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Discussion Starter · #1 ·
Hey guys, question here about tuning. At high altitude, air slows down which means each frequency gets a shorter wavelength. Since the toneholes on any woodwind select wavelength not frequency, the pitch should drop at high altitude. That's because when sound moves slower, the same wavelength corresponds to a lower frequency.

String instruments, though, should be totally unaffected by altitude. Frequency of a string depends on the string's mass, tension and length. So a violin should have the same pitch from sea level to Mt. Everest.

According to references I've checked, the speed of sound at 6000' altitude is about 2.1% slower than at sea level. That means a given wavelength corresponds to a pitch 2.1% lower. This means a woodwind set for A=440 will play A=430.8 at 6000' feet.

That is a HUGE difference in pitch. How is it possible for an orchestra to tune at high altitude when all the woodwinds have dropped in pitch while strings are unaffected?

Is there an error in my calculation - or in my reasoning?
 

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It's a conceptual problem here.

The speed that sound propagates changes because the density of air changes at different altitudes. This has no effect on wavelength or frequency, just it's rate of travel.
 

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Discussion Starter · #3 · (Edited)
Basic physics says for any wave:

speed = frequency * wavelength

So if speed drops, the same frequency must have a shorter wavelength. Or conversely, the same wavelength corresponds to a lower frequency.

What am I missing here?

P.S. to understand intuitively why speed *must* affect frequency and wavelength, imagine the following. You are hearing a 440 Hz tone. Imagine this as a sine wave traveling so 440 peaks hit your eardrum per second. Now slow down this wave without changing its shape. Obviously, because it's moving slower, less than 440 peaks will hit your eardrum each second. If you want 440 peaks to hit your eardrum per second at this slower speed, the peaks must be closer together. But that means their wavelength must be shorter.
 

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MRC01 is right about the physics. But I would assume any non-electronic instrument would vary the same way. Strings, brass, woodwinds, tuned percussion are designed to produce sound with a wavelength set by their physical dimensions...and string tension.

I would assume the strings ought to be tuned lower and along with any synthesizers being used.

Yes your are right, 2.1% is around 30 cents, a fairly big amount.
 

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My faulty reasoning. My memory for physics isn't as good as it used to be.

There is, indeed a problem with tuning at greater altitudes, and your physics are correct. There are actually a couple of studies by Gary Moody, the oboe prof at Colorado State about the challenges and solutions of making double reeds for high altitude playing. (I didn't check the articles, I'm not sure if it's about tuning or the operation of reeds at high altitude.)
 

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Discussion Starter · #6 ·
Guys, I just figured it out. I always thought that sound traveled slower at altitude primarily because the air was less dense. This seems intuitive because the density of a material does affect the speed of sound - sound does indeed travel faster through water, wood, etc. compared to air.

But it turns out this intuition is wrong. The speed of sound correction for altitude is based primarily on temperature, a little bit on humidity, and has almost nothing to do with air density.

What that means is that at high altitude, if you're indoors in a temperature controlled room, the temperature is probably about the same as what it would be at sea level, so the speed of sound is about the same - in that room - as it would be at sea level. So pitch is relatively unaffected.

It just goes to show - truth is stranger than fiction, and intuition often leads us astray.
 

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Discussion Starter · #7 ·
MM said:
MRC01 is right about the physics. But I would assume any non-electronic instrument would vary the same way. Strings, brass, woodwinds, tuned percussion are designed to produce sound with a wavelength set by their physical dimensions...and string tension.
Strings should not be affected because the frequency emitted by a vibrating string does not depend on the speed of sound. A string's fundamental frequency is based solely on its mass, length and tension.

A woodwind, on the other hand, produces whatever frequency whose wavelength is equal to the distance to the tonehole. So a woodwind's frequency depends on the speed of sound.
 

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Seems my experience was correct, but my reasoning is still faulty.
I hate that. (I'll get over it).:cry: :cool: ;) :)
 

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Discussion Starter · #9 ·
Me too - my brain still hurts from the concept that air density doesn't affect the speed of sound. But learning new things is cool no matter how much it hurts :)
 

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MRC, isn't the string's sound wavelength set by its length, not its frequency?

If the answer is yes then frequency is still depend on altitude, for the same tension.
 

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Discussion Starter · #11 ·
As I understand the physics, a string vibrates at a frequency that depends on the string's mass, length and tension.

This is a key difference between string instruments and wind instruments. The inherent design of a string instrument produces a frequency of sound. The inherent design of a wind instrument determines a wavelength of sound. Surrounding atmospheric conditions determine what frequency corresponds to that wavelength. So wind instruments depend on atmospheric conditions in a way that string instruments don't. The pitch of a string instrument should be totally unaffected by the speed of sound. But the pitch of wind instruments is strongly affected by the speed of sound.

But that is not to say that string instruments are unaffected by their environment. I believe temperature is the key factor affecting both, but in opposite directions.

For woodwinds, decreasing temperature means decreasing speed of sound, which means a lower frequency corresponds to the same wavelength, so the pitch drops with temperature. This any wind player knows from experience.

For strings, decreasing temperature contracts and stiffens the string, which increases pitch. So pitch rises as temperature drops. I am not a string player so this is just a guess on my part.

In short, winds go sharp as they warm up while strings (should, I believe) go flat.
 

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This is my understanding also. I've also experienced it firsthand:shock: :shock:
 

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Excellent question MRCO1! It really got me thinking. I think the key issue is temperature: strings go sharp, winds go flat with lower temperature.

One addition I might make is that regardless of the method of sound production, all instruments ultimately produce vibrations in the air (frequencies). Once the vibration is created any speed of sound issues will affect all instruments equally as the sound travels to the ear.

Strings vibrate based on length, tension (which is temperature sensitive), and mass. Usually changes in altitude are accompanied by changes in temperature, so hopefully the string section will adjust.

I believe that the vibrations that woodwinds produce are soley dependent on the air inside the instrument. I know I have to warm-up more when I play clarinet at altitude, but once the temperature and humidity is sufficient inside, the horn is in tune.
 

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The drawing of the bow across the string also pulls the string slightly out of tune. This is more of a problem on new strings. For the first day they can't be played in tune as they are constantly stretching. This is why you see tubes filled with used strings in string players cases, for emergency string replacement. Most of the stretching has taken place - but some will still occur. I often prefer to go without the string if it breaks during performance. It's not like switching to another reed, which I am known to do on occasion as needed during a gig.
 

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Hmmm...interesting.

I just happen to have access to an altitude simulation chamber which can vary the air pressure from sea level to about 10,000 feet of simulated altitude (I know, some guys have everything).

I might just take my sax in there sometime and see how much the tuning changes.
 

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Yeah, I just did a little experiment with a rubber band...I think you are right. My incorrect intuition was that the sting would vibrate at multiple half-wavelengths of its length, with some second-order correction due to mass and tension and the fundamental (non-harmonic mode) would correspond to one half-wavelength. This is very obviously WRONG--otherwise all of the strings of a violin or guitar would have about the same pitch. Sometimes differential equations work better than intuition.

On further thought, my error is due a mixup between the velocity of propagation of sound with the velocity of propagation of mechanical waves in a string. The latter must be a strong function of string tension. The fundamental is still a half wavelength, just like for a flute, but one uses a very differential velocity of propagation to calculate frequency from a given wavelength. The frequency of the string's vibration is the same as the frequency of the sound you hear, but the wavelength of the sound is different from that of the mechanical vibrations.
 

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gelliot2 said:
Hmmm...interesting.

I just happen to have access to an altitude simulation chamber which can vary the air pressure from sea level to about 10,000 feet of simulated altitude (I know, some guys have everything).

I might just take my sax in there sometime and see how much the tuning changes.
I was thinking about playing my horn at the beach (sea level), Then driving to the top of Mauna Kea (13,500 ft). Then I remembered how dizzy I got the last time I did it...
 

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gelliot2 said:
Actually the chamber is for testing cars, so you can bring the car along too.

What is it exactly - a pink T-Bird?
At least your doing better than Carl H.--he thought it was beige.
It's a pink '61 caddy. I belongs to the drummer in the classic rock band I play in. We did promo shots with the caddy. I thought the pic made me look thin. ;)

Sometimes we ride to gigs in it.
 

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hakukani said:
At least your doing better than Carl H.--he thought it was beige.
It's a pink '61 caddy. I belongs to the drummer in the classic rock band I play in. We did promo shots with the caddy. I thought the pic made me look thin. ;)

Sometimes we ride to gigs in it.
My sister had a 76 ford the color I see in my monitor, it was called "buckskin" by Ford. I used to prefer the big old cars, when I could afford fuel for them. A buddy of mine used to drive a black '73 98 with a rocket 455. He switched to a 76 town car after somebody sugared his fuel tank. I think those were the last BIG cars I used to regularly ride in. After my brother totalled my 73 ltd 2 dr with a big block, I never went back to a real full size. My volvo wagon would darned near fit in the trunk of that caddy in your pic.
 
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