Paper
This pilot study investigated extensively a small sample of day and night Ybackground noise in order to determine the significance of the choice of weighting filter, percentile value and measurement duration.Tape recorded day and night background noise was processed to determine Leg, Lmax, L1, L5, L10 . . . . . . ...L90, L91 . . . ..~L99 far ten octave'bands'and A' filter.The variation between day and night frequency spectrum suggests that the choice of filter characteristics is important.The shape of the cumulative distribution in the 1.90 1.99 region changes significantly between day and night indicating that the choice of LSD/LBS as background level may be critical.The confidence limits of background level values for different measurement time were determined.This paper suggests the type of investigation which should be undertaken by as many centres as possible in order to clarify the concept of a determinable background level.