Vibrato on the guitar can make a note really come alive. Vibrato can make the note sustain for a longer time, give it more character and achieve a ‘singing’ quality that works wonderfully in melodic passages.
Vibrato on the guitar is different to vibrato on violin, viola, cello or double bass. These bowed string instruments do not have frets like the guitar does, so when they do vibrato they are actually changing the length of the string slightly by rocking the finger back and forth. The same rocking motion does not achieve anything on the guitar because the fret determines the pitch regardless of where you place, or wiggle, your finger in between the frets.
To create vibrato on the guitar you actually have to pull and push the string so that you are in effect doing what the tuning pegs do; you are tightening and slackening the strings. When you pull the string towards the tuning pegs you are tightening the tension and the pitch will go up, when you push the string down towards the bridge you are lowering the pitch. When doing vibrato, you need to combine the pulling and push motion so that the pitch gets distorted slightly above and below the normal pitch.
On electric guitar you will often see players doing a vibrato that bends the string vertically towards the other strings. This bending also tightens the string in the same way that pulling the string horizontally does, this raises the pitch but will never make the pitch go below the original note. This technique is more common on the electric guitar because the strings have a higher tension, you can use this technique on the classical (nylon string) guitar but it has a different effect. Sometimes it can be very useful for a special moment where you want to use this bending type of vibrato, but in general classical guitar technique uses the more subtle variety as described above.
