ABSTRACT
Sound is the oscillation of molecules in a medium. The energy of the oscillations is transmitted as a longitudinal wave in which the medium is alternately compressed and rarefied. This can be measured as periodic oscillations in the pressure of the medium. Differences in sound pressure level (SPL) are perceived as differences in the loudness of a sound. Loudness is the perceived magnitude of a sound but it varies with frequency for tones that have the same SPL. It is defined as the SPL of a tone with a frequency of 1000 Hz which matches the loudness of a sound. However, virtually no naturally occurring sounds or musical notes are pure tones, but have harmonics that span many octaves and permit them to be resolved even when simultaneous. The frequency response of the human ear is from 20 Hz to 20 kHz optimally, but rapidly narrows with age, with most of the loss occurring at the higher frequencies.
