Electric Guitar Effects

Electric guitars are most often made with solid bodies since they depend upon electromagnetic pickups and amplifiers to produce the sound and are not dependent upon the resonance of the hollow body like the acoustic guitar.

The fact that the output is electrical has made possible a dizzying array of sounds produced by electrically and electronically modifying this electrical output. Besides the volume and tone controls on the guitar and on the amplifier, a variety of outboard devices are used to obtain custom sounds and effects. As an attempt to organize these effects, consider the following classifications:

Signal Reshaping

• Distortion and overdrive: In the early days of electronic music, vacuum tube amplifiers were used for processing the output electrical signals. Like any amplifier, these tube amplifiers had a maximum amplification above which they began to clip the peaks of the waveforms. While the resulting distortion may have disturbed the electrical engineers, a substantial fraction of the musicians liked the distorted sound and it became part of the musical medium.

  Now, in the days of solid state signal processing, outboard units are available to produce a facsimile of the old tube-type distortion. Some units actually incorporate a vacuum tube and do it the old way. Other electronics packages simulate the effect. The "tube-type" distortion is preferrable to many over the kind of distortion produced by solid-state amplifiers because the tubes just gradually rounded over the peaks as they went into distortion, whereas the solid state devices just chop off the tops of the peaks cleanly at the supply voltage point, producing a harsh distortion. One type of distortion device, employed as a distortion pedal, was called a "fuzz box".

• Compression: A "limiter" is envisioned as a circuit which prevents the output signal from exceeding a certain limit. If it did this by clipping, it would cause distortion, but if it can do it cleanly by just progressively reducing the amplification of the incoming signal, then it may properly be called a compressor. A compressor reduces the overall dynamic range by "compressing" the gain of high amplitude signals while maintaining the design gain for lower amplitude signals.

  Compressors are available as footpedal controls and can be used as an effect on electric guitar signals, for example. They can be used to obtain greater sustain for a string by setting the gain high and allowing the compressor to keep the output signal at a more-or-less constant level until the natural sustain of the string drops the signal below a certain threshold.

• Ring modulation: In the context of signal reshaping, the ring modulator takes the signal from the instrument and adds a second signal from a local oscillator or signal source. The two signals are combined to produce the sum and difference frequencies, which are then the output of the device. This scheme was used in the electronic music of the 1950's. The output frequencies track the input signal frequencies, but do not equal them, so there is a shift from the original pitches. The ring modulator has been produced as a footpedal, and ring modulator type effects are included in some modern electronic effects boxes.

• Pitch Shifters: Microprocessor-based devices can take the signal from a guitar and shift its frequency base. This amounts to sampling the sound and reconstructing it at a different frequency, so a lot of computation is involved. These devices range from note-shifting foot-pedals to studio-based harmonizers.

Signal Augmentation

• Flanging: This effect involves mixing two copies of the same signal with one of them slightly phase shifted. Historically, it had its origin with studio engineers using reeel-to-reel tape recorders. They would make a copy of a tape and then feed the original and copy together to a recorder, having placed a pencil on the flange of one tape to slightly alter its speed. The slight speed change would not be enough to cause notable delay, but would be enough to cause the two waves to be "out of phase" with each other. The effect is described as a king of "swirling" sound, with notable pitch oscillations if it became more extreme.

• Phasing: Similar to flanging, but without the frequency shifts. Produces a similar "swirling" sound.
• Chorus: Splitting the two signals further apart so that they are over a cycle apart in phase allows you to perceive two distinct signals, like two voices together. Called "chorus", this effect is perceived as less pronounced than flanging and phasing. It is described as producing a "thickening" of the sound, like reverb.
• Reverb: Adding back in copies of the original signal with time delays so short they cannot be perceived separately.
• Delay and Echo: Adding back in one or more copies with enough delay that they are distinguishable. This was sometimes done with tape loops, so that sounds would be heard repeated a number of times. Digital delay has made possible much more flexible delay and echo effects.

The Fuzz Box

A guitar effect which falls under the heading of distortion is the "fuzz box". This device uses a square wave generator in the form of a Schmitt trigger to introduce a variable frequency square wave to accompany or even replace the original signal. The proportion of clean to distorted signal can be adjusted as well as the combined gain.