Perspectives on uncertainty, tolerance, and precision in outdoor sound measurements

Abstract

Outdoor acoustical surveys typically involve greater variations in sound levels than indoor or laboratory measurements, whether the object is the determination of ambient statistical information, or the characterization of outdoor noise sources, such as for regulatory compliance purposes. Historical usage of each of the terms uncertainty, tolerance, and precision has been inconsistent and often vague, which leads to misunderstanding among all parties concerned with the definition of sound levels. The thing that has come to be referred to as uncertainty in outdoor sound measurements usually includes tolerance and precision. The field of acoustics is making progress in standardizing the definitions and uses of these, often misused, terms. This paper will discuss the perspectives of ISO, ANSI, ASME, and ASTM toward these terms, especially in light of recent standardization efforts. The use of the term tolerance, it will be recommended, should properly be a narrow one, as it is presently given in ASME performance test codes. This paper will summarize concise definitions and recommendations for standard usage, together with classification of the constituent elements of each term, in order to promote consistency within the acoustical community, thereby helping to insure improved clarity on the subject among all concerned parties.