people are involved, other probabilities hold. It is interesting but not astonishing that STI prediction is independent of the language spoken – not astonishing, as the ability of the channel to transport patterns of physical speech is measured. Another method is defined for computing a physical measure that is highly correlated with the intelligibility of speech as evaluated by speech perception tests given a group of talkers and listeners. This measure is called the Speech Intelligibility Index, or SII. Nominal qualification bands for STI The IEC 60268-16 ed4 2011 Standard defines a qualification scale in order to provide flexibility for different applications. The values of this alpha-scale run from "U" to "A+". Standards STI has gained international acceptance as the quantifier of channel influence on speech intelligibility. The International Electrotechnical Commission Objective rating of speech intelligibility by speech transmission index, as prepared by the TC 100 Technical Committee, defines the international standard. Further the following standards have, as part of the requirements to be fulfilled, integrated testing the STI and realisation of a minimal speech transmission index: International Organization for Standardization (ISO) standard for sound system loudspeakers in Fire detection and fire alarm systems National Fire Protection Association Alarm Code British Standards Institution Fire detection and alarm systems for buildings German Institute for Standardization Sound Systems for Emergency Purposes STIPA STIPA (Speech Transmission Index for Public Address Systems) is a version of the STI using a simplified method and test signal. Within the STIPA signal, each octave band is modulated simultaneously with two modulation frequencies. The modulation frequencies are spread among the octave bands in a balanced way, making it possible to obtain a reliable STI measurement based on a sparsely sampled Modulation Transfer Function matrix. Although initially designed for Public Address systems (and similar installations, such as Voice Evacuation Systems and Mass Notification Systems), STIPA can also be used for a variety of other applications. The only situation in which RASTI is currently considered inferior to full STI is in the presence of strong echoes. A single STIPA measurement generally takes between 15 and 25 seconds, combining the speed of RASTI with (nearly) the wide scope of applicability and reliability of full STI. Since STIPA has become widely available, and given the fact that RASTI has several disadvantages and no benefits over STIPA, RASTI is now considered obsolete. Although the STIPA test signal does not resemble speech to the