Analog Sound--Frequency and Amplitude A sound can simply be defined as a vibration that is capable of being detected by a human ear. When our eardrums vibrate, we are "hearing a sound." The rate at which our eardrums (and the sound-producing object) vibrate is called the vibration's frequency. Frequency is measured in units called Hertz (or Hz), named after the German scientist Heinrich R. Hertz. A Hertz is defined as the number of vibrational cycles that a sound produces in one second. A single Hertz is equal to one cycle per second, which is far too low a frequency for the human ear to detect. The Hertz unit is usually combined with metric system prefixes to produce various subdivisions. These are commonly known as the kilohertz (kHz), the megahertz (MHz), and the gigahertz (GHz). A finely tuned human ear is capable of detecting a broad frequency range, from 20Hz to 22.05kHz (22,050Hz). The range narrows as we grow older, and as our hearing is dulled thanks to the effects of listening to loud noises over long periods of time. It's important to treat your hearing like gold! So how does the frequency spectrum translate into musical terms? Consider a stringed instrument, such as a cello, which has a pretty wide frequency range, as an example. When a note is bowed on the lowest string, the string vibrations are very slow, as the diameter of the string is quite thick in comparison to the highest string. This produces a very low frequency vibration, which in turn means that the sounded note is very low in pitch. On the other end of that spectrum, if your cello player were to then play a note on the highest string, the vibrations would be much more rapid, creating a tone with higher frequency and pitch. Frequency also has a counterpart element, called amplitude, which is simply the volume of the