Geek Speak: All About Distortion

I occasionally muse on the fun we electric instrumentalists get to have compared to the typical acoustic musician. Sure, we can benefit equally from the personally rewarding thrill of playing music, but we have a leg up when it comes to mangling, modifying, and extracting unholy rackets from our instruments.
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I occasionally muse on the fun we electric instrumentalists get to have compared to the typical acoustic musician. Sure, we can benefit equally from the personally rewarding thrill of playing music, but we have a leg up when it comes to mangling, modifying, and extracting unholy rackets from our instruments. It’s fun of a kind that the average bassoonist or saxophonist can’t touch, and though some intrepid acoustic musicians integrate electronics into their sound, it’s generally the purvey of us electricity-dependent players. The conversion of the acoustic energy of a vibrating string into a corresponding electric signal is the key to a universe of sonic manipulation, as electrical signals are easily altered through relatively simple circuits.

Over the coming months, I’ll focus on broad categories of effects, diving deep into the technology behind the sounds. Understanding effects will not only make you a smarter consumer, it’ll bring efficiency to your hunt for idealized tones. This time, we’ll explore that most ubiquitous of effects: distortion.

First, a vocabulary lesson. Distortion effects may be cloaked under the guise of a number of other names, each of which suggests something of the distortion’s character. “Overdrive” effects are usually intended to emulate the sound of a tube amp driven hard. “Fuzz” pedals tend to sound edgy and nasty, in a good way. Plain old “distortion” pedals can vary widely, offering everything from subtlety to speaker-shredding insanity. In short, it’s all distortion, but in different flavors.

All distortion acts on the same basic principle: adding harmonic content by “clipping” the audio signal. The result is a lower-fidelity version of the sound, although it’s lo-fi in a stylistically pleasing way. The term “clipping” comes from a distortion’s influence on the waveform of the input signal. Distortion effects essentially chop off the peaks and valleys from the waveform, and in doing so, introduce frequencies to the content that weren’t there before. Distortions also amplify the signal, changing the slope of the wave as it reaches its momentary maximum. The resulting waveform starts to sound more like a square wave, a waveform notable for its buzzy, slightly hollow sound.

When a distortion performs its clipping function, it’s working on a signal that’s already rich in harmonic content—the output of your bass. No matter the distortion circuit, the added harmonic content will have some relationship to your notes’ fundamental frequencies, meaning it will emphasize particular “overtones” of the fundamental. The components of the circuit determine the extent to which certain parts of a signal’s harmonic spectrum are manipulated. This is why different distortion effects have different personalities.

In a typical distortion pedal, a small high-gain integrated circuit, called an op-amp, is used in conjunction with one or more diodes, here used to perform the clipping function. By ingeniously combining these basic electrical components, a host of distinctive distortion effects are available. Some distortion effects also utilize field-effect transistors (FETs), a type of transistor often said to more accurately emulate the smooth, harmonically consonant distortion of an overdriven tube amp.

The reason behind the glut of distortion pedals on the market is that there are many ways to skin this particular cat. An engineer can alter the type of diode (choosing, for example, between silicon and germanium designs), offer EQ to further sculpt an output signal’s frequency response, or design a circuit that affects the alternating wave of a bass asymmetrically, with a variety of sonic results.

Whatever your preferred flavor, distortion is a potent effect when used appropriately. Perhaps most important to bear in mind is that since distortions introduce new harmonic content, manipulating the frequency response of your bass before it hits the distortion can dramatically alter its sound. Similarly, the harmonically beefy output of a distortion will produce markedly different results in other effects down the signal chain.

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