What causes multiphonics to sound unstable

[PiccoloTrombonist1]

I learned to play multiphonics/polyphonics last week, and with those comes some interesting facts. For example, the 5th, the octave, and the 10th all sound really stable, and sound like a chord with bad sound, but when I play a minor second, tritone, or some other dissonant pitch, it sounds really wobbly/unstable. I was wondering if anyone knows what exactly causes this sound to be made? It sounds almost like a 1-note trill.

[WilliamLang]

That's an acoustic beating - when you play notes that are nominally outside the partial series, the difference in tuning will cause the unstable sound, or beating, that you hear in the room. You can also hear this when you play slightly out of tune with someone else on purpose.

It's a fun effect! Especially as you get closer to the unison, you can somewhat control the rhythm in interesting ways.

[mbarbier]

I learned to play multiphonics/polyphonics last week, and with those comes some interesting facts. For example, the 5th, the octave, and the 10th all sound really stable, and sound like a chord with bad sound, but when I play a minor second, tritone, or some other dissonant pitch, it sounds really wobbly/unstable. I was wondering if anyone knows what exactly causes this sound to be made? It sounds almost like a 1-note trill.

One of my favorite subjects- done a lot of acoustic tests on this stuff. Slowly picking at an expansion of my book to cover it. Basically the horn has inharmonicity, like a piano and that causes issues.

Hopefully this all makes sense- I'm used to explaining it in just intonation ratios, so this feels a little inaccurate to my brain, but I think it should make sense?

The instrument itself has resonant nodes that can support or interfere with a lot of intervals. 4th/5ths/10th etc tend to be strong enough to override them whereas 3rd/6th/tritones tend to get pulled out of center by them.

Smaller intervals, like M/m2 tend to be close enough to the critical band that they've got a lot of interference regardless of the horn. They're excellent in an acoustic beating/rhythmic sense.

Basically with intervals like 3rds, if they don't have a resonance from the horn's overtone series to support them essentially won't center properly. A good way to test this is to play your middle Bb as a 3rd partial in first position. Sing a Bb above it that goes down to an A for a major 3rd. You'll notice the Bb slots extremely well and the A has a serious rub in it cause it's fighting against that Bb resonant node. Then do the same thing in 6th position where F is the 4th partial. You'll find that the Bb still slots quite well (though not quite as well) as it can override the resonant node. The A will slot extremely well because there's an A right there in the series.

You can do similar things for minor 3rd between the 5th and 6th partial and tritones between the 5th and 7th partial.

There's this piece of Wolfgang von Schweinitz's that pretty thoroughly explores using the horn's natural resonances to get strong enforcement/support for vocal multiphonics:

https://mattiebarbier.bandcamp.com/alb ... yodel-cry

Tldr: cause of the overtone series the horn has opinions of how multiphonics slot and if it's not 4th/5th the horn's opinions generally win.

I hope you're having fun- it's the best.

[PiccoloTrombonist1]

I learned to play multiphonics/polyphonics last week, and with those comes some interesting facts. For example, the 5th, the octave, and the 10th all sound really stable, and sound like a chord with bad sound, but when I play a minor second, tritone, or some other dissonant pitch, it sounds really wobbly/unstable. I was wondering if anyone knows what exactly causes this sound to be made? It sounds almost like a 1-note trill.

One of my favorite subjects- done a lot of acoustic tests on this stuff. Slowly picking at an expansion of my book to cover it. Basically the horn has inharmonicity, like a piano and that causes issues.

Hopefully this all makes sense- I'm used to explaining it in just intonation ratios, so this feels a little inaccurate to my brain, but I think it should make sense?

The instrument itself has resonant nodes that can support or interfere with a lot of intervals. 4th/5ths/10th etc tend to be strong enough to override them whereas 3rd/6th/tritones tend to get pulled out of center by them.

Smaller intervals, like M/m2 tend to be close enough to the critical band that they've got a lot of interference regardless of the horn. They're excellent in an acoustic beating/rhythmic sense.

Basically with intervals like 3rds, if they don't have a resonance from the horn's overtone series to support them essentially won't center properly. A good way to test this is to play your middle Bb as a 3rd partial in first position. Sing a Bb above it that goes down to an A for a major 3rd. You'll notice the Bb slots extremely well and the A has a serious rub in it cause it's fighting against that Bb resonant node. Then do the same thing in 6th position where F is the 4th partial. You'll find that the Bb still slots quite well (though not quite as well) as it can override the resonant node. The A will slot extremely well because there's an A right there in the series.

You can do similar things for minor 3rd between the 5th and 6th partial and tritones between the 5th and 7th partial.

There's this piece of Wolfgang von Schweinitz's that pretty thoroughly explores using the horn's natural resonances to get strong enforcement/support for vocal multiphonics:

https://mattiebarbier.bandcamp.com/alb ... yodel-cry

Tldr: cause of the overtone series the horn has opinions of how multiphonics slot and if it's not 4th/5th the horn's opinions generally win.

I hope you're having fun- it's the best.

That's Really Cool! Sometimes I'm able to reach an extremely high pitch (I describe it as purposely voice-cracking, It sounds like it's around the Bb5 area), and when I play multiphonics while singing that pitch, it seems like no matter how I alter the pitch, it slides in perfectly with the overtone series, and some notes even resonate with my horn opposed to the overtone series. Do you have any idea why this could be?

[WilliamLang]

Around the Bb5 region, the partial series on trombone kind of breaks down a bit - like you can hold a Bb5 and move the slide and keep the pitch consistent, for example. So if you're singing falsetto (which is what you might mean by voice cracking, if I had to guess) you'll be accessing that range where the horn will vibrate whatever pitch you put into it.

[mbarbier]

I'd agree with Will - there's just so many nodes up there and not really dominant ones so basically anything will resonant, if I'm understanding correctly.

[LeTromboniste]

Yes in that register, the partials are so close together and have so little definition that the instruments gradually shifts from being a resonator to being an amplifier (or a rather poor resonator for everything equally)

In the range where it is really a resonator, the multiphonics will logically work more efficiently if the horn can act as a resonator for both the played and sung notes than if it's acting as a resonator for the played note but merely an amplifier for the sung note – plus the pull from the nearby nodes where it actually wants to resonate like Mattie pointed out.

[Olofson]

If you play a Bb in first position, the second partial on the trombone, and sing an F a fifth above, if you are intune you will hear a D above. If you sing the Bb and play the F (third partial) you will still hear the D. If you sing the Bb and play the F on sixth position (fourth partial) you will still hear the D. I you play the Bb on trigger thre (Third partial) and sing the F, you will still hear the D. For the played tone the horn is allways acting as aresonator. The sung tone is resonating with the overtoneseries of the played tone, but more important, the intervall of a fith is like 2 to 3, if the interval is in tune the 2+3 = 5 witch is the third above. I t does also work the other way, 3-2=1. It also works if you buzz the Bb in your mouthpiece and sing the F. God luck. It works also in saxophone.

[LeTromboniste]

If you play a Bb in first position, the second partial on the trombone, and sing an F a fifth above, if you are intune you will hear a D above. If you sing the Bb and play the F (third partial) you will still hear the D. If you sing the Bb and play the F on sixth position (fourth partial) you will still hear the D. I you play the Bb on trigger thre (Third partial) and sing the F, you will still hear the D. For the played tone the horn is allways acting as aresonator. The sung tone is resonating with the overtoneseries of the played tone, but more important, the intervall of a fith is like 2 to 3, if the interval is in tune the 2+3 = 5 witch is the third above. I t does also work the other way, 3-2=1. It also works if you buzz the Bb in your mouthpiece and sing the F. God luck. It works also in saxophone.

Yes that is true, the resultant notes are always based on what notes you sing and play, regardless of the resonance nodes of the horn, but the point was that it's easier to sing the note and achieve the right balance and intonation to achieve the effect when the sung note is also at a resonance node of the instrument.

[timothy42b]

One of my handbell ringers found she could ring a bell, then whistle a note over the top for an effect that's probably similar. It worked for the "singing bell" (where you rub with a stick.)

[Olofson]

If you play a Bb in first position, the second partial on the trombone, and sing an F a fifth above, if you are intune you will hear a D above. If you sing the Bb and play the F (third partial) you will still hear the D. If you sing the Bb and play the F on sixth position (fourth partial) you will still hear the D. If you play the Bb on trigger thre (Third partial) and sing the F, you will still hear the D. For the played tone the horn is allways acting as aresonator. The sung tone is resonating with the overtoneseries of the played tone, but more important, the intervall of a fith is like 2 to 3, if the interval is in tune the 2+3 = 5 witch is the third above. I t does also work the other way, 3-2=1. It also works if you buzz the Bb in your mouthpiece and sing the F. God luck. It works also in saxophone.

If you play the Bb on trigger three (Third partial) and sing the F, you will still hear the D.

It is not harder to sing the F if you play Bb on trigger three.

Just singing the F in the horn on first, or even in sixth position is funny enough not that simple since the vocal chords is some distance from mouthpiece, the air column will be a bit longer. It is easier to sing the F slightly flatt.