IEC 60268-16:2011

FOREWORD
INTRODUCTION
1 Scope
2 Normative references
3 Terms and definitions
4 Description of the STI method
5 Direct method of measuring STI
6 Indirect method of measuring STI using the impulse
  response
7 Measurement procedures, post-processing of data
  and applications
8 Use of STI as a design prediction tool
Annex A (normative) - Speech transmission index
        (STI) and revised STI methods
Annex B (normative) - STIPA method
Annex C (normative) - STITEL method
Annex D (informative) - RASTI method (obsolete)
Annex E (informative) - Qualification of the STI and
        relationships with other speech intelligibility
        measures
Annex F (informative) - Nominal qualification bands for STI
Annex G (informative) - Examples of STI qualification bands
        and typical applications
Annex H (informative) - Non-native listeners
Annex I (informative) - Effect of age-related hearing loss
        and hearing impairment on speech intelligibility
Annex J (normative) - Calibration of STI test signal level
Annex K (informative) - Example test report sheet for STI
        measurements
Annex L (normative) - Prediction of STI using statistical
        methods
Annex M (informative) - Adjustments to measured STI
        and STIPA results for simulation of occupancy
        noise and different speech levels
Annex N (informative) - Other methods of determining
        speech intelligibility
Bibliography

IEC 60268-16:2011 specifies objective methods for rating the transmission quality of speech with respect to intelligibility. It provides a comprehensive manual for all types of users of the STI method in the fields of audio, communications and acoustics. Three methods are presented, which are closely related and are referred to as STI, STIPA, and STITEL. The first two methods are intended for rating speech transmission performance with or without sound systems. The STITEL method has more restricted uses. This fourth edition cancels and replaces the third edition, published in 2003, and constitutes a technical revision. It includes the following significant technical changes with respect to the previous edition:
- development of more comprehensive, complete and unambiguous standardization of the STI methodology;
- the term STIr is discontinued. A new function for the prediction of auditory masking effects is introduced;
- the concept of 'speech level' and the setting of the level of the test signal have been introduced;
- additional information has been included on prediction and measurement procedures. The French version of this standard has not been voted upon.