/pickups, amplifier, speakers) also introduce harmonic distortion. Usually just called distortion, or overdrive, harmonic distortion is a non-linear compression of an audio signal. This means distortion introduces overtones/harmonics into the signal that were not already there. In short, pickups, amplifiers and speakers add upper frequency content to the signal.

It is important to understand that this is not the same as simply boosting the higher frequencies, such as turning up the ‘high’ knob on the tone controls. This is not boosting audio that was already present in the signal, but is actually changing (i.e. distorting) the signal so that the audio coming out is harmonically different from the audio that went in.

Although everybody is familiar with the distortion available with the ‘gain’ knob on the amp, many people don’t realise that pickups and speakers distort as well. Wide-bandwidth pickups (such as active pickups) sound very clean (some people even describe them as ‘sterile’). By contrast, a P-90 will have a much more complex tone, partly as a result of extra harmonic content. Also, a P-90 has a far more ‘middy’ and ‘peaky’ response while an active pickup has a much flatter response, so this also contributes to the sonic differences between the two.

Also, it is common for people to talk about pickups as being ‘dynamic’ or ‘compressed’. It is usually the case that the more ‘compressed’ the pickup is, the more distortion it introduces. Similarly, a more ‘open’ or dynamic pickup will usually impart less distortion.

Speakers also distort, especially when driven hard. Usually this means very high volumes, though guitar speaker manufacturers may deliberately make speakers which will distort at lower volumes.

Basic guitar tone is a result of controlling distortion and controlling the overall frequency response of the signal along the chain.

But What If I Don’t Use Distortion?

Even guitarists who play with a ‘clean’ sound usually have some distortion – it’s just very subtle, and often imperceptible. It is usually a subtle, controlled use of distortion that makes a clean sparkly tone, rich and complex rather than dull, lifeless and sterile. Remember, harmonic distortion is simply harmonic content that was not originally present in the signal. That does not mean that distortion needs to be ‘in-your-face-high-gain’ type distortion. You can use subtle distortion to ‘warm up’ and thicken’ clean sounds too.

In ‘Lead Guitar Tone Part 2′ I’ll mostly be discussing the non-subtle type of distorted lead sounds, but in ‘Lead Guitar Tone Part 3′ I’ll talk about the subtler kinds of distortion that clean players can make use of too.

Attack Characteristics and Compression

Along with distortion and frequency response, the attack characteristic (aka ADSR envelope) is another key factor in how we perceive a guitar’s tone. Depending on the listener/player, the attack characteristic can be a subtle after-thought, or an integral key to the person’s tone.

For guitarists, the attack characteristic is probably best described by how well a sound ‘jumps’ out of the speakers. The key to achieving a highly dynamic sound is to use very dynamic (open) pickups. Looking around online forums etc, I’ve found that most guitarists seem to prefer a highly-dynamic pickup. Open pickups will respond well to playing dynamics – stronger pick attack can drive an amp into a smooth overdrive, whilst a lighter touch can clean up well for rhythm sections. The downside to highly dynamic pickups is that, with a medium overdrive setting, the attack will likely be significantly more distorted than the sustained part of the note. Also, distortion compresses most of the dynamics out of a tone, so dynamic pickups will be of little advantage to a high-gain player. Generally speaking then, you are going to get the most benefit from pickups with a wide dynamic range, if you are using clean(er) tones.

Closely related to attack characteristics is the issue of compression. Compression is anything which serves to reduce the dynamic range of the final signal. This can include heavier strings, higher-output pickups, amplifier overdrive, distortion from pedals, heavy speaker materials, and of course dedicated compressor pedals.

The benefit of signal compression is that it raises the average level of the signal, and can also increase the perceived level of the signal as well. This means that compression makes your tone seem louder! Unfortunately, because compression is effectively reducing the dynamic range of the signal, it has the significant drawback of reducing the expressivity and musicality that can be achieved with sensitive and dynamic playing.

Controlling/manipulating the compression and attack characteristics of your final tone is something that you should do as a final touch on an already stellar tone. In a recording environment, this would mean doing it ‘in the mix’ after you’ve recorded the uncompressed guitar tone. Essentially altering the attack, or adding compression, has the potential to increase the immediacy and impact of the tone, but could also have the opposite effect of robbing the tone of its expressive potential. I’ll talk more about compression and attack in another post in this series, with some specific tips, tricks, dos and don’ts.

Summary

Controlling basic tone comes down to knowing:

1. How much distortion – high gain or low gain
2. What kind of distortion – symmetric or asymmetric
3. Where in the signal chain the distortion occurs – at the pickups, the amp, the speaker or a combination of all three
4. Which frequencies are distorted the most – distortion voicing
5. Which frequencies are dominant
6. Which frequencies are subdued
7. Attack characteristics
8. Dynamic range

P.S. Intermodulation Distortion

Before we finish up, I need to make a quick note about ‘intermodulation distortion’. This is the main distortion that we don’t want. Intermodulation distortion is the effect where signals at different frequencies combine to create signals at other, musically unrelated, frequencies.

Harmonic distortion (the good distortion) creates frequencies which we perceive as being musically related, and are pleasing to the ear (the frequencies conform to the harmonic series). However, the extra frequencies that occur in intermodulation distortion are not based on the harmonic series, and the human ear perceives it as sounding out-of-key.

The greater number of frequencies that occur simultaneously, the greater chance of noticeable intermodulation distortion. Meaning that harmonically complex signals produce stronger intermodulation distortion. Overdrive, fuzz, and ‘distortion’ pedals create their effect by increasing the harmonic content of the signal, so these pedals all increase the likelihood of objectionable intermodulation distortion. Amplifier distortion, compression, speaker distortion and virtually any kind of signal processing (such as reverb or delay) can also lead to an increase in apparent intermodulation distortion.

So, for now, the rule of thumb is to keep your distortion levels down as much as you can get away with (actually that’s good advice for other reasons too which we will soon discover). Later on, though, we’ll look at other ways of combating intermodulation distortion.