The use of vibrato is intended to add warmth to a note. In the case of many string instruments, the sound is strongly directional, particularly at high frequencies. 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. It may also help a solo player sound 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.
You can think about Vibrato as an effect added to the note itself. However, in some cases, it is 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 Leonard Bernstein when producing his record album “What is Jazz” to demonstrate the difference between the two. Despite his technique, he was unable to play without it. The featured saxophonist in Benny Goodman’s Orchestra, George Auld, 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.
When used by vocalist or instrumentalists, it can add a sense of warmth and life to a musical line. The width and frequency of the vibrato and their evolution over time are important expressive decisions for many performers. It can also help an instrument or voice to stand out from an ensemble. A single musical note will contain energy at discrete, harmonically related frequencies. But by varying the pitch back and forth, a single note can use more of the frequency spectrum. Additionally, producers sometimes us it to cover slight errors in pitch. This is because it is easier to perceive a steady pitched sound as out of tune than one containing it. However, the use of vibrato in order to cover the pitch errors is generally considered as a poor musical practice.
Vibrato audio effect is not as flexible as the performer’s natural vibrato. This is because the LFO operates at the constant rate and width regardless of the musical material. Also, a simple implementation does not synchronize with the beginnings and the endings of individual notes as a performer would. More advanced implementations do and they are available in some synthesizers.
Use with Reverb
Thought it is possible to imagine a vibrato effect with a pedal or another control to give the user more control over the LFO, this is rarely the case in practice. Nonetheless, even a fixed-frequency vibrato can add warmth and body to the sound of the instrument. This is especially the case when you use it with reverberation.
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