Abstract: The Speech Transmission Index (STI) is an objective measure that predicts speech intelligibility. Test signals are played back through a channel under test. An STI analyzer at the channel output calculates an index between 0 and 1, indicating intelligibility. Over the years, various test signals have been used for measuring the STI, all based on the same principles but differing in the modulation frequencies tested and octave bands covered by the signal. The invention disclosed is a new method for constructing test signals: not just the transfer of modulations on a carrier signal is analyzed, but also the carrier signal itself This apprach leads to more accurate STI measurements that correspond more closely to the ideal (theoretical) STI and to subjective speech intelligibility. Shorter measuring times are achieved without compromising the accuracy of the measurement, while extending the range of systems to which the STI can be reliable applied.

Abstract: System for giving intelligibility feedback to a speaker (1), speaking for an audience (2), comprising a first microphone (3) at the speaker's side and a second microphone (4) at the audience's side. Both microphones are connected to processing means (5) which are arranged to compute an intelligibility value based on both microphones' signals. Signalling means (6), preferably at the side of the audience, are arranged to generate an intelligibility feedback signal depending on the calculated intelligibility value. The signalling means being arranged to generate said intelligibility feedback signal in an optical form, visible for the speaker concerned. Wireless connection means (19) may interconnect the microphones, the processing means and the signalling means.