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I have seen many videos where it looks like the guitarist is doing some vibrato and they make a rolling motion like in a violin, cello...

How can this work in a fretted instrument? As an amateur in both instruments, I don't know how can that work on a guitar.

I made a sketch of my understanding: example

As far I understand, the length of the string (blue), pressed over the fret (green), should be independent of the point where the finger (pink) is pressing inside the pressing area (yellow).

UPDATE: I find it hard to pick an answer as I think most of them are really good. So, if I understood correctly:

The change in pitch is done as follows: The increase in the position of a fixed point in the string (which means higher tension and therefore higher pitch) represented by the red d):

enter image description here

This would also mean that the vibrato goes in the opposite direction than the violin or other non fretted instrument right? Because usually you get the note in the right pitch and then start moving your arm away and therefore your fingertip (lowering the pitch) to then go back.

While according to this graph you would start in the position more "far away" and then close the gap. Right?

PD: The picture is exaggerated to show the two positions, usually you would reach both ends without lifting the finger.

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  • 13
    What's really entertaining is watching pianists do vibrato on a key! They swear it has an effect. "Hear it? Hear it?" "I dunno, dude... only with my eyes open." Jun 24 at 12:37
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    @AndyBonner - and in real life with 'aftertouch'!
    – Tim
    Jun 24 at 13:36
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    @DmitriUrbanowicz The other factor is: what you see and how you feel do matter. If the listener sees vibrato, they might perceive it. If the performer does something imperceptible that helps them feel more expressive, it impacts perceptible things like timing and articulation. Stagecraft isn't just pageantry. Jun 24 at 17:47
  • 2
    @AndyBonner: Re vibrato on piano: do not forget the clavichord, where the string runs over the hammer directly attached to the far end of the key you strike and hold depressed to sound and sustain the note. Greater pressure increases tension and ¿marginally? length, allowing one to alter the pitch while it sounds.
    – PJTraill
    Jun 24 at 18:48
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    @PJTraill the part of a clavichord that touches the string is called a "tangent," not a "hammer."
    – phoog
    Jun 25 at 5:44

10 Answers 10

7

On both fretted and non-fretted instruments, the vibrato works as a combination of change of resonating length, change of overall length, and change of tension. Many musicians simplify things when they describe how it works, and highlight only one or maybe two of these aspects. The reality is a bit more complex :)

The fret-to-string contact is a low mechanical impedance, so it reflects most of the incoming wave energy and establishes a null in the standing wave. The fret contact changes the length of the resonating part of the string. This is the key overlooked point: the overall length of the string and the length of the resonating part of it are independent.

Now, a string is a spring. If you press sideways on any linear spring constrained at the ends - be it a piece of wire, or a helical spring from a pen, you make the spring longer. Same happens to the string: it gets longer if you press on it. It happens whether you press it down towards the board, or laterally.

You can get fret action without changing the length nor tension of the string. Use a triangular rod, sized to fit exactly between the fingerboard/fretboard and the string, to provide the low mechanical impedance without deflecting the string, and thus without changing its length. You would press the string directly on top of that pseudo-fret to lower the mechanical impedance and improve the quality (q-factor) of the resonating part of the string.

But, obviously, on a fretted instrument, you not only bring the string down onto the fret - that already stretches it, but you then bring it further down towards the fretboard, making it even longer. This increases the length of the string, necessarily increasing its tension (unless the tuning pegs are loose).

You can see how the string stretches on the diagram below. Imagine that the string was painted in two sections, converging right above the fret when the string is free.

Diagram of string deflection

As the string is pressed down, the left (purple) part of it stretches past the fret (compare A, B and C). This is in spite of the length of the resonating string being largely the same in all three cases.

Now, when there's a nearby fret, the compliance of the string to lateral deflection (towards the fretboard and/or sideways) isn't constant like it would be in an unfretted instrument. The closer to the fret, the less compliant the spring is. And what does it mean? Suppose you deflect two identical springs the same amount: the more compliant one will experience less tension (tensile stress) than the more rigid (less compliant) one.

Thus, a string right behind the fret is a rather nonlinear spring, and the closer to the fret you press it down onto the fretboard, the more tension you introduce into the string. Note that the length of the resonating part of the string has not changed, but the overall length of the string then increases, and the tension in the string increases as well. The higher the tensile stress, the stiffer the string, and the higher the frequency of oscillation, and thus moving the finger towards the fret, while keeping the string down to the fretboards sharpens the note.

Of course the compliance of your finger also plays a role: the less compliant it is, the more it emphasizes the change in string's compliance towards the fret. Heavily callused fingers produce higher vibrato pitch range for the same range of finger motion.

And of course, we've only mentioned deflections toward the fret/fingerboard. You can also, additionally, deflect the string laterally, to further increase the string tension. And the vibrato can be a combination of rolling motion and sideways motion of the finger.

On the diagram below, 1 is the free string, 2 is the string lightly depressed straight down, and 3 is the string bent sideways.

Diagram of the sideways deflections

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  • In diagram B, it will be dependent on which side is longer, as to where the colour split goes. As shown, I'd guess the purple side is longer. But that won't always be the case with a fretted string.
    – Tim
    Jun 25 at 13:42
  • @Tim True! Then, as the string is pushed all the way down, the split will reverse and go over the fret and towards the inter-fret area :) Jun 25 at 18:48
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The length of the string is truly not changing, but there are other things that affect the frequency of the string vibrations. One is the density of the material (obviously this is not what vibrato changes), another is the cross-section of the string (ditto). The last one is the tension in the string. And that's what's being used here.

Essentially, you periodically pull at the string more and less, which periodically adds a bit of tension, and that results in the change of the pitch. (The tuning pegs on the guitar and other strings work in this way as well: by turning them, you add/reduce tension and that makes the pitch change.)

This is also definitely playing its part in vibrato on unfretted instruments; however I don't play any, so I don't really know which part of the vibrato on these instruments is due to what.

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    Same question as I left for @Tim: how is the tension changing if the length isn't?
    – Aaron
    Jun 24 at 7:59
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    @Aaron - it is, but it's microscopic.
    – Davor
    Jun 24 at 9:43
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    @Davor What I thought. Thanks. Now I can sleep! :-)
    – Aaron
    Jun 24 at 9:45
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    @Tim - you are applying lateral pressure to it, it's most definitely getting stretched so the entire string is actually longer. This is just basic material elasticity. Sure, it's not as stretchy as a rubber band, but on a microscopic level tension must stretch objects.
    – Davor
    Jun 24 at 11:07
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    It's worth distinguishing between the length of the string (which gets longer, because you're applying a force on it with your finger - also increasing the tension), and the vibrating part of the string (which remains the same length - from fretwire to saddle, as mentioned). Because the string is longer its tension is higher; because the part that is vibrating is the same length (but tenser), the note it sounds is higher in pitch.
    – psmears
    Jun 24 at 15:54
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The movements are similar, the effects are similar, but the causes are different.

Vibrato on a violin string is due to the length of the string changing. The player's finger rolls up and down the length of the string, which changes its pitch.

On classical guitar (electric and acoustic players also use it) the action of rolling the finger, within the confines of the fret it's in, causes the tension in that string to change. Roll the fingertip towards the guitar head, and the string's tension increases, roll towards the bridge, it decreases. Albeit slightly. There's also a slight change of tone. You're correct - the length of the string doesn't change - it's still from fretwire to saddle.

Compare that with the lateral movement used by electric guitar players, which stretches the string even more - a semitone or tone variance is quite common. Because the string is also being dragged across the fretwire, it increases the sustain, not really a phenomenon produced by the 'classical' vibrato.

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    the angle cannot change without the length changing. That would seem to be basic geometry.
    – Aaron
    Jun 24 at 8:19
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    @Aaron - it's the angle behind the fretwire that changes. I went to the geometry lesson!
    – Tim
    Jun 24 at 8:31
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    @fyrepenguin - saddle - fixed, fretwire - fixed. So, no, the sounding string length cannot change. The tension in the string is what changes, thus changing the string's pitch, and often, its timbre.
    – Tim
    Jun 24 at 8:47
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    @Tim I think I see. So when a string is stretched, even though the string itself is getting longer, its length relative to two fixed points remains the same, but with increased tension? Put another way: the string gets longer (or shorter), but the speaking length remains constant. Yes?
    – Aaron
    Jun 24 at 8:52
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    @Aaron - I guess so. The string itself is stretched, therefore it's (slightly) longer, but that's over its entire length, not the vibrating part. So, it's the increased tension that changes the pitch.
    – Tim
    Jun 24 at 10:44
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Already good answers, but I think I can add some info.

[I can think of at least two ways to do vibrato without the fingers: by subtly bending the neck and by using the erroneously named “tremolo” bar. But these are not relevant here.]

You can do two kinds of finger vibrato on guitar: moving the string up and down (like a bend); moving the string side to side. We’re talking about the second method here.

With this kind of vibrato, the string doesn’t change length, instead you are changing the tension in the string. As you “pull” the string to the left the tension increases and the note goes sharp, as you “push” the string to the right the tension decreases and the note goes flat. This is similar to how vibrato is done on bowed string instruments (e.g. violin), but it is not the same. On violin you roll the finger from side to side, which does make the string length change, and hence changes the pitch this way. With this style of vibrato on guitar, the finger remains perpendicular to the neck, and the whole hand moves side to side; the finger doesn’t roll. (Incidentally, I often refer to this kind of vibrato to pupils, as “violin-style” vibrato - maybe I shouldn’t!)

Lastly, it is worth mentioning why the “bend-style” and “sideways-style” vibrato are both used on guitar. Basically, they sound different and work better on different kinds of guitar.

Firstly, the sound: bend-style vibrato always makes a note slightly sharp. If you think about it, whether you bend a string upwards or downwards (towards floor or ceiling) the pitch always goes up. This makes this kind of vibrato less reliable tuning wise, and so maybe more suitable for electric guitar styles, e.g. Blues, Rock etc. Basically, it is less subtle. Whereas, side-to-side vibrato periodically goes above and below the main pitch. So on average, the note stays at the same pitch. This is more natural, more subtle, with more reliable tuning, and I would say more suited to classical music. It is more like the vibrato a singer would use.

And these usages match up well with the kinds of instruments broadly associated with these styles too. Bend-style vibrato doesn’t work very well on nylon strings; hence why side-to-side vibrato works better on classical guitar. Either work well on electric or steel-string acoustic, so the choice is more about sound and style. I would guess bend-style vibrato is more commonly used on electric and acoustic, but this is not a scientific observation!

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  • Still not with you! My finger doesn't slide anywhere, but the tip rolls left-right in the fret. I'll try to describe:put a fingertip on aa hard surface, hand relaxed. Keep the pressure on enough, as if fretting a string.Then move your whole arm side to side. The fingertip squidges in a sideways movement. That's what I think the question is about.
    – Tim
    Jun 24 at 12:18
  • It might be we’re describing the same thing in different ways! Ah well, that’s the beauty of SE, it seems you’ve described this better, so no doubt you’re answer will stay above mine. I might rethink my answer later if I have time, or just admit defeat!! Jun 24 at 12:20
  • Never give up! It's not an easy concept to describe - and you may well do it in a way that those who can't understand the other answers go 'Oh, it's that simple..!' Garn...
    – Tim
    Jun 24 at 12:23
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    As a violinist [aware that the discussion is about guitar technique, but still:], the day I learned vibrato my teacher told me "Pretend there's a wad of chewing gum on this table. You get your finger stuck in it, and then try to remove the gum by rubbing side to side." This gets the right points: There is lateral motion, but the actual flesh of the finger doesn't slide along the string. Jun 24 at 12:50
  • This is exactly what I’m getting at, Andy. Interesting that a violinist was taught that too… I’m glad that this post is exploring this technique through multiple answers. Jun 24 at 12:53
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Here's the part of string that does change the length — it's within the fret that's pressed. It's not the part that resonates, but by making the string stretched, more tension is on all of the string length.

Two versions of string being pressed between the fretbars. First presses the middle of string, the other presses near a fretbar. String makes different curve and that curve is of different length.

That being said, it's quite a subtle vibrato and to get anywhere near an expressive vibrato with a technique like this, one would have to apply the finger not between frets but behind the nut.

Btw the usual vibrato technique on the guitar also works by stretching the string. By bending it upwards, the resonant part even gets slightly longer, but the increased tension is what makes the pitch higher.

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    The more expressive vibrato is typically done by a left hand finger movement in parallel with the fret, as opposed to applying pressure behind the nut. You might run out of hands if you place one of them behind the nut. Jun 24 at 10:30
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    @JirkaHanika - the movement you describe, moving the string across the fretwire, is not the usual one for classical guitar playing. It's usually a roll between the fretwire you're on and the fretwire at the lower end of the fret. Fret at fret 5, and roll towards fret 4.
    – Tim
    Jun 24 at 10:50
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    @Tim, I’m not sure this is correct. I don’t roll my finger when doing vibrato on classical guitar. And as far as I can tell, if you do it doesn’t produce much noticeable vibrato. Jun 24 at 11:34
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    @Tim See my answer! Jun 24 at 12:03
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    @DKNguyen the thing is that classical guitarists actually pretend to do the vibrato between the fretbars: youtube.com/watch?v=oh-IUxWzfQk I agree, there's near 0 audible difference, that's why I take a stab at it and suggest trying to do it behind the fretbar :) But that's the technique this question is about.
    – Džuris
    Jun 25 at 10:26
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Two types of guitar strings:

  1. Nylon / other polymer / natural materials:
  • The tuning tension is low (compared to metal)
  • Bending the string doesnt achieve much of pitch change, because the string elasticity module is low as well. The tension simply doesn't change much.
  • The string is thick, making it easier to pull it by friction towards the head or the saddle, changing the tension of the sounding part of the string.

That's how vibrato is made. You pull the string longitudinally. You get vibrato towards both sharp and flat and it is not very deep (generally, less than half tone).

  1. Steel-based strings
  • The string is heavier, so the tuning tension is higher for the same length and tone
  • The elasticity module is high, small changes in lenght make audible changes in tension and pitch. The tone is sensitive to bending.
  • The strings are quite thin, so no significant longitudinal friction.

The possible vibrato approaches are bending (the tone always going sharp) or a dedicated vibrato machinery that is present on electric guitars.

One can even bend (non-destructively) or shake the whole (electric!) guitar and get more than a tone flat or sharp. Don't try this with an acoustic guitar, it will break.

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  • It's virtually impossible to pull a string longitudinally - especially the plain strings. A finger would merely slide along.
    – Tim
    Jun 25 at 13:37
  • @Tim how do you explain that the classical vibrato technique can bend the pitch slightly below the normal fretted pitch?
    – ojs
    Jun 25 at 17:00
  • @ojs - I don't, as it doesn't.
    – Tim
    Jun 25 at 17:12
  • @Tim how do you know? You're exactly in agreement with reality, but I'm interested in how did you end up being so sure.
    – ojs
    Jun 25 at 18:13
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    Digital tuners (those that are powered by a coin-size battery) are way too slow to catch vibrato. They measure the frequency averaged over 1/2 or 1 second. You need a full-blown spectral analyzer (or a trained ear) to catch this.
    – fraxinus
    Jun 26 at 6:18
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To answer the question of why this is done, the fretboard on a classical guitar is flat and it's easy for a nylon string to fly out from under your finger if you try to do bending vibrato like on an electric guitar.

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    Never found that to actually be the case. It's far more to do with the nylon strings and their tension (or lack of it) rather than flat fingerboards.
    – Tim
    Jun 25 at 7:46
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The other answers are great but I have to chip in because an obvious piece is missing in all of them.

You can see guitarists vibrato in all styles of music. Here's the kicker: a guitar vibrato isn't usually completely horizontal -. It's usually a bit diagonal / or circular o in motion. The difference is a vertical bend in the string.

Vertical bends of the strings will raise the pitch. I'm sure you've seen the stereotypical blues guitarists doing big bends with their eyes closed and a face of nearly constipated concentration.

P.S. You made me pick up a guitar and see how I do it. I mostly make a tiny oval.

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All of these answers seem correct. Sonny Edwards might be able to confirm, but for me, every classical guitar I've ever played the strings seem to roll or twist when you try to use vibrato, which feels horrible and makes me feel like I've lost some control. Maybe that also has something to do with it.

1

If you are pressing on the fret itself (not between frets) rolling in the direction of the fingerboard definitely works. It's identical to what you would do on a fretless guitar (or violin, or other instrument for that matter).

Rolling sideways works when you press in between frets because even though the fret is still pinching the string, the extra length from diagonal ealignment changes the tension.

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