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98 Speech Intelligibility
STI-PA testing
Models SE and DL
Speech Intelligibility
Another available add-on feature is Speech Transmission Index (STI) used to
evaluate and classify speech intelligibility dependent of background noise level. STI
is the standardized measurement in the IEC 60268-16:1998 standard.
STI-PA testing
STI refers to the amount of modulation preserved in the broadcasting of an artificial
speech signal through an alarm system. The intelligibility measurement is a single
value between zero and one, which factors in corruption of speech, with modulating
speech frequencies over octave bands between 125Hz to 8kHz.
STI-PA is measured using seven octave bands and 2 modulation indices per octave
band simultaneously allowing a 15 second measurement. In essence, any noise
which masks (or corrupts) the talker-to-listener path is evaluated and a recommended
measurement is computed at the end of an intelligibility test. The following sections
briefly address points to consider when setting up a STI-PA test.
Zones
Where do I measure speech intelligibility?” A building or stadium can be
broken into “zones”. Each “zone” has a room with one alarm system. In
some situations, one room may have more than one alarm system or may
have a change in ceiling height (such as an atrium or a balcony seating
versus lower level seating). In those instances, each section would be
considered a zone and each zone would be tested.
After determining the “zones” in your building, it is recommended to design a
map of the key zones/rooms. Generally, a zone is a 20X20 area. If the room
is larger than 20X20, it is recommended to take another measurement in this
section.
Selecting STI scale or CIS scale
With the SoundPro, you have two measurement options which will determine the
intelligibility of your building which are the STI scale and the CIS scale (explained
below.)