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Title:Private audio delivery in reverberant spaces
Author(s):Liu, Yu-Jeh
Advisor(s):Dokmanic, Ivan
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):sound zone
sound focusing
private audio
null space
inverse problem
room acoustics
loudspeaker array
Abstract:We study the problem of delivering private audio to multiple users in a reverberant room. New methods are proposed which work with specially designed noise signals and make constructive use of reverberation. First, traditional sound zones problem formulation is introduced. In this formulation, a loudspeaker array is used to create isolated soundfields as designated by the user. Traditional approaches such as acoustic contrast control (ACC) and pressure matching (PM) were devised as solutions to the sound zones problem, and they were proven to be effective. One aspect that has not been addressed by these methods is the privacy/security issue. With eavesdroppers present in the room, traditional approaches to sound zones problems do not ensure secure delivery of audio that prevents the eavesdroppers from comprehending the contents. Next, new methods are thus introduced which address the added privacy requirement. Instead of considering reverberation as unwelcome, the proposed formulation takes advantage of the multi-path nature and leverages the random-like echoes to simultaneously achieve sound focusing and eavesdropping prevention. Two methods are introduced. The first one is based on direct least-squares optimization; we refer to it as the Least-Squares (LS) method. The second one, adopted from the wireless communication literature, exploits the null space of the multiple-input-multiple-output channel matrix; we refer to it as the Null Space (NS) method. The two methods are evaluated and compared in numerical and real-world experiments. Both methods are shown to achieve sound focusing as well as very low signal-to-noise ratio (SNR) outside the focusing spots. The NS method provides sharper intelligibility drop which results in smaller, more spatially refined sound focusing spots. Subject to the usual limitations of sound zone methods such as long computation time or the requirement to know the impulse responses, both methods are proven to provide new solutions to sound zone problems with privacy constraints.
Issue Date:2020-05-11
Rights Information:Copyright 2020 Yu-Jeh Liu
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05

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