13.4 STIPA MEASUREMENT AND CALCULATION PROCESS
STI measurements usually relate to objects (buildings), which may consist of several areas (rooms) in which
measurements are made in a given number of points (in practice, from 1 up to several dozen). In addition,
especially in case of assessing speech intelligibility in a room on the directly, i.e. without an amplification system,
tests are performed for a given number of source positions (in practice from one to several). It may happen that
a given area is examined in several configurations - e.g. a theatre hall with a raised and lowered curtain, or a
rail vehicle at a standstill and while moving. The result for a given point is obtained on the basis of several
measurements (in practice from 1 to 6) - most often as an average value. Analyses are performed independently
for areas in a given configuration.
The STIPA function enables measuring and calculating the next results:
• STI - Speech Transmission Index representing the transmission quality of speech with respect to
intelligibility by a speech transmission channel, ranging between 0 and 1. STI is calculated for individual
measurements and averaged for the measurement point and for the area.
•
Δ – difference between maximum and minimum values of STI index obtained for the measurement point
of the tested area.
• LAeq – A weighed time-averaged sound level for 15-seconds integration period, in dB.
•
LCeq – C weighed time-averaged sound level for 15-seconds integration period, in dB.
•
LZeq – Z weighed time-averaged sound level for 15-seconds integration period, in dB.
• LAS – time weighted sound level expressed at observation time (15-seconds integration period), in dB.
•
m(f1), m(f2) - modulation transfer ratios as a function for two modulation frequency per each of 7 octave
bands, ranging between 0 and 1.
• CIS - Common Intelligibility Scale
.
• σ - standard deviation of measured STI indexes for the tested area.
• Min – minimal STI value obtained within measurements.
There are some additional indications:
• The STI qualification band: A+ trough U (see Annex G to IEC 60268-16:2011).
• Errors detected during measurements and calculation of STI indexes.
These results are displayed in different views:
• Area view - main STIPA view that allows you to create new measurement points, delete measurement
points or exclude them from the calculation of averaged indexes for the Area as well as to go to the Point
view for the selected point. This view presents a list of measurement points and next results:
o Averaged STI (or CIS) index with consideration of the Ambient noise
distortions (Avg.) and STI spread (
Δ) for the tested area.
o
Averaged STI (or CIS) indexes with consideration of the Ambient
noise distortions (STI) and STI spreads (Δ) for measurement points.
o
The STI qualification band (A+ through U) and error indication is
displayed for each measurement point.
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