The terms vibrato and tremolo are sometimes used interchangeably or inappropriately, although the strict definitions of each describe them as separate effects: vibrato is a periodic variation in the pitch (frequency) of a musical note, whereas tremolo usually refers to periodic variations in the volume (amplitude) of a musical note. In practice, it is difficult for a singer or musical instrument player to achieve a pure vibrato or tremolo (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 and/or vibrato.
There are some instances where one of the terms (vibrato, tremolo) is used to describe the effect normally associated with the other term. For example, vibrato is sometimes referred to as tremolo, notably in the context of a tremolo arm of an electric guitar, which produces variations of pitch. Conversely, the so-called vibrato unit built in to many guitar amplifiers produces what is known as tremolo in all other contexts. See vibrato unit for a detailed discussion of this terminology reversal.
The extent of the variation in pitch in instrumental vibrato is usually decided by the performer, but does not usually exceed a semitone either way from the note itself. Many string players vary the pitch from below, only up to the nominal note and not above it. The effect is intended to add warmth to a note, and in the case of bowed strings, adds a shimmer to the sound, as the sound pattern emitted by a well-made instrument virtually "points" in different directions with slight variations in pitch. This effect interacts 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.
Vibrato is sometimes thought of as an effect added onto the note itself, but in some cases it is so fully a part of the style of the music that it can be very difficult for some performers to play without it. The jazz tenor sax player Coleman Hawkins found he had this difficulty when requested to play a passage both with and without vibrato by the producer of a children's jazz album to demonstrate the difference between the two. Despite his otherwise exemplary technique, he was unable to play without vibrato. A symphony saxophonist was brought in to play the part.
Many classical musicians, especially singers and string players, have a similar problem. The violinist and teacher Leopold Auer, writing in his book Violin Playing as I Teach It (1920), advised violinists to practice playing completely without vibrato, and to stop playing for a few minutes as soon as they noticed themselves playing with vibrato in order for them to gain complete control over their technique.
The use of vibrato in classical music is a matter of some dispute. For much of the 20th century it was used almost continuously in the performance of pieces from all eras from the Baroque onwards, especially by singers and string players. A drastic change in approach cannot be understood wholly without regarding the rise of notionally historically accurate ("period") performance from the 1970s onwards. However, there is no actual proof that singers performed without vibrato in the baroque era. Vocal music of the renaissance is almost never sung with vibrato as a rule, and it seems unlikely it ever was. There are only a few texts from the period on vocal production, but they all condemn the use of vibrato.
Leopold Mozart's Versuch einer gründlichen Violinschule (1756) provides an indication of the state of vibrato in string playing at the end of the baroque period. In it, he concedes that "there are performers who tremble consistently on each note as if they had the permanent fever", but condemns the practice, suggesting instead that vibrato should be used only on sustained notes and at the ends of phrases. This however, does not give anything more than an indication of Mozart's own personal taste, based on the fact that he was an educated late Rococo/Classical composer. Although there is no aural proof, as audio recordings were not around for more than 150 years, that string players in Europe did not use vibrato, its overuse was almost universally condemned by the leading musical authorities of the day.
Vibrato was seen as an ornament, to be used sparingly. In wind playing too, it seems that vibrato in music up to the 19th century was seen as an ornament to be used selectively. Martin Agricola writing in his Musica instrumentalis deudch (1529) writes of vibrato in this way. Occasionally, composers up to the baroque period indicated vibrato with a wavy line in the sheet music, which strongly suggests it was not desired for the rest of the piece.
Music by late Romantic composers such as Richard Wagner and Johannes Brahms is now played with a fairly continuous vibrato. However, some musicians specialising in historically informed performances such as the conductor Roger Norrington argue that it is unlikely that Brahms, Wagner, and their contemporaries, would have expected it to be played in this way. This is a somewhat controversial view, although Arnold Schoenberg, a considerably later composer, seems to have disliked vibrato as well, likening it to the bleating of a goat. The curious idea that continuous vibrato was invented by Fritz Kreisler and some of his colleagues seems to be caused by the development of sound recordings which left some people with the impression that vibrato appeared but in the 20th century. However, the sources unanimously prove that Viennese early 19th century string players like Franz Clement and Joseph Mayseder were noted for their tasteful use of vibrato. These musicians (and the two Hellmesbergers) represent the school that Fritz Kreisler actually based his stylistic approach on.
The growth of vibrato in 20th century orchestral playing that has allegedly been traced by Norrington by studying early recordings, is not supported by actual samples. Norrington claims that vibrato in the earliest recordings is used only selectively, as an expressive device; the Berlin Philharmonic Orchestra were not recorded using vibrato comparable to modern vibrato until 1935, and the Vienna Philharmonic Orchestra not until 1940. French orchestras seem to have played with continuous vibrato somewhat earlier, from the 1920s.
It should be stressed in this connection that the sonic limitations of older recordings, particularly with respect to overtones and high frequency information, make an uncontroversial assessment of earlier playing techniques very difficult. In addition, a distinction needs to be made between the kind of vibrato used by a solo player, and the sectional vibrato of an entire string ensemble, which can't be heard as a uniform quantity as such. Rather, it manifests itself in terms of the warmth and amplitude of the sound produced, as opposed to a perceptible wavering of pitch. The fact that as early as the 1880s composers such as Richard Strauss (in his tone poems "Don Juan" and "Death and Transfiguration") as well as Camille Saint-Saëns (Symphony No. 3 "Organ") asked string players to perform certain passages "without expression" or "without nuance" strongly suggests the general use of vibrato within the orchestra as a matter of course.
Despite this, the use of indiscriminate vibrato in late Romantic music goes largely uncontested (although performances of Beethoven with limited vibrato are now not uncommon). Many people take the view that even though it may not be what the composer envisioned, vibrato adds an emotional depth which improves the sound of the music. Others feel that the leaner sound of vibratoless playing is preferable. In 20th century classical music, written at a time when the use of vibrato was widespread, there is sometimes a specific instruction not to use it (in some of the string quartets of Béla Bartók for example). Furthermore, some modern classical composers, especially minimalist composers, are against the use of vibrato at all times. In the 21st century some orchestras are now playing with noticeably less vibrato.
Not all instruments can produce vibrato, as some have fixed pitches which can not be varied by sufficiently small degrees. Most percussion instruments are examples of this, such as the piano.
The guqin, a Chinese bridgeless zither, has documents describing over 25 different types of vibrato that can be executed. Most peculiar is the vibrato ting yin (literally "still vibrato"); ancient manuals state that the finger on the left hand that is pressing the string should only move or rock ever so slightly so as to alter the pitch minutely, and some manuals say that the finger should not move at all but let the pulse of the finger do the vibrato. In pop music, the effect is sometimes heard on the guitar and some, but not all, singers use it (in some pop ballads, the vibrato can be so wide as to be a pronounced wobble). The use of vibrato in some folk music is rare, or at least less pronounced than in other forms of music, although in Eastern European gypsy music, for example, it can be very wide.
Wide vibrato, as wide as a whole-tone, is commonly used among electric guitar players and adds a vocal-like expressiveness to the sound.