DeltaOHM HD2010UC/A, Руководство по эксплуатации, Страница: 131 / 162

HD2010UC/A
- 131 -
V4.1
S
TATISTICAL
A
NALYSIS
If you need to examine, from a statistical viewpoint, the distribution in time of the sound pres-
sure level, you have to use the percentile levels. A percentile level, symbolized as L
x
is defined as
the sound level being exceeded by the X percentage during the total time. To calculate the percen-
tile levels you first need to classify the sampled sound level according to regular intervals (usually
1/8s) in width classes, usually between 0.1dB and 2dB. At the end of the acquisition the probability
for each class is calculated by dividing the sampling frequency by the total number of samples. The
result is the sound level distribution of probabilities shown.
After this, the cumulative distribution is calculated. This is based on the sound level distribu-
tion of probabilities, beginning with a 100% probability for all lower classes with a value lower
than the minimum measured level and for each class progressively subtracting the corresponding
distribution probability of the level probabilities.
The cumulative probability will be null for levels higher than the maximum measured level.
The percentile levels are calculated interpolating the cumulative distribution.
For example, if from the analysis of the noise of a traffic road you detect that, the sound level (usu-
ally A weighted, examining the auditory impact), remains higher than 74dB half the time, the per-
centile level L
50
is 74dB.
The integrating sound level meters directly supply the time integrated parameters, such as
equivalent level and sound exposure level, in addition to maximum and minimum. On the other
hand, the statistical analysis is a prerogative of statistical analyzers.