Helium and Pitch

Do you know why brass and woodwinds go sharp as the instruments get warmed up? It’s common for people to respond that it’s because as the temperature goes up objects expand (true), but if you think this through carefully you’ll realize that this would cause the opposite. The actual effect of the expansion of the instrument due to the temperature increase is pretty negligible, there’s another more dramatic effect that pulls the pitch in the opposite direction. Sound travels faster in a warmer temperature making the pitch go higher.

Many years ago I took a Brass Pedagogy class over to the Physics Department and we did some informal experiments filling up our instruments with helium and trying to play this way. Because sound travels dramatically faster in helium the pitch was quite a bit higher pitched. The woodwind and vocal students in my class had a lot of trouble playing a brass instrument this way, the brass majors found it a little easier. Trying it out myself I found it odd to feel the pitch I was playing but hearing a higher pitch but was able to ignore it and play a steady pitch. This suggested to me that the more experienced the brass player the more “muscle memory” they use to help them play with accuracy.

Here’s a video that demonstrates the same experiment filling up instruments and lungs with helium and showing the humorous results.

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