A revised speech spectrum for STI calculations

The ability of the Speech Transmission Index (STI) to predict speech intelligibility under noisy conditions is highly dependent on the assumed spectrum of the speech signal. Examination of the literature showed that the long-term average speech spectrum of male talkers differs substantially from the speech spectrum recommended for STI calculations (IEC 60268-16). To explore these issues, the long-term average speech spectrum of forty male British English people was first measured, compared with the available literature and proposed for STI calculations. Then, using several voice alarm systems, the influence of the measured spectrum on STI calculations was assessed and comparisons made with the standard speech spectrum. The results showed significant STI differences under noisy conditions and considerable reductions in the required electrical power with the use of the new proposed male spectrum. This indicated that the current STI method could benefit from a revised speech spectrum

Does 1/3rd octave equalisation improve the sound in a typical cinema?

This paper continues the investigation into the current poor state of sound in cinemas. Specifically, it investigates the viability of the specified Dolby equalisation of cinema sound systems and whether it enhances the aural experience. Much is still spoken and written about ‘room equalisation’, but, in reality, the concept is a myth. Rooms cannot be equalised. Sound waves expand three-dimensionally and interact with the boundaries of rooms in complex ways causing the frequency response at every point in any non-anechoic room to be different in both level and spectrum with a given source. Using acoustic measurements conducted in a cinema style room using a loudspeaker, we demonstrate how attempts to equalise the response for a given position in a room will not necessarily produce improvements at the majority of other places within the room. Responses were measured with different time-window lengths to assess the changes in the received spectra over time. Comparison is also made between two loudspeakers with different directivity characteristics, which show that the response at each location is highly dependent on the way in which the loudspeaker excites the room