Sound effects occur in nature every day, all around us. Musical effects are an attempt to manipulate sounds from an instrument in order to recreate – you guessed it – natural sounds. This Audio Guide is a basic overview of the 'Science of Sound' as it relates to music, particularly with the usage of guitar effects. The audio players below each description contain examples; turn up the volume and click to listen. We hope this serves as a useful tool as you explore what your guitar is capable of. Scroll down to enjoy this comprehensive guide.



When any system is driven beyond its normal operating range, it typically starts exhibiting negative side effects or consequences. For example, when a computer has too many applications open, it runs more slowly.

In the early days of the electric guitar before PAs were loud enough to ensure that every member of a band could be heard clearly, pioneers of the blues and rock and roll genres found that the overdriven sounds of their amps turned to loud volumes was actually very pleasing. What started out as necessity because of poor live sound reinforcement during live performances ended up being a stylistic and aesthetic choice. Today, an overdriven sound is synonymous with rock and blues. Effects builders are making fantastic pedals to achieve the sound of a tube amp cranked, without actually having to actually turn up too much.



The word distortion has a negative connotation which can imply that what one is experiencing is a warped, misshapen, deformed and possibly misleading version of the original. For example, a distorted picture might be out of focus or not have the same color balance as reality. In the world of guitar effects however, the word distortion can have a very positive connotation and this "altered version of the original" is often sought after.

Distortion occurs when a signal is overdriven to the point that the peaks of the signal waveform are "clipped". If you were to look at visual representations of a clean sound wave and a distorted sound wave, the clean one would have smooth peaks and valleys, whereas the distorted ones would look as if someone took scissors and "clipped" the tops and bottoms off. This clipping is what makes the sound "fuzzy" or "dirty". Different circuit designs can clip the signal more or less aggressively; the more aggressive the clipping and closer to a square wave it becomes, the more the signal distorts.



Fuzz is the most extreme form of distortion which essentially clips off so much of the wave form that it starts to approximate square waves. This form of clipping is so extreme that the sounds coming out of these pedals often have many additional artifacts such as high noise floor, self oscillating feedback, and a very accentuated harmonic content.




As the name implies, a compressor simply reduces the volume of loud notes. This gives the impression that softer notes are equally loud, effectively compressing the dynamic range of a signal. We actually use this effect every day, since our ear has a built-in compression system that protects us from loud noises and allows us to hone in on softer ones.

In the world of guitars, a pedal that makes your loud notes softer, but doesn't affect your soft notes very much, will essentially makes your playing sound a lot more consistent in volume. But as you can imagine, too much compression can also kill the expressiveness of your playing by reducing the dynamic range too much. Since a compressor is lowering the loud parts of a signal, it can actually even out the 'envelope' of a sound, making its sustain and decay longer. Especially when used in conjunction with overdrive or distortions, compressor effects can increase the sustain of notes dramatically (sometimes infinitely).

The typical parameters associated with compression are Threshold (the input level at which the compressor will start working), Ratio (the multiple by which the incoming signal will be compressed once it passes the threshold), and Gain (since compressors reduce the loudness of peaks, most of them have the ability to "make up" some of the lost volume with post compression gain). On simpler compression pedals, manufacturers combine Threshold and Ratio on one knob which controls how much compression you get. Some more complex compressors have knobs that can affect how quickly the compressor kicks in (attack) and how long it will last (decay or sustain).

These more complex compressors can be set so that the attack and decay work in conjunction with the playing style to yield very specific results that have become staples in certain genres, such as "chicken picking" in Country music. 




Every sound has an attack, sustain and decay. If a sound is emanated in an environment that has reflective surfaces, such as hard walls, the early sonic reflections can build and bounce around for a discernible amount of time creating the illusion that the decay is longer than actual decay of the original sound. This physical phenomenon is called reverberation or reverb. Another term used to describe the elongation of the decay of a sound through reverb is the "tail" or "reverb tail" of a sound.

People have invented many ways to emulate this naturally occurring phenomenon in electro-mechanical mediums. Amongst the most common methods are plate reverbs and spring reverbs. In both of these examples, sound is introduced onto these mediums (free floating metal plate, suspended springs) and they then extend the "tail" of the sound by physically vibrating for longer periods of time than the natural decay of the sound that was introduced. In today's digital world, guitar pedals can emulate natural acoustical reverberation and/or its electro-mechanical counterparts with advanced DSP (digital signal processing).



Delay is one of the more recognizable naturally occurring sound effects; it's basically an echo. A delay pedal takes your incoming signal, records it into internal memory and plays it back at a later time. Typically, the user is allowed to adjust the number of playbacks, intervals between, and levels of the playback. The kind of internal memory will have a big impact on the sound of the resulting echo and how much it can be manipulated. This is why delays using magnetic tape (Fulltone Tube Tape Echo,) analog chips (MXR Carbon Copy,) and digital signal processing (Boss DD-3) have different sounds and limitations. 




In some ways, every instrument ever invented has always competed with and/or emulated the expressive nature or modulating quality of the human voice. One of the ways in which the human voice can be very expressive is through the use of vibrato, or the fluctuation or modulation of pitch while sustaining a note. Many instruments have the luxury of being more expressive in this way than others simply because of how they are built. Most stringed instruments for example, can achieve this by rapidly changing the angle or pressure of the finger, or by slightly bending the string up and down. In the case of woodwinds, reed or brass instruments, this fluctuation is caused by a modulation of air pressure or embouchure. In the case of electronic effects, a vibrato pedal takes an incoming signal and modulates the pitch up and down by a certain rate and depth. Typically, the parameters of rate and depth are variable and can be adjusted through knobs on the pedal.



Tremolo is very much like vibrato except it's a modulation of amplitude, or volume, instead of pitch. Unfortunately, because of their similarities, these terms are often confused to the point that incorrect usages are now part of our everyday vernacular. The whammy bar, or tremolo system, on a guitar for example is actually a vibrato system since it affects pitch, not volume. So essentially, a tremolo effect takes the incoming signal and makes its volume go up and down by a specific rate and depth. Typically, the parameters of rate and depth are variable and can be adjusted through knobs on the pedal. There are many great examples of tremolo out there, but two that illustrate it very clearly are the intro guitar parts to "Bones" by Radiohead, and "How Soon is Now" by The Smiths.



Rotary Speaker pedals are a digital or analog electronic emulation of a Leslie speaker cabinet. Leslie speakers were invented by Donald Leslie, who in the late 1930s, was trying to make his Hammond organ sound more like church pipe organs whose sound had a much wider spread and depth because they produced their signal from large vibrating pipes that were physically placed around and away from the player.

In some instances, such as in large churches, some of these pipes can actually be very far away from the player. Donald Leslie found that the best way to simulate this sensory stimulus in a more portable and confined package was to send the output signal of his Hammond organ to a speaker cabinet in which the speakers were actually physically rotating and hence "throwing" the sound around the room.

Among some other phenomena that our ears experience when listening to a Leslie speaker is the Doppler effect, which is that familiar "diving down" of the frequency of an ambulance as it drives by. This makes a lot of sense since the rotating speaker inside the cabinet is literally moving the sound toward and away from the listener. Although the Leslie speaker was originally created for the organ, guitarists have modified and adopted them through the decades. Today, there several iterations of rotating speaker cabinets that were designed for guitars and many more simulations in pedal form.

Because of Jimi Hendrix's heavy use, the Univibe is possibly the most collectible simulation of the Leslie speaker. A great example of an actual Leslie cabinet on guitars is George Harrison's guitar part on "Lucy in the Sky with Diamonds". A classic example of the Univibe on guitar is Jimi Hendrix's "Angel".


When a chorus of people sing the same note, not everyone sings the exact pitch at the exact time or with the same timbre. In the world of guitar effects, a chorus pedal works in the same way; it layers the incoming signal and delaying it slightly, creating fullness, and a sense of depth and dimension. Essentially, what you're hearing is the phase (or excursions of the waveform) of two or more signals slightly off time with each other. 



A flanger pedal takes your guitar signal and splits it into two. One original signal stays constant, while the second signal goes to a delay with increasing and decreasing delay time. Because the slight delay time on the second signal is changing at a periodic and consistent rate (something that typically does not happen in nature,) the result is a less "natural" sounding, or perhaps more exaggerated chorus.



Like chorusing and flanging, phasing occurs when one blends the original signal with one or more copies of this signal that have been modified so that the "phase" of the waveforms are slightly off from each other. A phaser is different from chorus and flanger because it is achieved specifically by running the affected signal through a modulating filter as opposed to a modulating delay. The result is still the same "comb filtering" effect through the spectrum of the sound, much like chorusing and flanging, but because the method is affecting the spectrum directly, the result is usually even more exaggerated or extreme than the other more tame effects.




In nature, when the frequency of a sound is doubled, the resulting pitch is an octave higher. For example, a 2 kHz tone is one octave above a 1 kHz tone and one octave below 4kHz. A more practical example in musical terms would be that if someone plays the A 440 Hz key on a piano and then plays the next A up on the keyboard, its frequency is 880 Hz. From a music composition standpoint, stacking octaves has been a very common way to "thicken" or extend the sonic timbre or quality of a musical moment. For example, having upright basses double the violin melodies in a classical piece or having a choir of women singing the same line as the men but an octave higher can have quite an impact. In the world of guitar effects, an octave pedal artificially generates an octave above or below the original incoming signal. There are pedals that can actually generate several octaves above and below the incoming signal. The result can be a thicker, harmonized sound. A very famous example of this is Jimi Hendrix's guitar solo in "Purple Haze". 



A pitch shifter pedal electronically or digitally modifies the incoming signal and creates pitches above or below the original signal and mixes both signals at the output. The result is very much like the description of the octave pedal above, except that instead of only being able to generate pitches that are exact multiples of the incoming frequency, pitch shifter pedals can generate other intervals, such as thirds and fifths. There are many modern digital effects systems that can generate almost any pitch desired above or below the incoming signal. There are even some systems that can "intelligently" discern if an interval above or below the incoming note is in the key of the song being played and modify it so that it is in key. There are many great examples of harmonized guitar solos that can be approximated with pitch shifter pedals from the early multitrack recording of Les Paul himself all the way to English Metal band Iron Maiden. 




An equalizer is a frequency dependent amplifier. In other words, EQ is an electrical device that can boost or cut the amplitude or volume of certain frequencies. There are many kinds of EQs, including (semi and fully) parametric, graphic, notch filters, band-pass filters etc. For the purpose of this explanation, we will only talk about graphic EQs – specifically a 6 band graphic EQ like the MXR M-109. These kinds of pedals have 6 levers labeled with different frequencies from low to hi (ie. 100 Hz, 200 Hz, 400 Hz, etc.) and these levers can be pushed up or down a certain range measured in decibels.

When the faders are pushed above the center (or unity gain), that frequency is boosted by however many dBs it's marked. If it is pulled below the unity gain line, that frequency is attenuated. For example, if one pushes the 100 Hz up to the 10db mark, pulls the 200 Hz down to the 6db mark, and pushes the 400 Hz lever to the 18 dB mark, then they are boosting 100 Hz by 10 db, cutting 200 Hz by 6db and boosting 400 Hz by 18 db.

A graphic EQ gets its name because by design, it graphically displays what it's doing to the sound on the front panel. For example, when you boost the lows, cut the mids, and boost the highs, the face of the EQ will look like it's got a smile. When someone refers to the sound of a guitar with the term "smily face EQ", this is what they mean. Strategically boosting or cutting frequencies on instruments can be a powerful tool for highlighting or blending certain sections like solos or accompaniment parts. 



A wah pedal effect is a narrow bandwidth filter whose frequency is variable and altered by a potentiometer that is physically attached to a lever or pedal. When the user pushes and pulls on the pedal or lever, the potentiometer "sweeps" the filter/eq through the range of frequencies varying the overall tone of the instrument. In other words, it's like running your instrument through an EQ through which you can control the frequency up and down with your foot while the boost is set pretty high (see EQ explanation above). Varying the tone in this way can give an instrument a human voice-like quality, almost as if the instrument is crying, hence the name. Two great examples showing very different techniques of this effect are the "Shaft Theme Song" by Isaac Hayes and Jimi Hendrix's "Voodoo Child".



In the world of sound, a filter is essentially an equalizer. Therefore, an envelope filter is an equalizer that varies and/or depends on the envelope of a sound to function. Every sound in nature has an envelope. The envelope of a sound is its attack, sustain and decay. The envelope of a snare drum for example is very different than the envelope of a flute. The snare has a sharp attack, short sustain and a decay that depends mostly on the room its in. On the other hand, a flute will have a much softer attack, a sustain that lasts as long as the player can hold their breath and a decay that depends on the reverberation of the room. An envelope filter reacts to the level of the incoming signal and applies an EQ curve only when the incoming level passes a threshold. Typically, that input threshold is variable (usually labeled "sensitivity") as well as the severity or depth of the filter applied. Some envelope filters have many other variable parameters, such as the attack and sustain of the filter (or how quickly the filter will start working and how long it will last), and frequency and bandwidth (how wide the range around the main frequency selected will be affected) of the filter that will be applied. The most common envelope filter is the "auto wah" which, as the name implies, is a wah effect that automatically turns on and off depending on how hard one plays. A great example of an envelope filter is the bass sound in Parliament's "P. Funk (Wants to Get Funked Up)". 



Ring modulation is achieved when the input signal is split, one of the signals is altered, and on the way out a new signal is artificially created out of the delta or differences of the two signals. This process can create "unmusical" byproducts and artifacts such as harmonic content that is inconsonant with the original sound. The result can be an unsettling or harsh sound that is hard to listen to. A very obvious and recognizable example of this effect on guitar is the opening guitars from Radiohead's "My Iron Lung" from The Bends.