Appendix 4 - Noise impact assessment

   APPENDIX A – GLOSSARY OF ACOUSTIC TERMS
   The following is a brief description of the technical terms used to describe traffic noise to assist in understanding the
   technical issues presented in this document.


   Event maximum sound pressure level (LA%,adj,T), Lmax L01
   The “Lmax” level is the loudest sample within a measurement period; while the “L01” level is calculated as the noise level
   equalled and exceeded for 1% of the measurement time, for example 9 seconds in any 15 minute interval. The Lmax and
   L01 descriptors are appropriate to characterise single events, such as from impulsive or distinctive pass-by noise. However
   the L01 descriptor provides a better picture of recurring discrete noise events as it removes anomalies from the data (e.g.
   bird calls close to the microphone). Both of these level can be adjusted for tonality or impulsiveness.


   Average maximum sound pressure level (LA%,adj, T), L10
   The “L10” level is an indicator of “steady-state” noise or intrusive noise conditions from traffic, music and other relatively
   non-impulsive noise sources. The L10 level is calculated as the noise level equalled and exceeded for 10% the
   measurement time, for example 90 seconds in any 15 minute interval. The measured L10 time-intervals for
   day/evening/night are arithmetically averaged to present the “average maximum” levels of the environment for
   day/evening/night. The level can be adjusted for tonality or impulsiveness.


   Background sound pressure level (LA90,T), L90
   Commonly called the "L90" or "background" level and is an indicator of the quietest times of day, evening or night. The
   L90 level is calculated as the noise level equalled and exceeded for 90% the measurement time. The measured L90 time-
   intervals are arithmetically averaged to present the “average background” levels of the environment for day/evening/night.
   The level is recorded in the absence of any noise under investigation. The level is not adjusted for tonality or
   impulsiveness.


   Equivalent Continuous or time average sound pressure level (LAeq,T), Leq
   Commonly called the "Leq" level it is the logarithmic average noise level from all sources far and near. The maximum 1-
   hour levels within the day/evening/night time intervals are referenced for building design. The level can be adjusted for
   tonality.


   Rated Background Level, RBL
   The Rated Background Level is the overall single-figure background level representing each assessment period
   (day/evening/night) over the whole monitoring period.


   Free-field level
   A sound level that is measured at a distance of more than 3.5 metres from a wall or facade.




© Alpha Acoustics Pty Ltd                                                                         Page 21 of 25
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