38 Bedrock SMxx operating manual © Bedrock Audio BV, 2019
39
7.5. Statistical acoustics (percentiles)
This module is designed to create insight into the statistical distribution of sound levels
during the measurement period. In particular, it give percentile levels: the level exceeded
during the measurement period for a specific percentage of the time. Percentile levels are
commonly indicated with letter L (for level) followed by the percentile threshold, e.g. L95
being the level that is exceeded 95% of the time during the measurement period. and L10
the level that is exceeded only 10% of the time. Logic dictates the L95 normally has a lower
value than L10; for a perfectly steady-state signal, L95 and L10 will both be equal to LEQ.
The L% module offers the same frequency weightings and time averaging options as the
“standard” sound level meter module (A, C, Z; FAST, SLOW).
The operation and specifications of sound level meters are very specifically
and precisely determined by IEC-61672-1:2013. However, there is current-
ly no international standard that governs how the additional parameters
that come into play with percentile-levels should be chosen. Implementa-
tions by various manufacturers, while these appear to be consistent on the
surface, may differ. The procedure adopted by the Bedrock SMxx is explic-
itly defined further on in this chapter.
The module is capable of simultaneously measuring and displaying sound pressure levels
with six different sets of settings: three displayed on the left (“main”) and three displayed
on the right (“auxiliary”).
Percentile settings (including Min, Max, EQ, Peak, Current) can be chosen by pressing the
level field, in which case a keyboard appears
Statistical acoustics module, showing levels for six different sets of settings (left). The percentile
selections can be chosen through a keyboard that appears when pressing the level fields (right).
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