Archives of Acoustics, 47, 2, pp. 191-199, 2022

Effect of Power Amplifier Distortion on the Speech Transmission Index for Public Address Systems

Wrocław University of Science and Technology

The effect of the power amplifier on speech intelligibility in public address systems is often marginalised – i.e. it is assumed that it does not introduce significant signal distortion. This approach is justified when the linear range of the amplifier is used. The large crest factor of the speech signal and economic considerations mean that the amplifier also works in the non-linear range. In this paper, the effect of power amplifier distortion on the speech transmission index for public address systems (STIPA) is presented. In the first step, this influence was evaluated by measurements for Class AB and D amplifiers. Then, a computer model of the public address system based on the direct STIPA method, taking into account the non-linear properties of the amplifier, was proposed. Using the computer model, the optimum amplifier driving values were determined taking into account the reverberation time and interfering noise.
Keywords: speech transmission index; power amplifier; public address system.
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Ballou G.M. [Ed.] (2015), Handbook for Sound Engineers,

th ed., Focal Press, doi: 10.4324/9780203758281.

Brachmański S. (2015), Selected issues of quality assessment of speech signal transmission [in Polish], Oficyna Wydawnicza Politechniki Wrocławskiej, Wrocław.

CEN/TS 54-32 (2015), Fire detection and fire alarm systems. Planning, design, installation, commissioning, use and maintenance of voice alarm systems.

Chasin M., Russo F.A. (2004), Hearing aids and music, Trends in Amplification, 8(2): 35–47, doi: 10.1177/108471380400800202.

Dobrucki A. (2011), Nonlinear distortions in electroacoustic devices, Archives of Acoustics, 36(2): 437–460, doi:

Dziechciński P. (2019), A computer model for calculating the speech transmission index using the direct STIPA method, Vibrations in Physical Systems, 30(1): 1–8.

Dziechciński P. (2014), Audio and sound level monitoring in electroacoustic systems, Signal evaluation and monitoring in sound engineering, [in:] Audio Engineering Society – Polish Section, Dobrucki A. [Ed.], pp. 39–48, Wrocław.

ECMA TR/105 (2012), A Shaped Noise File Representative

of Speech.

European Commission (2014), Commission Regulation (EU) No 1300/2014 (2014) on the technical specifications for interoperability relating to accessibility of the Union’s rail system for persons with disabilities and persons with reduced mobility.

Houtgast T., Steeneken H.J.M. (1973), The Modulation Transfer Function in rooms acoustics as a predictor of speech intelligibility, The Journal of the Acoustical Society of America, 54(2): 557, doi: 10.1121/1.1913632.

Houtgast T., Steeneken H.J.M., Plomp R. (1980), Predicting speech intelligibility in rooms from the modulation transfer function. I. General room acoustics, Acta Acustica united with Acustica, 46(1): 60–72.

IEC 60268-2 (1987), Sound system equipment – Part 2: Explanation of general terms and calculation methods.

IEC 60268-3 (2018), Sound system equipment – Part 3: Amplifiers.

IEC 60268-10 (1991), Sound system equipment – Part 10: Peak programme level meters.

IEC 60268-16 (2020), Sound system equipment – Part 16: Objective rating of speech intelligibility by speech transmission index.

ITU-R BS.1770-4 (2015), Algorithms to measure audio programme loudness and true-peak audio level.

Levanen T., Talvitie J., Renfors M. (2012), Performance evaluation of time-multiplexed and datadependent superimposed training-based transmission with practical power amplifier model, EURASIP Journal on Wireless Communications and Networking,

(1): 1–19, doi: 10.1186/1687-1499-2012-49.

Licklider J.C.R. (1946), Effects of amplitude distortion upon the intelligibility of speech, The Journal of the Acoustical Society of America, 18(2): 429–434, doi: 10.1121/1.1916383.

Licklider J.C.R., Pollack I. (1948), Effects of differentiation,

integration, and infinite peak clipping upon the intelligibility of speech, The Journal of the Acoustical Society of America, 20(1): 42–51, doi: 10.1121/1.1906346.

Rapp C. (1991), Effects of HPA-nonlinearity on a 4-DPSK/OFDM-signal for a digital sound broadcasting system, [in:] Proceedings of 2nd European Conference on Satellite Communications, pp. 179–184, Liege.

Steeneken H.J.M., Houtgast T. (2002), Validation of the revised STIr method, Speech Communication, 38(3–4): 413–425, doi: 10.1016/S0167-6393(02)00010-9.

DOI: 10.24425/aoa.2022.141649

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