Vibrato unit.html

A vibrato unit is an effects unit used to modify the sound of an electric guitar by producing a regular variation in the amplitude (volume) of the sound. In all other contexts this effect is known as tremolo rather than vibrato. The only guitar amps that featured true pitch shifting vibrato were certain models offered in the late 50s and into the 60s by Magnatone.

The vibrato/reverb channel of a Fender Vibrolux amplifier.
The potentiometers, from left to right, read Volume, Treble, Bass, Reverb, Speed and Intensity.

Vibrato units may be individual stomp boxes or built in to multi-effects units, but are traditionally built in to guitar amplifiers. They are particularly used in surf music. A vibrato unit normally has three controls:

Speed controls the frequency of the variation, typically from a maximum (fully clockwise) of five to ten hertz to a minimum which may be as slow as one cycle taking several seconds.
Depth or intensity controls the amplitude (volume) of the variation. The minimum depth (fully anticlockwise) is typically (but not always) zero, that is no effect on the sound at all; The maximum depth does not normally cut the sound off completely at the cycle minimum, but may reduce it by as much as 6dB, virtually a cut off to the ear.
An on/off control, traditionally a pull-on switch on the depth potentiometer, a foot switch, or both. The off position bypasses the unit. In the case of an amplifier mounted unit where both switches are supplied, the unit is bypassed if the pull-on switch is off, regardless of the pedal. If the pedal is not plugged in, the unit is turned on and off by the pull-on switch; If the pedal is plugged in, then it controls the unit when the pull-on switch is on.

Vibrato or tremolo?

The term vibrato unit was introduced on high-end Fender guitar amplifiers in the 1950s, in the same period in which what is now called a tremolo arm was introduced on Fender guitars.

There has been much speculation as to why Leo Fender chose to call it a vibrato unit, while he called a device that produced true vibrato a synchronised tremolo, in both cases reversing the established usage. The synchronised tremolo was introduced in 1954 on the first Stratocaster guitar. The only previously successful tremolo arm was the Bigsby vibrato tailpiece, often simply called a Bigsby. In 1958, Fender reinforced his usage with the Fender floating tremolo on the Jazzmaster and some subsequent guitars. The synchronised tremolo became the most copied of these three basic patterns of tremolo arm, although both of the others continue to have some following. Similarly, many other amplifier makers introduced vibrato units producing similar effects to the Fender units. Some of these makers, including Gibson and Ampeg, referred to their volume-modulation effects as tremolo.

Although the Fender corporation called some of their later tremolo arm designs vibrato tailpieces (see tremolo arm for details), both the terms tremolo arm and vibrato unit became established, with the result that electric guitarists traditionally use the terms vibrato and tremolo in the opposite senses to all other musicians when describing these hardware devices and the effects they produce. From time to time it is proposed that this should be corrected, and the term tremolo arm rejected in place of a neutral term such as whammy bar, but there is no corresponding "correct" term for a vibrato unit.

The task of producing a similarly correct term for a traditional vibrato unit is slightly complicated by two factors:

The subsequent development of other guitar effects units such as chorus effects, phasers (sometimes called phase vibrato units) and flangers, which can be set to produce changes in pitch similar to traditional vibrato as understood by most musicians.

The fact that, under harmonic analysis and contrary to the expectations of many musicians, the output of the original vibrato unit does contain other frequencies near that of the note frequencies and in place of the note frequencies. These are the mathematical result of the variation in volume of the notes, so there is a slight sense in which Leo Fender was correct in his naming of the vibrato unit (but not of the tremolo arm).

Guitarists do also use "true" vibrato, in at least three ways:

As finger vibrato similar to that produced by movement of the left hand on the violin and other stringed instruments.
By use of the tremolo arm provided (by whatever name) on many electric guitars.
By manipulating the tailpiece of an archtop guitar not fitted with a tremolo arm, normally with the right hand. This is particularly a jazz and blues technique.

In common with all other musicians, all guitarists from classical to rock use the term vibrato to describe finger vibrato.

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Vibrato or Tremolo?