- Now Intelligibility Can Be Measured
- STICistm system used at New England Patriot's Gillette
Stadium. Click here to read about it.
- Meets or Exceeds International Standards
- Test CD Developed by TNO Human Factors in Holland - Developer of STI
in Europe
- DSP2, DSP30 Analyzers and companion TALKBOX Signal Generator
INTELLIGIBILITY SYSTEM COMPONENTS
DSP2B - Dedicated Speech Intelligibility Meter
Measures Sound Pressure Level and Speech Intellegibility Index in CIS, STI,
or RASTI formats using the OPTion STICistm Software. |
DSP30B / DSPCIB - Full
Function Stand Alone Audio Spectrum Analyzers Measure Sound Level and Speech
Intellegibility Index in CIS, STI, or RASTI formats when used with OPTion
STICistm Software. (DSP30B Shown.) |
TALKBOX - Signal Generator - An Integral Part of
The Speech Analysis System - Used with either DSP2B, DSP30B or DSPCIB -
Applies Specialized Test Tones To A Voice Message System. |
Major International, European, and North American fire alarm codes now
require that voice alarm systems meet minimum levels of speech
intelligibility. The new codes and standards have spawned the need for
education about the basics of intelligibility, and for tools to ensure that
voice alarm systems are designed for good intelligibility, can be measured
for compliance at the time of commissioning, and can be periodically tested
during the life of the system.
The basics of speech intelligibility,
including the factors that affect intelligibility in typical situations are
reviewed in a white paper presented at the National Fire Protection
Association Congress by Bose® Professional Systems.
In addition, the various methods for measuring speech intelligibility are
discussed, together with techniques for predicting intelligibility in
advance of building construction or equipment installation. Finally, many of
the practical considerations fire alarm professionals will face in managing
the intelligibility requirement are presented.
To obtain a copy of this white paper, you can download it here.
Improving the Intelligibility of
Safety and Security Announcements Using the DSP with OPTion STICistm
| WHAT IS INTELLIGIBILITY? |
| Speech intelligibility is not a physical quantity like Amperes, Volts,
or BTU's. It is the degree to which we understand spoken language. Speech is
not necessarily intelligible simply because it is audible. Everyone has
experienced speech signals that are loud enough but overly reverberant,
suffer from echoes or distortion and therefore are not understandable.
Announcements in airports, train stations and places of worship often suffer
from this problem. |
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| MEASURING INTELLIGIBILITY WITH STI |
| The Speech Transmission Index (STI) is a quantitative method of
measurement covered in the International Electrotechnical Commission (IEC)
standard 60268-16. |
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| SPEECH TRANSMISSION INDEX (STI) METHOD |
| The military and others began funding the research and development of a
quantitative method of measuring speech intelligibility that could measure a
system that had virtually any combination of the factors commonly found to
affect speech intelligibility. The work that eventually led to what is now
called the Speech Transmission Index method was started in the 1970's at a
well-known research laboratory called TNO Human Factors in the Netherlands,
mainly under NATO funding. The method developed proved robust under a wide
array of conditions from a talker in a room to a telephone system to an area
PA system. The STI method has been implemented in a number of commercially
available devices and is today an international standard used extensively
throughout the world. The STI method has an advantage in that it correctly
accounts for all of the factors in the talker-to-listener transmission path
that affect intelligibility. The method is based on replacing speech with a
repeatable signal that has the same characteristics as actual speech. |
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| MODEL DSP30 WITH THE STICistm INTELLIGIBILITY OPTION |
Until now, the routine measurements of intelligibility necessary to
enforce the codes and
standards were difficult to make. With this problem in
mind, we set out to develop a dedicated instrument that would accurately
measure speech intelligibility according to international standards, and do
so quickly and simply, thus making it possible for experts and non-experts
alike to quickly measure intelligibility. Their results show clearly the
feasibility of such an instrument.
The DSP30 is a DSP-based 1/3 octave
audio spectrum analyzer and sound pressure level
meter. The analyzer is
handheld, can be battery operated and is extremely easy to use. In addition,
the DSP30 can be enhanced with a series of software/hardware options. For
measuring intelligibilty, Option STICistm is available.
This option includes the STI-PA signal developed by TNO Human Factors in
the Netherlands where the STI method was researched and developed. The STI-PA
signal, contained on an audio CD, is input to the system under test.
STI measurements can be made by most without significant training. Once
the STI-PA signal has been input to the system under test, a single button
push on the DSP30 will produce the STI, converted to the Common
Intelligibility Scale as specified in IEC standard 60849, in about 15
seconds. The STI-PA signal can be left continuously playing, making it
possible to simply move the DSP30 to a new position and a new measurement
initiated.
The DSP30 with STICistm software was
tested to ensure that it behaved according to theory and met the goals for
accuracy, portability, and simplicity. STI values obtained on the meter were
compared to STI values obtained using the full 98 combinations of modulated
noise as calculated on a reference system at TNO. A number of representative
test conditions were used, including different bandpass conditions, noise
levels, non-linear effects, reverberation and echo profiles. The results are
shown in a white paper presented at the Reproduced Sound 17 Conference . The
data show conclusively that the meter is accurate in a wide range of
conditions typical of public address systems.
You can download a copy of this white paper here.
Our equipment and software has been approved by TNO for the
objective prediction of speech intelligibility.
You can download a copy of this letter here. |
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