The change a speaker makes in response to background noise is known as the Lombard Effect (LE). This study investigated the acoustic changes that are undergone in the presence of broadband noise and two-talker babble. Of particular interest were vocal fundamental frequency (F0) and formant frequency vowel space measures across sex. Forty participants (20 male, 20 female) were recruited and asked to read phrases in quiet and in the presence of two-talker babble and broadband noise. These masker conditions were presented at 50 and 70 dB HL. The phrases were recorded and acoustically analysed. The results showed a significant sex difference for both F0 and vowel space. A masking condition effect was not displayed for either F0 or vowel space. A significant effect was however shown for F0 according to intensity level, suggesting a LE. While the sex difference in F0 values can be explained on the basis of differences in vocal anatomy, the sex difference in vowel space was indicative of a sociophonetic influence on speech production.

The present study investigates the relevance of fundamental frequency in speech segmentation models intended to simulate infants. Speech from three different conditions (infant-directed speech to 3- and 12-month-olds, and adult-directed speech) was segmented based on fundamental frequency information, using a variant of the dpn-gram segmenting technique (highlighting similar segments as lexical candidates). The spectral distance between segments that were found based on fundamental frequency similarity was calculated, and compared to the spectral distance between segments that were found using transcription as basis for segmentation, as well as to the spectral distance between randomly paired segments from the same speech materials. The results show the greatest within-condition difference in speech directed to 3-month-olds, in which segmenting based on fundamental frequency similarity generated segment pairs with smaller spectral distance than did transcription-based segmentation or random segment pairs. Speech directed to 12-month-olds resulted in a somewhat smaller difference when using fundamental frequency data compared to when using transcriptions. For adult-directed speech, no difference was found in spectral distance between pairs generated by the different bases for segmentation. Neither segmenting speech by highlighting similar segments as lexical candidates, nor using fundamental frequency as basis for segmentation is optimal for a speech segmentation model intended to simulate 12-month-olds or adults. These groups are more likely to segment speech based on their already present or growing linguistic experience than on acoustic similarity only. However, for a model simulating a 3-month-old infant, the present segmentation procedure and its basis for segmentation are more plausible. When modeling speech segmentation in an infant-like manner it is important to take into account both that the cognitive abilities of infants develop rapidly during the first year of life, and that some aspects of their linguistic environment vary during this period.

The present Master's thesis deals with the forensic use of fundamental frequency characteristics, specifically with F0 mean values and indicators of variability. Phoneticians who specialise in the forensic analysis of speech generally believe that F0 does not hold much potential as a parameter useful for speaker identification, mainly because it is easily influenced by extrinsic factors (e.g. the speaker's emotional state, interfering noise, transmission channel or even the speaker's own effort to mask his voice), which cause high intra-individual variability. Despite these facts, however, the forensic use of F0 offers a number of advantages, namely straightforward extraction from the speech signal and lower susceptibility to varying lexical content - unlike, for example, vowel formants. This thesis investigates the recordings of 8 male speakers made in two different speech styles (spontaneous and read) and compares the respective indicators of F0 stability and variability, in particular those that are robust in varying external conditions: that is, the baseline for mean values and the 10.-90. percentile range for variability indicators. Apart from that, we take into account phenomena such as the creaky voice, which are idiosyncratic and contribute to easier speaker discrimination. Key words:...

Although the complexity of prosody is widely recognised, there is a lack of widely-accepted descriptive standards for prosodic phenomena. This situation has become particularly noticeable with the development of increasingly capable text-to-speech (TTS) systems. Such systems require detailed prosodic models to sound natural. For the languages of Southern Africa, the deficiencies in our modelling capabilities are acute. Little work of a quantitative nature has been published for the languages of the Nguni family (such as isiZulu and isiXhosa), and there are significant contradictions and imprecisions in the literature on this topic. We have therefore embarked on a programme aimed at understanding the relationship between linguistic and physical variables of a prosodic nature in this family of languages. We then use the information/knowledge gathered to build intonation models for isiZulu and isiXhosa as representatives of the Nguni languages. Firstly, we need to extract physical measurements from the voice recordings of the Nguni family of languages. A number of pitch tracking algorithms have been developed; however, to our knowledge, these algorithms have not been evaluated formally on a Nguni language. In order to decide on an appropriate algorithm for further analysis, evaluations have been performed on two stateof- the-art algorithms namely the Praat pitch tracker and Yin (developed by Alain de Cheveingn´e). Praat’s pitch tracker algorithm performs somewhat better than Yin in terms of gross and fine errors and we use this algorithm for the rest of our analysis.<./p> For South African languages the task of building an intonation model is complicated by the lack of intonation resources available. We describe the methodology used for developing a generalpurpose intonation corpus and the various methods implemented to extract relevant features such as fundamental frequency, intensity and duration from the spoken utterances of these languages. In order to understand how the ‘expected’ intonation relates to the actual measured characteristics extracted, we developed two different statistical approaches to build intonation models for isiZulu and isiXhosa. The first is based on straightforward statistical techniques and the second uses a classifier. Both intonation models built produce fairly good accuracy for our isiZulu and isiXhosa sets of data. The neural network classifier used produces slightly better results for both sets of data than the statistical method. The classification model is also more robust and can easily learn from the training data. We show that it is possible to build fairly good intonation models for these languages using different approaches, and that intensity and fundamental frequency are comparable in predictive value for the ascribed tone. / Dissertation (MSc (Computer Science))--University of Pretoria, 2006. / Computer Science / MSc / unrestricted

Cascaded H-bridge (CHB) multilevel inverters have significant popularity with motor drives applications due to their modularity, scalability, and reliability. Typical CHB inverters employ diode rectifiers that allow unidirectional power flow from the grid to the load. To capture and utilize the regenerated energy in regenerative applications, regenerative CHB drives were introduced with two-level voltage source converters in the front end to allow bidirectional energy flow. This solution is accompanied by challenges of high number of switches and control circuits, high switching power losses, and massive dimensions. Recently, developing more economic versions of regenerative cascaded H-bridge drives has become one of the hottest topics in power electronics research. In this thesis work, two solutions are proposed for more energy efficient and economic regenerative CHB drives. The first solution is a proposed power cell configuration that reduces the number of switches per cell by two. Additionally, phase alternation connection method and carrier phase-shifting techniques are introduced to address the challenges of the presented configuration. The switch-count reduction reduces the system’s complexity, switches’ cost, and footprint. The second proposed solution is a new controller to operate the front-end converters as fundamental frequency ends (FFEs). The proposed controller is employed in both the conventional regenerative cascaded H-bridge and the proposed reduced switch-count configuration. This solution minimizes the switching power losses, and results in more compact and economic design, with higher DC-link utilization. Theoretical analysis and simulation studies of both proposed solutions show promising performance and capability to be applied as energy-efficient and cost effective regenerative CHB motor drives. Experimental validation of the proposed reduced switch-count configuration is presented for STATCOM operation of a scaled-down 7-Level regenerative CHB drive system. The future work of this thesis includes experimental validation of the proposed FFE controller, and operation of the system with regenerative motor load. / Thesis / Master of Applied Science (MASc)

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<p>Previous research indicates that vocal and facial masculinity and femininity influence perceptions of attractiveness. Men generally perceive women with feminine traits as more attractive than less feminine women. This may be because women who possess more feminine traits are likely to be healthier and more fertile mates than are less feminine women. Masculine male traits also influence women’s perceptions of attractiveness. Although women do not always prefer masculine male traits, preferences for masculinity are observed under circumstances where women may gain the fitness benefits of heritable health and dominance. Masculine traits in men and feminine traits in women are further associated with the potential fitness risks of infidelity and reduced investment in mates. Here I address three previously unanswered questions concerning the influence of masculinity and femininity on social perceptions. First, how do male vocal and facial masculinity influence perceptions of attractiveness when these two traits are presented simultaneously? Second, does vocal masculinity influence perceptions of the potential fitness risks of infidelity and reduced relationship investment in mates? Third, do male masculinity and female femininity influence perceptions of potential same-sex rivals? In this dissertation I demonstrate that simultaneously presented male vocal and facial masculinity influence women’s perceptions of men’s attractiveness, that perceivers are somewhat aware of the potential fitness risks associated with preferring high quality mates, and that vocal and facial masculinity influence mate choice and intrasexual competition in similar ways. Overall, these studies demonstrate the pervasive influence of masculinity and femininity on mate-choice relevant social perceptions.</p> / Doctor of Philosophy (PhD)