# An Estimation of Speech Privacy Class Based on ISO Parameter  
[PERSON]  
School of Electrical Engineering, University of Belgrade, Bulevar Kralja Aleksandra 73, 11120 Belgrade, Serbia; [EMAIL_ADDRESS] (TM. ); [EMAIL_ADDRESS] (M.M. ); [EMAIL_ADDRESS] (D.S.P.) [PERSON]  
School of Electrical Engineering, University of Belgrade, Bulevar Kralja Aleksandra 73, 11120 Belgrade, Serbia; tm@etf. levels defined on a scale of perception. It is also a reality that ensuring sound comfort in buildings involves administrative aspects, encompassing house rules and even legal and regulatory documents [12; 16]. Nevertheless, the primary arena for seeking solutions to guarantee sound comfort and privacy, as its paramount dimensions, lies in the domain of construction and technical measures defined by the building project and subsequently implemented during construction. One crucial step in ensuring privacy is preventing the recognition of speech from neighboring rooms [17]. In modern engineering practice, the challenge of recognizing speech within the same room has become increasingly prevalent, particularly in open-space offices [18]. In the building design process, privacy is typically addressed indirectly through the selection of partition structures (walls, ceilings, doors, windows) and their insulating properties [19]. However, many design analyses focus solely on assessing the minimum required value of the sound reduction index (\(R\)) for partitions in relevant positions within the building, often without broader consideration of the context in which these partitions will be situated [20]. While attenuating sounds through the insulating properties of partitions is one aspect of ensuring privacy, an equally important aspect is understanding the ambient noise levels in spaces where privacy is sought [21]. The explanation of the physical process compromising privacy is rooted in the fundamental principles of telecommunications, where the consideration of the signal-to-noise ratio (\(SNR\)) is paramount [22]. This concept equally applies to spoken communication within the acoustic domain. The term'signal' refers to the acoustic speech signal with all its dynamic nuances, while 'noise' denotes ambient noise present in the listener's environment [23]. The distinction from telecommunications lies in the fact that the ability to 'extract' a speech signal from noise is determined by the inherent limitations of the sense of hearing and cannot be enhanced. The literature has demonstrated that the \(SNR\) at the listener's location governs the audibility and intelligibility of speech [24]. This implies that the environment in which speech is heard plays a crucial role in determining privacy [25]. Due to the dynamic characteristics of the speech signal, its signal-to-noise ratio is a complex, time-varying quantity that can only be discussed statistically [26]. It has been demonstrated that speech becomes unintelligible when the mean value of the \(SNR\) across \(1/3\) octave bands drops to approximately \(-2\) dB [25; 27]. This relationship is particularly evident in the frequency range crucial for speech, spanning from the \(1/3\) octave band with a central frequency of \(160\) Hz to the \(5\) kHz range. Research related to speech privacy in the literature primarily refers to office buildings, meeting rooms and open-plan offices [28; 29]. Some research specifically looks at user satisfaction with speech privacy [14]. Research on speech privacy measurements in buildings can be found [30], as well as studies on speech privacy prediction [31]. In the literature, various solutions for quantifying the state of speech privacy are reported [32]. The speech transmission index (\(STI\)) is a well-known measure of intelligibility, most suited to the evaluation of speech intelligibility in rooms, with stimuli subjected to additive noise and reverberance [33; 34]. However, the \(STI\) measure suffers from the problem of being poorly correlated to the subjectively measured intelligibility of stimuli subjected to nonlinear processing [35].