UNI EN ISO 9921 : 2004

Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Descriptions of speech communications
  4.1 General
  4.2 Speaker
  4.3 Transmission channel
  4.4 Listener
5 Performance of speech communications
  5.1 General
  5.2 Alert and warning situations
  5.3 Person-to-person communications
  5.4 Public address in public areas
  5.5 Personal communication systems
  5.6 Summary of recommended minimum performance
6 Assessment and prediction
  6.1 General
  6.2 Subjective assessment methods
  6.3 Objective assessment and prediction methods
Annex A (normative) Speaker and listener characteristics
Annex B (informative) Subjective speech-intelligibility
                      tests
Annex C (informative) Speech transmission index, STI
Annex D (informative) Overview of the means of
                      communication and related parameters
Annex E (normative) Speech interference level, SIL
Annex F (informative) Intelligibility ratings for
                      speech communications
Annex G (normative) Definition of symbols
Annex H (informative) Examples of applications of
                      predictive intelligibility methods
Bibliography

Specifies the requirements for the performance of speech communication for verbal alert and danger signals, information messages, and speech communication in general.