• Disagreement between STI and STIPA measurements due to high level, discrete reflections

      Hammond, Ross; Mapp, Peter; Hill, Adam J.; University of Derby; Peter Mapp Accosiates (Audio Engineering Society, 2017-05-21)
      Objective measures of intelligibility, speech transmission index (STI) and speech transmission index for public address systems (STIPA), often form the basis for sound system verification. The reported work challenges the accuracy of both measures when encountering high level, discrete reflections. Tests were carried out in an anechoic environment with artificial reflections added between 0 and 500ms. Discrepancies were found to occur above 80ms due to synchronisation between modulation frequencies and reflection arrival times. Differences between STI and STIPA of up to 0.1 were found to occur for the same delay condition. Results suggest STIPA should be avoided in acoustic environments where high level, discrete reflections occur after 80ms and STI should only be used alongside other verification methods.
    • The influence of discrete arriving reflections on perceived intelligibility and speech transmission index measurements

      Hammond, Ross; Mapp, Peter; Hill, Adam J.; University of Derby; Peter Mapp Associates (Audio Engineering Society, 2016-09-20)
      The most widely used objective intelligibility measurement method, the Speech Transmission Index (STI), does not completely match the highly complex auditory perception and human hearing system. Investigations were made into the impact of discrete reflections (with varying arrival times and amplitudes) on STI scores, subjective intelligibility, and the subjective “annoyance factor.” This allows the effect of comb filtering on the modulation transfer function matrix to be displayed, as well as demonstrates how the perceptual effects of a discrete delay cause subjective “annoyance,” that is not necessarily mirrored by STI. This work provides evidence showing why STI should not be the sole verification method within public address and emergency announcement systems, where temporal properties also need thoughtful consideration.
    • The influence of discrete arriving reflections on perceived intelligibility and STI measurements

      Hammond, Ross; Mapp, Peter; Hill, Adam J.; University of Derby; Peter Mapp Associates (Audio Engineering Society, 2016-05-26)
      The most widely used objective intelligibility measurement method, the Speech Transmission Index (STI), does not completely match the highly complex auditory perception and human hearing system. Investigations were made into the impact of discrete reflections (with varying arrival times and amplitudes) on STI scores, subjective intelligibility, and the subjective annoyance factor.’ This allows the effect of comb filtering on the modulation transfer function matrix to be displayed, as well as demonstrates how the perceptual effects of a discrete delay cause subjective ‘annoyance,’ that is not necessarily mirrored by STI. This work provides evidence showing why STI should not be the sole verification method within public address and emergency announcement systems, where temporal properties also need thoughtful consideration.
    • Investigation into the relationship between standing audience density and absorption.

      Hammond, Ross; Hill, Adam J.; Mapp, Peter; University of Derby; Peter Mapp Associates (Institute of Acoustics, 2018-11)
      Predicting acoustics of occupied performance venues is problematic due to difficulties in the selection of accurate audience absorption coefficients. The absorption due to a small group of people measured in a reverberation chamber cannot be accurately transferred to larger audiences due to differences between area to edge ratio. Analysis of data from an FDTD acoustic model of a reverberation chamber with an audience modelled as columns distributed at different densities with various perimeter to area ratios, allows derived absorption coefficients to be transferable to larger audience sizes. For densely-packed audiences, diffraction results in low frequencies having linear correlation between audience size and total absorption. There is less increase in total absorption per person at higher frequencies. Comparable real-world measurements confirm these findings, allowing the verified absorption coefficients to be applied to an acoustic model of a performance venue to inspect audience effects on absorption for typical configurations.