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How Guitar Pedals Work

How guitar pedals work is an age-old question for musicians…

I can say with complete honesty that when I was first into guitar effects as a teenager, I had absolutely no idea how those pedals worked except that you plug a guitar into one side and the other side into your amplifier, make sure there’s battery power, or a power adapter, and as if by magic, your guitar sounds different. Well, to be a little more honest than that, it took no time to figure out a distortion pedal feeds power into a circuit or component that can’t handle that power level, and this takes the peaks and troughs off the sound wave so as to create a whole new sound. I could imagine a flanger was an extra fast echo with a changing delay time because a guy showed me the pitch-shifting effect of changing the delay time on a digital delay. Phasers had me stumped, though. Compressors were explained neatly by someone else and there was no problem understanding them.

Is this article about me? No it isn’t.

One thing you find a lot of among guitar pedal manufacturers is an ongoing commitment to making the perfect overdrive or distortion for every occasion. This is good. Who want’s to buy a new amplifier to crank up for every creative angle you want to experiment with? Not for me. There are pedals what will give you that specific crunch or saturation or explosive power you need, whatever you have in mind, and it is literally just a matter of searching, or chaining pedals together. You may have an overdrive pedal which comes close to what you want and you can chain it in serial after a parametric equaliser, graphic equaliser and/or compressor. Sometimes extra depth can be obtained if you place an octave pedal before the overdrive too. You could also place another drive or distortion pedal afterward so as to flavour your offering.

Overdrive and distortion are basically the same thing with the main difference being how intense the effect is. On a technical basis, the difference is more than the power level fed into the dinky little circuit that’s fighting a losing battle. It’s got to do with whether the tone, at whatever level of driving, is more suitable for heavy metal or pop – to put it one way. The methods used by manufacturers are proprietary and probably as myriad as the grains of sand in an Old Testament desert. Code for saying let’s not get too involved in how it’s done. Aurally, it’s a matter of saturation through to grit and gravel in an overdriven tone, and violent thoughts through to intensity personified in the form of something vile in a distorted tone.

As indicated above, frequency filtering and compression coming into the drive/distortion circuit can give you a decisive influence on how the overall sound is. But then you have the question of how the drive/distortion circuit works. If it’s simply a matter of clipping the peaks and troughs of the waveform, then you can end up with a very rough and dirty output. A given thickness of wire of a material with given conductivity can transfer only a certain number of electrons at any point in its length simultaneously. Any excess is resisted and dissipated as heat. When this is happening you get clipping, with flat tops and bottoms imposed over the waveform. As a string vibrates its frequency content modulates and phases slightly, the sustain phase of the note, which in a clean signal sounds alive and present, can sound fluffy and unstable in a signal that is distorted with nothing more to improve it. (note that in a complete mix there is a lot of other sound to distract from it, so guitarists get away with murder). Clever electronics can minimise the farting and buzzing and render a more pleasing, consistent tone. For that reason, it can be worthwhile hunting for a pedal that does exactly what you want.

If a drive or distortion circuit is doing its job well, the result is not  merely to affect peaks and troughs in the wave, but all power levels of the waveform. This is mimicked digitally with a simple algorithm called waveshaping. You bend the whole wave so that it develops new tonality. In a typical application the end result is a wave with fatter, rounder tops and bottoms and which is steeper around the zero baseline. Sonically you go from a richer, more present clean tone through to a proper hard rock sound by simply adjusting the amount of rounding which occurs. But the sizzle and power of a heavy metal sound is better attained digitally with a washaping algorithm that has a more angular, stepped or jagged shape. Wild reversals in the way voltage levels (or sample values) are multiplied or divided creates strong, treble inharmonic sound components that create the sizzling effect. Signal components that are very quiet can be amplified to the top of the dynamic range while what was louder before is forced to compete. This might sound like a description of heavy compression, but the difference is that here we are transmogrifying the wafeform rather than merely adjusting the volume. Whether analog circuitry or digital waveshaping, the effect on the waveform is the same.

Experience shows that you do not need to spend big on up-market equipment to get a great sound. I once had a 10 watt bargain basement practice amp which I used with a Boss compression sustainer and a Boss digital delay and I used the amplifier’s pre-amp to get a little dirt after the pedals and got a really great sound worthy of a much costlier rig – possibly the peculiarities of the guitar I was using had something to do with it. This was weekly, live in a church band, for a year or more. Conversely there are brands of pedals which cost as much for an ordinary overdrive as you would spend on an up-market big-brand guitar. It is the literal truth that you can have a budget priced pedal that gives you a sound comparable for all intents and purposes to a large, multi-kilogram valve amplifier, and pedals which mimic the clean sounds of specific amplifiers. It pays in no uncertain terms to shop around. If you cannot try out pedals in store, or are too shy to frustrate sales staff with studious try-outs, then look up the review videos you find through search engines.

Another very important part of the contemporary rock guitar performance is the reverberation you are using. Let’s have a look at reverb effects pedals and how they work. Until the advent of the electronic echo effect it was necessary to use physical equipment – that is, solid objects, chambers and tape loops – to get reverb effects. The history to this is amazing for audiophiles. There was the echo chamber in which highly reflective walls, floor and ceiling would reflect sounds with microphones and a speaker placed wherever it seemed suitable, just to record the effect. Theatres could be used for this too. You can imagine the cost involved in just getting a nice sound. The most famous example is Phil Spector’s “Wall of Sound” effect which involved all the musicians in a performance together in a reverberant room with each microphone picking up not only the instrument but the entire room effect and every other instrument at once – all with different delays due to the distance from one performer to all others. It was a sonic beautiful mess. Audio tape machines with a feedback lead placed between playback and record heads could provide an echo effect that sounded more like science fiction – hence their frequent application in sound effects in vintage sci-fi shows – although multiple tape echoes could have provided for a much cheaper reverb sufficient to pretty-up a sound. Then there was the reverb plate. Now we are talking. A metal sheet thin enough to really shimmer and suspended rather than held on anything solid, could – actually can – be stimulated with an electromagnet like in a common speaker, so as to vibrate it in accordance with a musical performance. The sheet then echoes the sound in multiple reflective waves within its own structure, creating a highly diffuse reverberation effect. Spring reverbs in amplifiers are a poor man’s version of the reverb plate. They are good enough for all intents and purposes of a guitarist as part of a band, and due to their commonality have carved out a market of their own. The tell-tale wobbling resonance of a spring vibrating to an audio signal and transferring to a transducer is sought after because it was used a lot in old days when modern music was being defined. It is good, though. Nothing like it.

Reverberation is the coincidence of soundwaves being repeated over and over at different rates simultaneously. When we hear this coming into both ears in different patterns, we perceive that there is a material space around us of a certain size and shape and material. The detail of our perception is a result of the delay in each individual echo, the frequency response of the echoes, the change in time of the overall frequency content, any resonant frequencies that appear, the dominance and timing of any stand-out echo pattern, whether there is a metallic or smooth quality, and the complexity of diffusion in the echoes. We feel our way acoustically around physical spaces even without sight or touch.

Since the advent of digital delay (as opposed to the circuit complexities of analog delay), we have tried to mimic real-world physical echoes with clever algorithms. I have done this myself when I was involved heavily in digital signal processing. The first bounce-back is the “early reflection” stage of a reverb. This is done with parallel regenerations called “finite impulse response” (FIR). They are quick, creating a static phasing effect known as comb filtering. Each regeneration, repeated programmatically at decreasing levels until there is no audible regeneration left, phases against each other to alter the sound wave and amplify some frequency components while diminishing others due to phase interaction. You get remarkably different tones as a result which suggest to our subconscious minds that we are hearing the musical performance in different acoustic spaces. We automatically perceive different building materials or natural environments with whatever natural objects around about. Flavouring the sound like this is the role of early reflection. It is possible, even, to create impressions of natural environments that we have never experienced. To give an example, I once created a reverb to mimic the middle of a highly reflective sphere and it sounded perfectly real with headphones on.

Naturally, as early reflection decays, you get the rise of distant reflections. These are achieved with the use of longer-delayed feedback echoes in series. The property of feedback is also termed “infinite impulse response” (IIR) and provides for an echo that deteriorates until the medium can no longer sustain it, just as in the physical reverb devices described above. Because they are in series, they also create new echoes with faster rates between themselves. This mimics the real-world characteristic of sounds echoing, not in straight lines, but in radial fashion, off whatever object is nearby. Thus, a natural reverb becomes more diffuse in time. Every object absorbs sound as well as reflecting it, and most absorb high frequencies more efficiently. Therefore, a natural reverb decays and becomes mellower in time. (Concrete is an exception, reflecting higher frequencies better than lower ones). The increasing absorption of high frequencies can be achieved in a digital system by using simple FIR filtering in the IIR part of the system, while the overall tonality is determined earlier in the FIR stage.

These days there are reverb effects that include modulation. Remember above I said I was shown this when a shop owner was showing off a digital delay to me as a kid. You can get some effects reminiscent of a cave full of lapping water and some other really fantastical environments with modulating reverbs. It’s really worth experimenting because your audience could be really impressed with a lead break that suggests weird and wonderful places to them and takes them somewhere they haven’t been before. Nice thought – although doing this earlier in the evening when no-one is too drunk or stoned might help.

 

Good luck on your hunt.

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