Finger vibrato

Finger vibrato is vibrato produced on a string instrument by cyclic hand movements. Despite the name, normally the entire hand moves, and sometimes the entire upper arm.

In its pure form, vibrato is usually achieved by twisting the wrist rapidly to bend the note slightly, moving to and from the root note. However, the same techniques are applied at a slower speed to get pitch alterations.
In contemporary music, finger vibrato is also routinely used by classical guitarists on longer notes, to create an impression of a longer sustain. The technique is also used by jazz bassists to add depth of tone.

Radial pitch-shifting (string bending)

Radial pitch-shifting (also referred to as "string bending" or "bending") is produced by moving the stopped (held down) string with the left hand in a direction perpendicular to its axis and parallel to the fingerboard. This type of pitch-shifting is typically used in rock music.

Basic technique

To produce a bend the guitarist puts a finger on the string and then, while pressing the string down on the fret, strikes a tone, and pushes the string either up or down. This has the effect of stretching the string and thus makes its pitch higher. Generally a bend on the 1st-3rd strings will go "up" vertically as seen from the guitarist's point of view and a bend on the 4th-6th will go "down". The technique can also be used with distortion to make "screams".

Bending is usually limited to 1-2 semitones, rarely a bit more and involves overstressing the string which could lead to string breakage.

Difficultie

* The most difficult moment for beginners practicing bends is getting the note bent to proper pitch. Usually the bend changes note pitch exactly by 1 semitone or 1 whole tone (2 semitones), and most beginners fail to bend a string exactly to proper pitch, producing overbends and underbends. Most guitar teachers advise playing the target note on a higher fret, listening closely to its sound and trying to bend the string aiming to get exactly the same pitch.
* Especially in Blues playing, the target note can be slightly higher or lower than the fretted note one or two frets higher. It can be a quarter tone or not even exactly that, but a tone which is not present in the tempered scale, being a natural third or seventh instead (or close to it). These are the blue notes, one of which is e.g. between minor and major third. The exact location varies from performer to performer. This is microtonality and involves a lot of individual musical feeling, for the tone which conveys the intended emotion must be reached as exact as a tempered tone, otherwise it will sound just wrong.
* Bending (especially heavy bending, more than 1 semitone) usually involves touching more than 1 string with a left (fretting) hand, as seen in the illustration. Usually, making a heavy bend with just one finger is considered bad practice: one bent string will touch the adjacent one, the adjacent one will also produce some sort of unwanted tone that will result in an overall muddy sound. Thus, while bending one string, it is usually necessary to hold and bend (without striking) one or two adjacent strings in the direction of bend. The picture shows a guitarist bending a string with the ring finger while simultaneously holding and bending two upper strings with the middle finger.

Axial pitch-shifting

Axial vibrato is produced by moving stopped (held down) string with the left hand in a direction parallel to its axis, which increases or reduces the tension on the string and thereby alters the pitch. This type of vibrato is typically used by classical guitarists (see Classical guitar technique). It is also used to achieve a Backward, reverse or release bend, involving pressing the string on the fret, pulling it up (along its axis) to stretch the string first, and then striking the string. This causes the note to go flat, the reverse direction of straight bend.

Behind-the-nut pitch-shifting

Also known as "Behind-the-nut bending"

Press the string between the nut and the machine head (tuning key), and the pitch will shift.

* Classical guitar (nylon-string): This works on the unwound strings on a classical (nylon-string) guitar, and also works better on the strings whose heads (tuning keys) are further from the nut
* Bass guitar: works on all strings

The particular advantage of this technique is that unstopped notes can be pitch shifted (bent).

Variations

* Several strings can be bent at once.
* Innumerable bend patterns exist: for example, straight bending of a string 2 semitones up, then 1 semitone down, then 1 up, then 2 down.