Re: How does humidity affect pitch.

There are two things you need to think about for this project. 1) how does humidity affect the instrument's operation, and 2) how do you measure the pitch.

Humidity is the amount of water in the air. The more water there is in the air, the more dense the air is. This can affect woodwind instruments, but not a great degree. String instruments, on the other hand, are very strongly affected by the ambient humidity. One simple project that gets done often is the construction of a hygrometer (humidity meter) with a long piece of human hair. Hair, it turns out, changes its elasticity and length with the humidity. Accurately measuring the length of a piece of hair can give an indication of humidity. Most natural fiber strings, and even plastics to some degree, exhibit this same property. Since it is the length and density of the string that determines the pitch of a particluar note, violins (with cat-gut or other natural fiber strings) can be very sensitive to the humidity. Acoustic guitars are also quite sensitive to the humidity, provided that they have nylon strings. Brass, steel, or bronze strings are far less affected. Another cause of changes in tuning is the effect humidity has on wood. Guitars, violins, harpsichords, and other wooden instruments all are affected by changes in humidity. Pieces of wood actually warp, change shape, and elasticity with changes in the humidity. This also changes the pitch.

Pitch is really the measure of frequency of the sound waves that are generated by the musical instrument. There are many ways to measure the frequency of sound oscillations. First you have to detect the sound and convert it into electrical impulses. This is best done with a simple microphone. Then, the electrical wave can be measured with any one of several methods. The two easiest methods are using an oscilloscope or using a frequency counter. Your school may have either one available for you to use for your project. The oscilloscope graphs voltage as a function of time, and by measuring the time of one complete cycle, you can deduce the frequency of the wave, or in other words, the pitch of the note played on the instrument. The frequency counter automatically measures this period and calculates the frequency directly.

For further information, read about the physics of music.

I hope this helps,

-Fred