on another note, If you played your pipes inside a helium-filled Zeppelin, would they go squeaky like a human voice does? 
Interesting! 
How about in micro-gravity? Astronauts tend to go sharp too as their vocal chords arenât being pulled down by graivty anymore either!
The problem comes from going from low altitude to high altitude. At high altitude maybe youâd scrape differently and seat the reed out farther and because of the dryness youâd adjust/make it for local conditions, but itâll work fine when youâre done. When you go from very low to very high, you probably will play higher pitched, then have to pull the reed out, and then end up with a little intonation problem or two. You could also just tape the heck out of everything and get it back in tune, but thereâs a change not in the reed, but the air column in the bore itself and the way it tunes/responds in âlighterâ air than heavier air.
In short, a bad analogy, but one that works for the moment, is like changing from a heavy guage string on a guitar to a very light one or vice-versa. More like not only going to lighter strings, but moving the bridge as well, shortening it a bit. Only with a wind instrument, itâs more like shortening or lengthening the bridle as go up and down, because the free-air resonance of the chanter changes slightly.
Iâd also like a physics consultation on the notion that air pressure remains constant as you gain altitude. The thing that causes air density is the weight of the air on itself, so the reason it would be less dense at higher altitudes would be the same reason it would be under less pressure, because there is less air stacked above it, compressing it. Thatâs what they taught me in boiler class when figuring the standing head of a pressure vessel.
Correct me if Iâm wrong, and Iâm sure yâall will.
Iâve done the thing up and down a lot on Highland pipes and smallpipes and my Zetland invention, but not uilleanns.
Royce
I actually did a âresearchâ project on this long ago in high school, my hypothesis being that heavier gases going through an instrument would produce a lower pitch than lighter gases. (I wondered why I was the one who was always flat, and whether I could attribute it to something other than an inferior embouchure.)
Unfortunately I no longer have the official results. But I bought a tank of helium and sure had a great time with my friends in the band. As I recall, the pitch did go up when we breathed the helium into our horns. 
Maybe thereâs a graduate student out there looking for a thesis topic who could be persuaded to pursue this one.
Jennie
Aha. Now this bit is crucial: when you flush your reeds down the toilet, they go the other way around in Australia than they would in Miami.
And they donât crow - they quack! 
djm
WeeelâŚI wouldnât call atop the Blue Mountains much of an elevation from sea level - not one that would make much difference to the pitch of pipes. Remember, what is termed a mountain here in Australia would generally be considered a mere hill in places like the US and Asia.
Cheers,
DavidG
Maybe a piper in Colorado can take a day trip to Mt. St Evans and give it the old college try? I wholeheartedly recommend that they get hammmered the night beforeâŚto aid in making it an experience of a lifetime.
This has been done at least twice (well, okay, without the Zeppelin); once at one of the US tionols (with a helium tank), and once in Belfast (with helium balloons). I believe a concert D set rose to about B above D, IIRC. Somewhere I have a recording of âboil the breakfast earlyâ played in this way⌠sorry, canât find it ATM. It sounded as wonderful and awful as you imagine 
- Bill
BTW I once played a sessiun at 40,000 feet. The reeds were unhappy, the tuning was âwoejusâ, but the pipes did play. I expect the humidity was approximately 0% as well.
I took a trip to Estes Park, CO back in June to attend a family get together, and brought the pipes. Not sure of the elevation there, but we were right outside the gate to Rocky Mountain Natâl Park.
Didnât notice any difference except I had trouble with my bottom D starting to âautocranâ. (fortunately I was able to resist the temptation to feck with the reed). I attributed this more to humidity change than air density. When I flew from there to Ireland for a 2 week vacation they played just fine.
-gary
Sorry, Gary, Ireland doesnât count. Everyone I know who has taken their pipes to Ireland reported on how well their reeds behaved there. Many people I know also report that reeds made in Ireland are crap when they get over here (myself included). Clearly the Irish are not reciprocating. A trade embargo may be necessary to beat them into line.
djm
Iâm going to Anniston, AL on the 27th and taking my pipes. Thatâs 4600 feet ASL to I assume about sea level. I assume that the altitude effect will be miniscule in comparison to the humidity difference. We have been running around 15% this week. Iâm sure AL is around 100% with Ivan in the nieghborhood. I have played my pipes at 8000 feet ASL, but they didnât seem to know the difference.
John
Yer probably right. Just keep in mind, âBoil the Breakfast Earlyâ will take twice as longâŚ
Bill
Itâs common knowledge amongst most wind players that you donât drink fizzy drinks before performing, because if you burp CO2 into your instrument, it will go flat until youâve blown all the air through it.
I can also confirm that helium is probably the next step in the GHB worldâs crusade to make the planetâs first ultrasonic bagpipe.
Cheers,
Calum
Well, back from Alabama and here is the report. My brass and plastic drone reeds didnât move at all, but my desert chanter reed was a different story. The humidity was generally 80 to 90% and my reed would play nicely for about an hour and then the back D would start breaking and the other notes went in every direction. Opening or closing the reed did not remedy this situation. My conclusion would be that desert reeds are not any happier going to the wet than humid reeds are coming to the desert. 
I am back home and the reed is back in its happy place now.
John
-As to whether various gases affect a wind instrumentâs pitch-my episodically derived answer is yes. I spent a few years as a TIG welder, often breathing some heavier-than-air argon flowing from the electrode torch. It lowered my upper-bass voice to Barry White (R.I.P.)
frequencies temporarily, more so in poorly ventilated areas.- Same phenomenon as breathing helium, but pitch went the other way. Pity I couldnât retain that resonance after leaving work!