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Summary

The acoustic science described above was intended to provide novices enough knowledge to understand the data and discussions put forth in the NPRM. Sound is a form of energy that is created when a medium vibrates, creating pressure variations (compressions and rarefactions of molecules) within a medium (such as air) which creates a pattern called a wave. Sound pressure over time creates peaks and valleys which make up the wavelength. The difference in acoustic pressure from the ambient pressure (no contraction of the medium) to the peak or valley of a wavelength is called the amplitude; the higher the amplitude, the louder the sound. The period of a wave is the time it takes for a cycle (a peak and a valley) to complete; a longer period indicates a lower pitch. The frequency of a sound is the number of complete wave cycles that pass by a given point in space every second; the higher the frequency, the higher the pitch.

The wavelength, amplitude, period and frequency are physical attributes of a sound wave that affect the human perception of loudness, pitch and timbre. These perceptions can be quantified using psychoacoustics. Psychoacoustics is the study of how humans perceive sound and forms the basis for extracting objective data from the physical characteristics of acoustic pressure (sound). Using the physical characteristics and psychoacoustic analysis, a sound is usually measured in decibels (dBs) within an octave. Octaves can be further broken down into one-third octave bands which provide more information about the spectral content of sound being analyzed. After reading this primer, the reader should understand what ''sound'' is, identify its different components, and understand how humans perceive sound and how each of these contributes to measuring sound.