The lowest frequency produced by any particular instrument is known as the fundamental frequency. The lowest frequency produced by any particular instrument is known as the fundamental frequency. The fundamental frequency is also called the first harmonic of the instrument.

A harmonic frequency is a multiple of a fundamental frequency. A fundamental frequency of 500Hz has a first harmonic frequency of 1000Hz, double the fundamental frequency. Its second harmonic is 1500Hz, the third harmonic is 2000Hz and so on. A musical instrument produces both fundamental and harmonic frequencies, which allows the human ear to discern the differences between instruments even if they are playing the same note.

An overtone is any frequency higher than the fundamental frequency of a soundOpen-End Air ColumnsMany musical instruments consist of an air column enclosed inside of a hollow metal tube. Though the metal tube may be more than a meter in length, it is often curved upon itself one or more times in order to conserve space. If the end of the tube is uncovered such that the air at the end of the tube can freely vibrate when the sound wave reaches it, then the end is referred to as an open end. If both ends of the tube are uncovered or open, the musical instrument is said to contain an open-end air column. A variety of instruments operate on the basis of open-end air columns; examples include the flute and the recorder. Even some organ pipes serve as open-end air columns.A closed air column is a column of air that is open at one end only. It can be made to resonate with a source of sound by allowing sound waves to travel down its length, reflect off the closed end, and create a standing wave interference pattern within the air column. In order for the air column to begin resonating, it must be one of several possible "proper" lengths related to the wavelength of the source. When the air column resonates, it will emit a sound of noticeably increased volume.