Pitch and Frequency

A sound wave is introduced into a medium by a vibrating object. Regardless of what the vibrating object is, it is moving back and forth at a given frequency, or pitch. Frequency is measured in Hertz, or number of cycles per second.

Hertz (Hz) = The number of cycles per second or number of times the object moved back and forth in one second.

If you hit the note of middle C on the piano, you will hear a sound vibrating at about 264 cycles per second, or 264 Hz. All of the particles in the medium will then be vibrating at a frequency of 264 Hz. If you looked at the transverse pressure waveform crated by a microphone, you would see it oscillating at the same 264 Hz.

The frequency, measured in Hertz of a sound, is also known as the pitch by musicians. A higher frequency corresponds with a higher, sharper pitch and a lower frequency corresponds with a flat or lower pitch.

Some musically trained people are able to detect frequencies as little as 2 Hz. In the field of sound therapy, we have found that changes of as little as 0.001 Hz or less can have a difference.

Period

If you look carefully at the pressure plot created by the microphone, you will notice that each individual cycle is displayed in time. Another way you could look at frequency is to look at the time between each cycle. The time between adjacent cycles is known as the period. Mathematically, the frequency and period are related as shown in the following equations:

Period = 1 / Frequency

Frequency = 1 / Period

In the example above, the frequency of 264 Hz of middle C, or time time between adjacent cycles, is 3.79 milliseconds, or 0.00379 seconds.

Musicians know that making two or more sounds together can have particularly pleasing sensations.