Vibrato (Italian, from past participle of "vibrare", to vibrate) is a musical effect consisting of a regular, pulsating change of pitch. It is used to add expression to vocal and instrumental music. Vibrato is typically characterized in terms of two factors: the amount of pitch variation ("extent of vibrato") and the speed with which the pitch is varied ("rate of vibrato").
In singing, it can occur spontaneously through variations in the larynx. The vibrato of a string instrument and wind instrument is an imitation of that vocal function. Vibrato can also be reproduced mechanically (Leslie speaker) or electronically as an audio effect close to chorus.
Terminology
History
Descriptions of what would now be characterised as vibrato go back to the 16th century. However, no evidence exists of authors using the term vibrato before the 19th century. Instead, authors used various descriptive terms interchangeably, including tremolo, bebung, or tremblement, or descriptions such as wavering, shake or trillo. These “terminological uncertainties” continue to pervade modern definitions of vibrato.
Vibrato and tremolo
The terms vibrato and tremolo are sometimes used interchangeably, although (in the classical world) they are properly defined as separate effects. Vibrato is defined as a periodic variation in the pitch (frequency) of a musical note that is perceived as one fundamental frequency. Tremolo, on the other hand, is defined as a fast repetition of the same note (usually a semiquaver) or alternation between two notes, especially on instruments which do not have the ability of producing long sustained notes, such as the guitar (for instance tremolo picking).
Human perception
Presently, the leading understanding is that when vibrato is utilised, listeners are able to focus on the average pitch and hear it as a single fundamental as opposed to the alternation between two different fundamental frequencies. Carl Seashore (1967) conducted the first comprehensive studies on perceptions of vibrato in the context of classically trained singers, finding some individuals are 50-100 times more perceptive of the presence of vibrato than individuals with the least ability and that “much of the most beautiful vibrato is below the threshold for vibrato hearing and is perceived merely as tone quality.” This conclusion was confirmed by William Vennard (1967) who notes that the listener hears only the average pitch, and the fluctuation is interpreted by the as enhanced tonal quality.
In practice, it is difficult for a singer or musical instrument player to achieve only pitch vibrato (where only the pitch or only the volume is varied), and variations in both pitch and volume will often be achieved at the same time. Electronic manipulation or generation of signals makes it easier to achieve or demonstrate pure tremolo or vibrato. In the world of electric guitar and record production vibrato retains the same meaning as in the classical world (a periodic variation in pitch) but tremolo describes a periodic variation in volume usually achieved using outboard effects units.
Acoustic basis
The use of vibrato is intended to add warmth to a note. In the case of many string instruments the sound emitted is strongly directional, particularly at high frequencies, and the slight variations in pitch typical of vibrato playing can cause large changes in the directional patterns of the radiated sound. This can add a shimmer to the sound; with a well-made instrument it may also help a solo player to be heard more clearly when playing with a large orchestra.
This directional effect is intended to interact with the room acoustics to add interest to the sound, in much the same way as an acoustic guitarist may swing the box around on a final sustain, or the rotating baffle of a Leslie speaker will spin the sound around the room.
Typical extent of vibrato
The extent of the variation in pitch during vibrato is controlled by the performer. The extent of vibrato for solo singers is usually less than a semitone (100 cents) either side of the note, while singers in a choir typically use narrower vibrato with an extent of less than a tenth of a semitone (10 cents) either side. Wind and bowed instruments generally use vibratos with an extent of less than half a semitone either side.