Saturday, September 13, 2008

Guitar Distortion And Compression: Everything You Ever Needed to Know About Guitar Pt. II

Distortion And Compression

When you are talking about sound, "compression" refers to the reduction of dynamic range. This can mean making loud sounds softer, soft sounds louder or both. It is used extensively in recording, broadcast, live performance and is even built into some amplifiers to help control sudden volume spikes.

Distorted guitar is most associated with rock music but it turns up elsewhere as well. Country and jazz guitarists along with those playing other styles of music found around the world have found the fun in tube overdrive and other types of distortion. Still, even people who use it may not know what is actually going on when a guitarist uses a distortion pedal or dials up an overdriven sound on their amp.

It is sort of a shame we call this "distortion," a word that simply means to change something from its original or intended form. The distortion used with guitars is relatively specific, although it comes in many sonic flavors and is generated in several different ways. Guitar distortion has its roots in turning an instrument amplifier up "too loud." In this case "too loud" means louder than the amplifier can do cleanly--without distorting the sound.

The effect is essentially the same as turning up a clock radio or boom box all the way. The amplifier in the radio is intended to take the radio station's signal and make it louder, but otherwise preserve the sound's integrity. At a certain point it will run out of power and no longer be able to faithfully reproduce the signal at any higher volume. Past that point the amplifier in the radio will do what it can but the peaks of the signal will not go as high as they should. This is called clipping.

The result is a signal that doesn't get any louder itself, but has overtones added to it in stead. Those overtones are the "fuzz," "buzz" and gravelly qualities of distorted instruments. If you were to look at the waveforms a clean sound would look rounder and a clipped version of the same sound more square. Anyone familiar with synthesis will know that a rounder signal more nearly approaches the purity of a sine wave while the clipped signal approaches the extensive overtones found in a square wave.

This also has implications for mixing. Distortion adds high pitches to the original signal. No matter how low of a not a guitarist plays the overtones added by distortion can, theoretically, go infinitely high. This means that while a clean guitar part may mostly stay out of the way of a high keyboard part a heavily distorted guitar may turn into a problem, even if the guitarist does not play aggressively.

There are a few things about distortion that attract guitarists and listeners. First, it opens up a vast range of tonal qualities and other variations of the guitar's sound. It also provides compression.

By cutting the tops off of the waves making up the guitar's signal distortion throttles the signal, reducing it's dynamic range. Reducing dynamic range is the very definition of audio compression. Invariably the entire signal then gets amplified, resulting in the quieter parts of the sound being louder than they would have been with out the distortion/compression.

Guitarists don't necessarily think about it, but this is part of what they like about distortion. The western human ear is quite accustomed to compression on everything from radio announcer's voices to drum tracks. Basically, we like it because it makes things easier to hear. For guitarists it also makes certain things possible. Some techniques such as pick harmonics are much more workable with compression, whether in the form of distortion or a pure compression effect.

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