ABSTRACT
The spectral character of noise can be divided into three basic and distinctly different types discrete frequency noise, broadband noise, and impulsive noise. Furthermore, most noise sources will take on one or more of these sub-characteristics and as such will possess a unique acoustical signature. This chapter discusses the analytical representation of the basic spectral characteristics of sound and essential noise-producing mechanisms. Examples common in industry will be used to illustrate these powerful diagnostic methods. In addition, for a variety of reasons such as human response and regulatory criteria, the spectral character of noise is often altered by application of weighting scales. Impulsive or impact noise is best characterized as a transient acoustical event of short duration, usually less than 0.5 s. In summary, impulsive or impact noise can be described in terms of a well-defined spectral character. The acoustical engineer often must alter or weight the spectral character of noise for comparison to subjective, psychoacoustic, or regulatory criteria.
