4.1 Evaluation of Environmental Noise—Environmental noise is evaluated by comparing a measurement or prediction of the noise to one or more criteria. There are many different criteria and ways of measuring and specifying noise, depending on the purpose of the evaluation. Some evaluations are limited to determining compliance with existing regulations or ordinances. Others are done in the absence of such requirements or to supplement regulatory evaluations where the regulations do not address fully or at all the issues of concern.

4.2 Selection of Criteria—This guide provides information useful in selecting the appropriate criteria and measurement method to evaluate noise. In making the selection, the user should consider the following: regulatory or legal requirements for the use of a specific criterion; purpose of the evaluation (regulatory compliance, compatibility, activity interference, aesthetics, comfort, annoyance, health effects, hearing damage, etc.); types of data that are available or could be available (A-weighted, octave band, average level, maximum level, day-night level, calibrated recordings including .wav files from which various measurements could be made, etc.); and available budget for instrumentation and manpower to obtain that data. After selecting a measurement method, the user should consult appropriate references for more detailed guidance (1).7

4.3 Objective versus Subjective Evaluations—This guide discusses objective sound criteria based on measurements and regulations based on such. Some local noise ordinances are based solely or partially on subjective judgements of noise. Enforcement of these can be easily challenged and, in some jurisdictions, they are not permitted. These are not further considered in this guide. One way to address such situations is to evaluate the sound based on reasonable objective criteria.

4.4 Soundscape Methodology—The overall sound environment as perceived outdoors is often called a soundscape. Soundscapes have both objective (quantitative) and subjective (qualitative) attributes. A soundscape evaluation methodology is evolving which includes methods and criteria that rely extensively on qualitative factors, both acoustical and non-acoustical, while including requirements for quantitative sound measurement. Two basic tenets of quantitative soundscape measurements are that the ambient sound at a location is comprised of a combination of specific acoustic events that can be measured individually and in combinations; and that the sounds should be measured using methods that represent the ways in which they are perceived by people. Development of such measurement methods specifically for soundscape studies is a part of ongoing research and is not specifically discussed in this document.

1.1 This guide covers many measurement methods and criteria for evaluating environmental noise, some of which are required to be used for specific purposes by governmental regulations. It is intended to provide users who may not be familiar with them with an overview of the wide variety of available methods and criteria. It includes the following:

1.1.1 The use of weightings, penalties, and adjustment or normalization factors;

1.1.2 Types of noise measurements and criteria, indicating their limitations and best uses;

1.1.3 Sources of criteria;

1.1.4 Recommended procedures for criteria selection;

1.1.5 A catalog of sources of selected available criteria; and

1.1.6 Suggested applications of sound level measurements and criteria.

1.2 Criteria Selection—Thorough evaluation of noise issues requires consideration of many characteristics of both the sound and the environment into which it is introduced. This guide will assist users in selecting criteria for the following:

1.2.1 Evaluating the effect of existing or potential outdoor sounds on a community considering the magnitude and other characteristics of the sound and environment;

1.2.2 Establishing or revising local noise ordinances, codes, or bylaws, including performance standards in zoning regulations; and

1.2.3 Identifying and evaluating compliance with regulatory requirements that do not specify an acoustical measurement method or criterion or which are unclear.

1.3 Reasons for Criteria—This guide discusses the many reasons for noise criteria, ways sound can be measured and specified, and advantages and disadvantages of the most widely used types of criteria. The guide refers the user to appropriate documents for more detailed information and guidance. Users needing further general background on sound and sound measurement are directed to the books listed in the References section.

1.4 Criteria in Regulations—Certain criteria are specified to be used by government regulation, law, or ordinance for specific purposes. Any investigation or evaluation of a community noise issue must start with identifying applicable regulations and evaluating compliance with them. This document discusses but is not limited to regulations and ordinances. Due to the wide variation in local regulations, those are discussed more generally, and specific criteria are provided only from national government regulations. Regulations typically specify measurement methods and criteria for purposes of the regulation. Local ordinances must be written for ease of enforcement and cannot address all situations satisfactorily without becoming too complex. Such ordinances are also often prepared without competent guidance and can be too restrictive in some cases and not restrictive enough in others. Other regulations that determine government spending for noise control must balance that cost to the general public against impacts on individuals.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.