SPEECH INTELLIGIBILITY
MEASUREMENT SYSTEMS

Equipment You Need To Accurately
Measure The Intelligibility Of Voice
Enunciator and Voice Evacuation Systems
With STICistm Software

  • 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

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INTELLIGIBILITY SYSTEM COMPONENTS

DSP2B

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

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

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.spacer52.gif - 248 Bytes

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.
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.
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.
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.

The Measurement of Speech Intelligibility
The draft version of the new ISO 9921 standard on the "Assessment of Speech Communication" defines speech intelligibility as: "a measure of effectiveness of understanding speech". This contribution describes and compares several of these measures for determining the intelligibility of a given speech transmission system. It may include the acoustical environment at the speaker and the listener position.
In general two principally different assessment methods may be applied:
(1) Subjective assessment, based on the use of speakers and listeners,
(2) Objective assessment based on physical parameters of the transmission channel.
A paper discussing "The Measurement of Speech Intelligibility" can be downloaded here.

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STI Product Information Brochure. 639K.
Understanding Speech Intelligibility White Paper. 223K. This white paper is provided through the courtesy of Bose® Professional Systems.
DSP30 and Test Results White Paper. 49K. This white paper is provided through the courtesy of Bose® Professional Systems and TNO Human Factors.
The Measurement of Speech Intelligibility White Paper. 203K. This white paper is provided through the courtesy of TNO Human Factors.
DSP30 approval letter. 15K.