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There is a less known technique for keyboard percussion that allows some form of pitch bending.

For example:

These are some way of getting it, but a similar effect is also possible by keeping the bottom of the mallet, and pushing it on a key by applying some horizontal friction in the direction of the key with different pressure, possibly near the string (I'll eventually add a video as soon as I can). While this normally gets the known pitch of the key, applying a varying pressure on it may also affect the tuning to some level.

It can be done on most metal keyboard percussion (vibraphone, glockenspiel, etc.), and some wooden keyboard percussion too, as long as their sustain allows it.

I've known about this since my initial studies, but I never had the opportunity to use it for performance, and therefore I never cared to learn more about it.

Still, I'm curious.

  • how does this happen?
  • what is the physics behind it?
  • what is the extent of the bending for a given "key"?
musicamante
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    I too would like to know the extent of the bending. I wouldn't understand the physics! The percussionists (Hirota/Yamash'ta) with the Red Buddha Theatre used to produce beautiful, down-bending, 4-note chords on the marimba. They would ripple-trem a long-held 4-note Cm chord and, at the peak of a crescendo, quickly move the mallet-heads towards the fronts of the keys, then slide them off and - sub>p - onto the Gm chord a 4th below, resuming the ripple-trem. The instrument seemed to sigh, and by leaning in towards the keys at each climax they gave the impression that the wood itself was bending. – Old Brixtonian Feb 28 '24 at 15:58
  • ... So at least a fourth in a downward direction. – Old Brixtonian Feb 28 '24 at 15:58
  • @OldBrixtonian That's quite interesting. Can you provide some reference for that? I honestly didn't know Red Buddha Theatre, I've found some sources on Youtube, but they're quite long and I didn't have time to search carefully enough. – musicamante Feb 28 '24 at 19:55
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    Sorry - what I described isn't on the record. That section ("Mandala") IS there, but without the bending. Also, I was wrong: it's in Dm. Sorry. So the 'slide' I described must have been from F major down to C major before returning to Dm. (It's at least 50 years ago!) – Old Brixtonian Feb 29 '24 at 20:13

1 Answers1

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For those who are really curious and not afraid of math, there is a full research article about the subject.

The short summary is that pitch bending by pressing a flexible mallet against the bar works so that the mallet head vibrates together with the bar, effectively adding mass to the bar. A bar that is heavier, but not more rigid, vibrates at lower frequency, somewhat similar to thicker string at same tension. The researchers tried attaching magnets to the bar, and it produces similar pitch change.

Because the strongest vibration mode in the bar is the one where center moves and the nodal points near ends where the bar is suspended stay in place, adding the mass to the center has stronger effect than adding it to near the nodes, and smooth movement of the mallet that touches the bar produces the smooth pitch bend. The amount of the bend is limited by how heavy mallet head can be held against the bar without chattering or absorbing too much energy.

The researchers claim that the practical limit is a semitone, but in the comments to the question there is a story of bending a full 4th, Cm to Gm, on marimba.

ojs
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    So at one position it should also be possible to change the pitch by pressing more or less hard (adding different weight) as long as it does keep the contact? Nice answer! – Tom Feb 28 '24 at 16:21
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    Does that mean the mallet in actuality is vibrating along with the bar, in effect becoming one vibrating object? – Michael Curtis Feb 28 '24 at 16:24
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    Yes, the mallet head is vibrating along with the bar. I'll update the answer to make it clearer. The trick requires that the mallet shaft is flexible enough to keep up with the vibration and maintain the pressure, and the mallet head is just the right hardness so that it doesn't bounce or absorb too much energy. As far as I can tell, the pressure should not have as much effect as the mass of the mallet head and the position, but I don't have an instrument I could try this with. – ojs Feb 28 '24 at 17:28
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    "the strongest vibration mode in the bar is the one where center moves and the ends stay in place" That is not correct. In the fundamental mode, the center of the bar moves AND the ends of the bar move. The bar is stationary at two nodes where the string holes are drilled. – Edward Feb 28 '24 at 18:01
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    @Edward technically correct, the best kind of correct. I edited it into the address, happy? – ojs Feb 28 '24 at 18:01
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    @ojs Thank you for that! I'm not so afraid of the math as I am about trying to dig into it, though ;-) Now that I think about it, what makes it work is that the added mass vibrates along with the bar, and it obviously makes sense: the added mass of a body that can still vibrate with the source without absorbing will decrease the frequency, which is why larger/heavier keys give lower pitch. This may also explain the comment by Old Brixtoninan (and negate that point on the paper, but I'll eventually read it more carefully): if a mallet with more weight is used, it may be possible to affect the » – musicamante Feb 29 '24 at 01:37
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    @ojs » pitch more than the mentioned limit of one semitone. I've some neodymium magnets around I use for fixing sheet music on stands while playing outside, I'll do some experiments and check the result by using both magnets and "mallet pitch". I'll eventually add a further answer about my findings, but right now I'm accepting yours as it clearly explains most of my questions. Thanks again! – musicamante Feb 29 '24 at 01:43
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    I can only speculate on this, but I think that because the wooden bars on marimba are lighter than metal ones on vibraphone, the mallet head is heavier in comparison and changes the frequency more. – ojs Feb 29 '24 at 08:49