[Kryptid (OP)]

We are all familiar with the fact that inhaling helium makes your voice higher pitched. Does it do the same for all sounds travelling through it? If I was in a room filled with helium (while wearing an oxygen mask to avoid asphyxiation, of course), would things like footsteps, creaking doors, shattering glass, etc. sound higher pitched to me?

[paul cotter]

No it won't change sounds already made. What happens with inhalation is the resonant characteristics of the larynx are altered by a less dense gas. One can go the other way with a denser gas such as sulphur hexafluoride which will deepens one's voice.

[Kryptid (OP)]

No it won't change sounds already made. What happens with inhalation is the resonant characteristics of the larynx are altered by a less dense gas. One can go the other way with a denser gas such as sulphur hexafluoride which will deepens one's voice.

Would the same not be true of other objects set to vibrate in a helium atmosphere? Would shattering pieces of glass not have their resonant frequency changed?

[paul cotter]

I don't think so, Kryptid. The resonant frequency of the glass is determined by the physical properties and physical form of the glass. The larynx relies on gas properties, a bit like an organ pipe. Have look at organ pipes and how they work, with open and closed pipes influencing the frequency. There might be some slight effect with different gases.

[alancalverd]

SF₆ has the opposite effect, turning a normal voice into a sub-bass.

[Bored chemist]

Breathing helium does not alter the pitch of your voice.

It alters the timbre.
The pitch is dependent essentially on the tension and mass of the vocal cords (Men typically have bigger heavier voiceboxes and so they usually have lower pitched voices).

Helium affects the resonances of the cavities in the mouth throat nose etc and that's why  your voice sounds weird. You get a different set of harmonics.
If you learn to control those harmonics to tally with the fundamental of teh note you are singing, this happens.

Or this

So, helium won't affect the note of a tuning fork, but it will for a flute.

[alancalverd]

A debatable point! The human voice is certainly more akin to a flute than a tuning fork, but there's more to it.

Wind instruments select a principal resonant frequency from an "edge tone" - essentially a square wave that determines the lowest frequency that can be selected. The fundamental will be suppressed if it is off-resonance with the air column, so the resultant is dominated by the selected pitch which is recognised as the pitch of the note, with any remaining harmonics or subharmonics determining the timbre.

In the case of a flute, the resultant is almost a pure sine wave. Reed instruments have a lot of upper harmonics, and brass instruments are colored by subharmonics down to the fundamental.

The term "formant" rather than timbre is more commonly applied to voice sounds . The vocal cords are similar to the pursed lips of a brass player but the output spectrum is dominated by the higher resonances of the larynx for vowels and the mouth for consonants, and the formant, the dominant part of that spectrum, is a function of gas density.

[Bored chemist]

A debatable point!

The shape of the earth is "debatable", but the flat earthers are wrong.

The human voice is certainly more akin to a flute than a tuning fork

In the sense that, in order to sing low notes, one stretches one's neck to accommodate the longer wavelength.

Rather than holding a debate, we can look at an experiment.
https://newt.phys.unsw.edu.au/jw/speechmodel.html

[evan_au]

A tone played through a loudspeaker will have the same pitch in air or helium.

If it is a bass reflex loudspeaker, the higher speed of sound in helium will make the bass response tail off at a higher frequency than in air. So the frequency of the tone will be unchanged, but lower frequencies will be less loud.
https://en.wikipedia.org/wiki/Bass_reflex

[alancalverd]

https://newt.phys.unsw.edu.au/jw/speechmodel.html

which clearly shows that the formant peaks are not, even in this crude model, at the fundamental.

In speech, you may have the illusion that the pitch has changed because one doesn't think much about pitch when listening to speech.

You can also convolve the format spectrum with the sensitivity of the human ear, so whilst it is true that the absolute frequency range isn't affected by the air density, the perceived pitch is.

[alancalverd]

from: alancalverd on Today at 08:34:21
The human voice is certainly more akin to a flute than a tuning fork

In the sense that, in order to sing low notes, one stretches one's neck to accommodate the longer wavelength.

 I think you may be confusing a flute with a trombone. A  Conversational Russian coursebook that was in wide use in the Sixties included the vital everyday phrase "That is not a tractor but a trombone", which suggests a particular Russian idiosyncrasy.  Are you spying for Putin? You won't find much intelligence here!

[Bored chemist]

 I think you may be confusing a flute with a trombone.

In one case it's the length of an air column that determines the pitch, but in the other case, it's the length of the air column that determines the pitch.
Your job is to work out which is which.

[Bored chemist]

You won't find much intelligence here!

Depends  which posts I read.

[alancalverd]

In one case it's the length of an air column that determines the pitch, but in the other case, it's the length of the air column that determines the pitch.
Your job is to work out which is which.

Apart from the short tuning slide, the air column in my flute is exactly the same length at all times. I can however change the position of the principal resonant nodes by waggling the keys up and down. In principle, the air column length of a trombone is variable but right now, my slide has jammed, so I just have a very large bugle.

[Bored chemist]

can however change the position of the principal resonant nodes by waggling the keys up and down.

It's almost as if you are changing the length of the resonating air column.

[alancalverd]

We also play "It's Almost Like Being In Love" (Lerner and Loewe) but it doesn't sound like "Being in Love" (Wet Leg). Nor does a flute sound like a trombone - at least it shouldn't! 

The resonant column length changes in brass instruments, from a foot or so (piccolo trumpet) to 18 ft (Bb tuba) with roughly 12 equal fully resonant steps available to the valve combinations, but stays almost constant with woodwind - you just get a different distribution of nodes along the same tube length when you open and close the holes.  Just to make it more interesting, there's a difference between conical bore (horns and saxophones) and constant bore (trombones and flutes) sounds: conical bores favor even harmonics and switch whole octaves whilst constant bores favor odd harmonics and switch a twelfth if you alter the edge tone.

[Bored chemist]

When you play the flute, is the wood resonating, or is it the air?

[alancalverd]

Principally  the air, but the length of the air column and the timbre of the harmonics are determined  by the wood (or metal in most cases nowadays) .

But apropos the original question, Paul made an important point a while  back: if you filled your trombone or bagpipe with helium, would that alter its pitch? It's not a completely daft question because contrary to what the Health Security Agency (or whatever it is called today) thinks, you don't actually blow much gas out of a wind instrument. Indeed in the case of a flute, you don't even blow into it. So you could in principle fill the column with any gas you like.

[Bored chemist]

length of the air column and the timbre of the harmonics are determined  by the wood (or metal in most cases nowadays) .

So, a brass flute would sound more  like a tin whistle than like a wooden flute.
And a wooden flute would, I guess, sound like a recorder, rather a metal flute.

Or... not.

I suspect that the reason why plastic musical instruments exist is that, to a first approximation, the timbre depends on the shape of the instrument.

It would certainly be interesting to  fill a flute with helium (or hydrogen, if you are concerned that He isn't a renewable resource) and close it with cling-film so you don't blow any air through it.

I suspect the tone would not be improved by a bit of thin plastic, but it would illustrate a point.

: if you filled your trombone or bagpipe with helium, would that alter its pitch?

One way to find out; check on YT and see if it's been done.

Apparently, if you put helium into a bagpipe it turns into laughing gas.

[alancalverd]

Not really a proper controlled experiment.  Bagpipes always make people laugh. Or cry.

There is a significant difference in timbre between wood and metal flutes. A professional flautist friend selects from her considerable collection according to the mood of the piece she is recording or performing. I wouldn't dare to ask her opinion of a plastic flute, but

Fiberglass sousaphones can be found commonly in younger marching bands, such as middle schools, due to their lightened weight load. Depending on the model, the fiberglass version does not have as dark and rich a tone as the brass (King fiberglass sousaphones tended to have smooth fiberglass and a tone somewhat more like a brass sousaphone; Conn fiberglass sousaphones often had rough fiberglass exteriors and a thinner sound; the Conn is also lighter)

so the material and surface finish are important. Aficionados claim to be able to tell the difference between a brass and a silver band, but I don't aspire to play at such a level.