Speech Intelligibility STIPA Tests

Announcements made in public places such as classrooms, auditoriums, shopping malls, stadiums, train stations, airports, concert halls or similar places should be well understood by the audience. It is very important to clearly inform people in danger of escape instructions, especially in an emergency. It is therefore essential to verify speech intelligibility in these places using a repeatable and accurate method.

In short, STI is the speech transmission index and is the most widely accepted standardized parameter for assessing the intelligibility of a spoken message.

Speech intelligibility is determined by reproducing a known signal (STIPA test signal) and measuring the quality of this signal when it reaches each measurement position. A standard based on these measurements is the following standard published by the International Electrotechnical Commission (IEC): IEC 60268-16 Sound system equipment - Part 16: Objective assessment of speech intelligibility according to the speech transmission index.

This standard defines the STI model and test signals, measurement and estimation methods. The purpose of this standard is to provide comprehensive guidance for all users of the STI model in the fields of sound, communications and acoustics. This standard does not provide STI criteria for certification of transmission channels, eg voice alarm system, but some typical application values ​​are included in the annex to the standard (Annex G). Each measurement method has its limitations and the reader refers to clauses related to limitations such as speech privacy, echo and systems using digital audio compression.

Briefly, this standard defines for STI how any distortion in the signal is measured and how the intelligibility result is evaluated as a single number from 0 (incomprehensible) to 1 (perfect intelligibility).

Speech intelligibility is a measure of how clearly a person speaks so that his speech can be understood by the other person. Low speech intelligibility causes misunderstandings and loss of interest.

Factors that affect speech intelligibility include:

• sound pressure level
• Ambient noise level
• Reverberation time
• If a public address (PA) system is used, the frequency response of that system (for example, too much bass)
• Signal-to-noise ratio (ie quality of the PA system)

Our organization also provides speech intelligibility STIPA testing services with its trained and expert staff and advanced technological equipment, among the numerous test, measurement, analysis and evaluation studies it provides for businesses in various sectors.