ABSTRACT
Sounds detected by the human ear only exist because of the medium of the air. A sound is a repeated pressure wave, a more or less regular change in the pressure of air arriving at the human ear, specifically at the eardrum. There is a further musical way of referring to pitch: classical church organs create sound using resonant pipes, the length of which were measured in feet. Electronic circuits can very easily be designed to create variations in output across the whole range of human hearing and beyond. A wave at three times the frequency of the fundamental can be referred to as the third harmonic, four times as the fourth harmonic and so on, and these frequencies are usually generated by musical instruments to some extent, though more quietly than the fundamental. Interestingly enough, all other waves can be created from a combination of sine waves of different frequencies or harmonics superimposed on one another.
