ISO 9921:2003规定了语音警报和危险信号、信息信息信息和一般语音通信的语音通信性能要求。描述了在实际应用中预测和评估性能的方法，并给出了实例。

ISO 9921:2003 specifies the requirements for the performance of speech communication for verbal alert and danger signals, information messages, and speech communication in general. Methods to predict and to assess the performance in practical applications are described and examples are given.