the trrl noise logging equipment is a ten microphone system designed to accumulate information automatically about the temporal distribution of noise over a selected area. it is capable of operating continuously for 24 hours or more. this paper describes the components of the logger and discusses its performance in the field. the accuracy of the system depends upon the rate of data acquisition. at the rate currently in use, the standard error associated with estimates of the l10 and l90 indices is typically + 1.0 dba at sites alongside busy roads. this compares favourably with the precision offered by the more widely used tape recording method. the results of an experiment carried out in birmingham are reported. using the trrl equipment it was found that 360 microphone-hours of data could be comfortably collected and analysed in two weeks, involving a total staff effort of approximately 180 man-hours. at sites closer to the laboratory the staff requirement can be approximately halved. a computerised noise mapping technique has been adapted to display the birmingham data. in its present form, however, a considerable amount of data pre-processing is required and for this reason the method is not recommended. finally, modifications to the system are proposed. a mini-computer will be used to control high speed scanning of the microphone outputs, and will also analyse the data on-site. (a)

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