Increasing Robustness in the Calculation of the Speech Transmission Index from Impulse Responses

Abstract

There are many factors that can affect the measured values of the speech transmission index (STI), and this paper examines how and why identical inputs into STI calculation software are yielding varying results. The study involved a survey of a number of software implementations of the Indirect Method for computing the STI from an impulse response, one of which was written by the authors. Results are presented for artificial and measured impulse responses, and for signal and noise spectra that were designed to test particular aspects of the STI calculation. While most deviations between implementations were within 0.01 STI, some were not, revealing a need for greater robustness in the design of software and greater clarity in the STI standard (IEC60268-16), including more support for validation. This paper provides some data for such validation.

References

Katz

B.F.G.

, International round robin on room acoustical impulse response analysis software 2004, Acoustics Research Letters Online (ARLO), 2004, 5(4), 158–164.

IEC 50268-16 Ed. 4, Sound System Equipment – Part 16: Objective Rating of Speech Intelligibility by Speech Transmission Index, International Electrotechnical Commission 2011.

ISO 3382-3: 2013: Acoustics – Measurement of room acoustic parameters – Part 3: Open plan offices, International Organization for Standardization, 2013.

AS 1670.4-2004: Fire detection, warning, control and intercom systems – System design, installation and commissioning – Sound systems and intercom systems for emergency purposes, Standards Australia, 2004.

van Wijngaarden

Verhave

, and Steeneken

, The speech transmission index after four decades of development, Acoustics Australia, 2012, 40(4), 134–138.

IEC 50268-16 Ed. 3, Sound System Equipment – Part 16: Objective Rating of Speech Intelligibility by Speech Transmission Index, International Electrotechnical Commission 2003.

Schroeder

, Modulation transfer functions: Definition and measurement, Acustica, 1981, 49(3), 179–182.

Venturi

Farina

, and Tronchin

, On the effects of pre-processing of impulse responses in the evaluation of acoustic parameters on room acoustics, Journal of the Acoustical Society of America, 2013, 133(5), 3224 (POMA 19, 015006).

Guski

, and Vorländer

, Comparison of noise compensation methods for room acoustic impulse response evaluations, Acta Acustica united with Acustica, 2014, 100, 320–327.

10.

Cabrera

Lee

Collins

Hartmann

Martens

W.L.

, and Sato

, Variation in oral-binaural room impulse responses for horizontal rotations of a head and torso simulator, Building Acoustics, 2011, 18(1–2), 227–252.

11.

Chu

W.T.

, and Warnock

A.C.C.

, Detailed directivity of sound fields around human talkers. Institute for Research in Construction, National Research Council of Canada, Ottawa, ON, Canada, Technical Report IRC-RR-104, 2002.

12.

IEC 61260 Ed. 1, Electroacoustics – Octave-band and fractional-octave-band filters, International Electrotechnical Commission 1995.

13.

Park

S. K.

, and Miller

K. W.

, Random number generators: Good ones are hard to find, Communications of the ACM, 1988, 31, 1192–1201.

14.

Cabrera

Jimenez

, and Martens

W.L.

, Audio and Acoustical Response Analysis Environment (AARAE): A tool to support education and research in acoustics, Proceedings of Internoise, Melbourne, Australia, 2014.