Depuis 2002, la directive européenne 2002/49/CE demande aux grandes villes de définir des zones calmes dans leur P.P.B.E. (Plan de Prévention du Bruit dans l'Environnement) dans le but de les préserver. L'utilisation de l'indicateur acoustique Lden est suggérée mais les états membres sont libres d'en proposer d'autres. Afin d'aider les autorités en charge de l'application de cette directive, ce travail de thèse propose une approche multidisciplinaire pour mieux définir cette notion de zone calme en milieu urbain. Une étude historique du mot calme a été réalisée à travers un corpus de dictionnaire du XVIe siècle à nos jours, pour mettre en évidence les différents sens rattachés à ce mot. Il est apparu que le lien vers le domaine sonore est tardif. De plus, la notion de calme est relative ce qui la différencie de la notion de tranquillité. Pour faire émerger les représentations actuelles, des ateliers de concertation ont été réalisés à Cergy-Pontoise et Paris. Ces deux approches ont permis de proposer des critères de caractérisation des zones calmes. Une enquête de portée nationale a ensuite été menée. Elle a permis de révéler 3 types de points de vue partagés par différents groupes de population. Pour certains, une zone calme est une zone de partage, pour d'autres une zone calme est un espace naturel et pour les derniers, une telle zone doit être silencieuse. La notion de contraste qui a émergé tout au long de ce travail a été étudiée plus en détails, à partir de test d'écoute en laboratoire et à partir des cartes de bruit. Un indicateur de contraste inspiré de la détection de contours en analyse d'image a été proposé. / Since 2002, European directive 2002/49/EC asks big cities to define quiet areas in order to protect them. The use of Lden indicator is suggested but member countries are free to suggest others. In order to help authorities in charge of directive application, this PhD work proposes a multidisciplinary approach to better define the quiet area notion in urban context. An historical study of the “calme” word was carried out through a dictionary corpus from the sixteenth century to nowadays to highlight the different meanings of this word. It appeared that the link to the sound field is late. Moreover, calm notion is relative what differs of tranquility concept. To highlight current representations, workshops with inhabitants were carried out in Cergy-Pontoise and Paris. These two approaches allow us to propose criteria to characterize quiet areas. Then, a national survey was conducted. It allowed to reveal 3 types of points of view shared by different groups of people. For some, a quiet area is a sharing zone, for others, a quiet area is a natural area and for the lasts, such area must be silent. The contrast notion that emerged throughout this work has been studied in more details, using listening tests in laboratory and, using noise maps. A contrast indicator inspired from edge detection in image analysis was proposed.

<p dir="ltr">Comprehensibility refers to the degree of effort that a listener requires to understand a speaker’s utterance (Derwing & Munro, 1997; Munro & Derwing, 1995; Derwing & Munro, 2005). Previous studies on L2 pronunciation have found that segmental errors could affect comprehensibility (Derwing et al., 1998; Derwing & Munro, 1997; Isaacs & Thomson, 2020; Saito et al., 2017). However, this finding only indicates a correlation between the number of segmental errors and lower comprehensibility. It is still unclear what aspects of pronunciation L2 learners need to practice in order to improve the comprehensibility of their speech. This thesis proposes that the degree of acoustic contrast may play a role in determining comprehensibility. More specifically, it investigates the relation between Mandarin speakers’ acoustic contrast between tense and lax vowels in English (i.e., [i] and [ɪ], [u] and [ʊ]) and the perceived comprehensibility of their speech.</p><p dir="ltr">A sentence production task and a comprehensibility rating task were conducted. In the sentence production task, 20 Mandarin speakers and 10 English speakers read aloud English sentences containing tense and lax vowels and were audio-recorded. The acoustic measurements of the vowels were taken in order to compare Mandarin speakers’ acoustic realization of the tense and lax vowels with English speakers’ productions. In the comprehensibility rating task, 48 English speakers transcribed the sentences recorded during the sentence production task and rated the comprehensibility of the sentences. The comprehensibility ratings were tested for correlation with the number of transcription errors, the degree of spectral and durational contrasts between vowels, and the speakers’ US residency length, in order to investigate the relation between intelligibility errors and comprehensibility, between acoustic contrast and comprehensibility, and between US residency length and comprehensibility.</p><p dir="ltr">The results of the linear-mixed effect model indicated that spectral contrast between [u] - [ʊ], but not [i] - [ɪ], was significantly reduced in Mandarin speakers’ productions compared to the English speakers, suggesting that Mandarin speakers under-differentiated the back vowel pair. A correlation test using Kendall’s <i>tau</i> indicated a significant negative correlation between number of intelligibility errors and comprehensibility, suggesting that intelligibility errors decreased comprehensibility. A correlation test using Kendall’s <i>tau</i> indicated a significant positive correlation between the degree of spectral contrast and comprehensibility rating for sentences with semantically meaningful context, suggesting that increasing the contrast between tense and lax vowels could help increase the comprehensibility of speech. Finally, a correlation test using Kendall’s <i>tau</i><i> </i>indicated no significant correlation between US residency length and comprehensibility, meaning that the relation between residency length and comprehensibility was not confirmed.</p><p dir="ltr">To sum up, acoustic contrast could be one of the contributors to speech comprehensibility. Therefore, directing English L2 learners to focus on increasing the acoustic distance between contrasting vowels could prove a fruitful strategy for improving the comprehensibility of L2 speech.</p>