Thesis (DPhil)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The area of study is the notion of validity in image-based research, i.e. research approaches where visual images such as photographs or video recordings form an integral part of one or more of the methods used. In the literature investigation chapters of the study, (1) the notion of validity is reviewed with special reference to contributions by Cook and Campbell, Guba and Lincoln, Kvale, Lather and Morse; (2) the inherent properties of visual images are discussed from a semiotic perspective, and (3) following a discussion of reflexivity in image-based research, the various domains of image-based research practice are demarcated according to the unit of analysis, the data format, the researcher role (outsider, insider, participant) and the production of the visual material (ex ante or ex post with weak or strong researcher control). The literature investigation chapters were taken as the point of departure for the development of a conceptual framework for assessing validity in image-based research, the mechanics of which are illustrated with reference to selected aspects of image-based research projects by Lomax and Casey, Clark and Zimmer, Rich and Chalfen, DuFon and Chaplin. The conceptual framework was refined on the strength of a Delphi study. The Delphi procedure involved canvassing and pooling the opinions of experts in the field of image-based research about issues of validity with a view to ensure that the assumptions made during the development of the conceptual framework fit sufficiently with image-based research practice. Flowing from the literature investigation chapters as well as the Delphi procedure, the central thesis of the study is that the notion of validity is in the first instance contextdependent and that this is compounded in the case of image-based research by the relative instability of iconic codes and the strong drift towards 'unlimited' semiosis inherent in the visual communication process. / AFRIKAANSE OPSOMMING: Die studieveld behels ‘n ondersoek na die gedagte van geldigheid soos van toepassing op beeldgebaseerde navorsing, d.w.s. navorsingsbenaderings waar visuele beelde soos foto’s of video-opnames ‘n integrale deel uitmaak maak een of meer van die metodes wat gebruik word. In die hoofstukke wat die literatuurstudie uitmaak, word (1) die gedagte van geldigheid onder die loep geneem met spesifieke verwysing na die bydraes van Cook en Campbell, Guba en Lincoln, Kvale, Lather en Morse, (2) word die inherente eienskappe van visuele beelde vanaf 'n semiotiese oogpunt bespreek, en (3) word die verskeie velde van beeldgebaseerde navorsingspraktyk afgebaken volgens die eenheid van ontleding, die dataformaat, die rol van die navorser (buitestaander, binnestaander, deelnemer) en die produksie van die visuele materiaal (ex ante of ex post met sterk of swak navorserkontrole). Die hoofstukke wat gemoeid is met die literatuurstudie is as vertrekpunt geneem vir die daarstelling van ‘n konsepsuele raamwerk vir geldigheid aangaande beeldgebaseerde navorsing, en die werking hiervan is geïllustreer met verwysing na geselekteerde aspekte van beeldgebaseerde navorsing deur Lomax en Casey, Clark en Zimmer, Rich en Chalfen, DuFon end Chaplin. Hierdie konsepsuele raamwerk is verder verfyn op grond van ‘n Delphi-prosedure. Die Delphi-prosedure het behels dat die opinies van deskundiges in die veld van beeldgebaseerde navorsing aangaande kwessies van geldigheid ingewin en saamgevoeg is met die oog om te verseker dat die aannames wat gemaak is ten tyde van die ontwikkeling van die konsepsuele raamwerk genoegsaam gepas is vir die praktyk van beeldgebaseerde navorsing. Die tesis van die studie, gebaseer op die uitkomste van die literatuurstudie en die Delphi-prosedure, is dat die gedagte van geldigheid konteks-afhanklik is, wat in die geval van beeldgebaseerde navorsing vererger word deur die feit dat ikoniese kodes relatiefonstabiel is en dat die proses van visuele kommunikasie 'n sterk tendens na 'eindelose' semiosis toon.

Thesis (DPhil)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: South African society presents a complex and diverse environment to social scientists. Within immense economic stratification; a multitude of cultures and classes; languages and their dialects; and varied racial groups, researchers attempt to produce information that contributes constructively to policy, programs and a host of services. Beneath the surface also lay complex power issues informed by both political and cultural histories. Many contexts in which researchers find themselves continue to be marginalised and oppressed due to factors such as illiteracy and low-levels of education, age, gender and poverty. These groups often include women and children, in particular adolescents. Qualitative visual methods may provide researchers with a tool by which to address many of the concerns raised in the literature surrounding research carried out under such conditions. Visual methods may remove inherent power imbalances, as well as traditional barriers, such as culture and language, that stem from more 'conservative' research methods. Images may allow participants to vocalise the taken-for-granted in their lives in an empowering manner. The recognition and use of visual images in research with marginalised and oppressed groups is being increasingly recognised by the larger research community. A preliminary overview of the available literature highlights existing disagreement surrounding the theoretical underpinnings of visual methods. This is particularly seen in the various and confusing levels of abstraction presented in the literature. The primary aim of this study is therefore, to gain clarity and understanding as regards the methodological and epistemological underpinnings of visual research methods within the social sciences. As such, a comprehensive literature review has been conducted. A second aim of the study is to set out a typology of methods that would be relevant for use in marginalised communities. The third aim of the study is empirical in nature and aims to highlight the role and/or possibilities of visual research methods within the South African social sciences research context. This is achieved by means of a case study which explores how motherhood is experienced by five teenagers in a sub-economic community outside of Cape Town. It does this by providing participants cameras with which to visually express their understanding and experiences of motherhood. Processed photographs in this case study have been analysed by means of informal discussion, directed by the images, with the participants themselves. These discussions were recorded and transcribed. The results of the interviews were then analysed using grounded theory (Glaser & Strauss, 1967). The results emerging from this have been compared with relevant literature. In this way, results are also triangulated, adding to their reliability (Lucchinni, 1996). Consequently, results of this case study provide a comparative component by which to assess the applicability of visual methods in the South African research context. Both the literature review as well as experiences of the case study also form the basis of suggestions for further exploration. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse gemeenskap bied 'n komplekse en diverse omgewing aan sosiale wetenskaplikes. Binne hewige ekonomiese stratifikasie; 'n verskeidenheid kulture en klasse; tale en dialekte en diverse rassegroepe, poog navorsers om inligting te verskaf om 'n konstruktiewe bydrae te maak aan riglyne, programme en 'n legio dienste. Onder die oppervlakte lê daar ook komplekse magstryde afkomstig van beide 'n kuitereie en politieke geskiedenis. Vele omstandighede waarin navorsers hulself vind word steeds oorheers deur marginalisasie en onderdrukking as gevolg van faktore soos ongeletterdheid, lae vlakke van opvoeding, ouderdom, geslag en armoede. Hierdie groepe bestaan dikwels uit, onder andere, vroue en kinders. Kwalitatiewe visuele tegnieke mag navorsers van die nodige metodes voorsien waarmee verskeie probleme wat in die literatuur uitgelig word aangaande hierdie navorsing, aangespreek kan word. Visuele tegnieke mag inherente magsongelykhede, sowel as tradisionele struikelblokke, soos kultuur en taal wat afkomstig is uit meer 'konserwatiewe' navorsingstegnieke, verwyder. Uitbeeldings mag deelnemers toelaat om die vanselfsprekende in hullewens in 'n opbouende wyse te vokaliseer. Die identifisering en gebruik van visuele uitbeeldings in navorsing met gemarganaliseerde en onderdrukte groepe word tot 'n toenemende mate erken deur die uitgebreide navorsingsgemeenskap. 'n Voorlopige oorsig van die beskikbare literatuur beklemtoon bestaande onenigheid met betrekking tot die teoretiese fondamente van visuele tegnieke. Dit is veral duidelik sigbaar in die uitgebreide en verwarde vlakke van abstraktheid wat in die literatuur voorgestel word. Die primêre doelwit van hierdie studie is dus om groter helderheid en insig met betrekking tot die metodologiese en epistemologiese grondbeginsels van visuele metodes, soos dit in die sosiale wetenskappe voorkom, te verkry. Met hierdie doel voor oë is 'n uitgebreide literatuurondersoek onderneem. 'n Tweede doel van die studie is om 'n tipologie van metodes uiteen te sit wat relevant kan wees in gemarginaliseerde gemeenskappe. 'n Derde doel van die studie is empiries van aard en beoog om die rol en/of moontlikhede van visuele tegnieke binne die Suid-Afrikaanse sosiale wetenskaplike navorsings konteks te beklemtoon. Dit word bereik deur middel van 'n studie wat ondersoek hoe moederskap ondervind word deur vyf tieners in 'n sub-ekonomiese gemeenskap in die buitewyke van Kaapstad. Dit word uitgevoer deur deelnemers te voorsien van kameras waarmee hul begrip en ondervindings van moederskap visueel uitbeeld. 'n Verdere analise van hierdie studie is deur middel van informele besprekings uitgevoer met die deelnemers, begelei deur die uitbeeldings. Sodanige besprekings is opgeneem en getranskribeer. Die resultate verkry vanuit die onderhoude is daarna geanaliseer deur middel van begronde teorie (Glaser & Strauss, 1967). Die resultate wat hieruit afkomstig was, is vergelyk met relevante literatuur. Op hierdie wyse is resultate bevestig, wat ook verder tot hul betroubaarheid gespreek het (Lucchinni, 1996). Die gevolg is dat die resultate van hierdie studie 'n vergelykende komponent verskaf waarmee die toepaslikheid van visuele tegnieke in die Suid-Afrikaanse navorsingskonteks gemeet kan word. Beide die literatuurstudie, asook die ondervindings vanuit die gevallestudie vorm die basis vir aanbevelings vir verdere ondersoek.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / Digital audio data storage mediums have long been used within the consumer market. Today, because of the advancement of processor clock speeds and increased MOSFET switching capabilities, digital audio data formats can be directly amplified using power electronic inverters. These amplifiers known as Class-D have an advantage over there analogue counterparts because of their high efficiency. This thesis deals with the signal processing algorithms necessary to convert the digital audio data obtained from the source to a digital pulse width modulated signal which controls a full bridge inverter for audio amplification. These algorithms address difficulties experienced in the past which prevented high fidelity digital pulse width modulators to be implemented. The signal processing algorithms are divided into modular blocks, each of which are defined in theory, designed and simulated in Matlab® and then implemented within VHDL firmware. These firmware blocks are then used to realize a Class-D audio amplifier.

Thesis (MScEng)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: The class-D audio power amplifier has found widespread use in both the consumer and professional audio industry for one reason: efficiency. A higher efficiency leads to a smaller and cheaper design, and in the case of mobile devices, a longer battery life. Unfortunately, the basic class-D amplifier has some serious drawbacks. These include high distortion levels, a load dependent frequency response and the potential to radiate EMI. Except for EMI, the aforementioned issues can be mitigated by the proper implementation of global negative feedback. Negative feedback also has the potential to indirectly reduce EMI, since the timing requirements of the output devices can be relaxed. This thesis discusses the design of a clocked analogue controlled pulse-width modulated class-D audio amplifier with global negative feedback. The analogue control loop is converted to the z-domain by modelling the PWM comparator as a sampling operation. A method is implemented that improves clip recovery and ensures stability during over-modulation. Loop gain is shaped to provide a high gain across the audio band, and ripple compensation is implemented to minimize the negative effect of ripple feedback. Experimental results are presented. / AFRIKAANSE OPSOMMING: Die klas-D klankversterker geniet wydverspreide gebruik in beide die verbruiker en professionele oudio industrie vir een rede: benuttingsgraad. ’n Hoër benuttingsgraad lei tot ’n kleiner en goedkoper ontwerp, en in die geval van draagbare toestelle, tot langer batterylewe. Ongelukkig het die basiese klas-D klankversterker ernstige tekortkominge, naamlik hoë distorsievlakke, ’n lasafhanklike frekwensierespons en die vermoë om EMI te genereer. Behalwe vir EMI kan hierdie kwessies deur die korrekte toepassing van globale negatiewe terugvoer aangespreek word. Negatiewe terugvoer het ook die potensiaal om EMI indirek te verminder, aangesien die tydvereistes van die skakel stadium verlaag kan word. Hierdie tesis bespreek die ontwerp van ’n geklokte analoog-beheerde pulswydte-modulerende klas-D klankversterker met globale negatiewe terugvoer. Die analoogbeheerlus word omgeskakel na die z-vlak deur die PWM vlakvergelyker as ’n monster operasie te modelleer. ’n Metode word geïmplementeer wat die stabiliteit van die lus verseker tydens oormodulasie. Die lusaanwins word gevorm om ’n hoë aanwins in die oudioband te verseker en riffelkompensasie word geïmplementeer om die negatiewe effek van terugvoerriffel teen te werk. Eksperimentele resultate word voorgelê.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / The aim of this thesis is to implement a Digital Audio Broadcasting (DAB) system in a Software Defined Radio (SDR). The physical modulation part of the DAB transmitter for one of the transmission modes as well as its receiver is to be implemented and tested in the SDR. DAB transmission mode II is implemented.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Telephony has developed substantially over the years, but the fundamental auditory model of mixing all the audio from di erent sources together into a single monaural stream has not changed since the telephone was rst invented. Monaural audio is very di cult to follow in a multiple-source situation such as a conference call. Sound originating from a speci c point in space will travel along a slightly di erent path to each ear. Although we are not consciously aware of it, our brain processes these spatial cues to help us to locate sounds in space. It is this spatial information that allows us to focus our attention and listen to a single speaker in an environment where many di erent sources may be active at the same time; a phenomenon known as the \cocktail party e ect". It is possible to reproduce these spatial cues in a sound recording, using Head-Related Transfer Functions (HRTFs) to allow a listener to experience localised audio, even when sound is reproduced through a headset. In this thesis, spatial audio is implemented in a telephony application as well as in a virtual world. Experiments were conducted which demonstrated that spatial audio increases the intelligibility of speech in a multiple-source environment and aids active speaker identi cation. Resource usage measurements show that these bene ts are, however, not without a cost. In conclusion, spatial audio was shown to be an improvement over the monaural audio model traditionally implemented in telephony. / AFRIKAANSE OPSOMMING: Telefonie het ansienlik ontwikkel oor die jare, maar die basiese ouditiewe model waarin die klank van alle verskillende bronne bymekaar gemeng word na een enkelouditoriese stroom het nie verander sedert die eerste telefoon gebou is nie. Enkelouditoriese klank is baie moeilik om te volg in 'n meervoudigebron situasie, soos byvoorbeeld in 'n konferensie oproep. Klank met oorsprong by 'n sekere punt in die ruimte sal 'n e ens anderse pad na elke oor volg. Selfs is ons nie aktief bewus hiervan nie, verwerk ons brein hierdie ruimtelike aanduidinge om ons te help om klanke in die ruimte te vind. Dit is hierdie ruimtelike inligting wat ons toelaat om ons aandag te vestig en te luister na 'n enkele spreker in 'n omgewing waar baie verskillende bronne terselfdertyd aktief mag wees, 'n verskynsel wat bekend staan as die \skemerkelkiepartytjiee ek". Dit is moontlik om hierdie ruimtelike leidrade na 'n klank te reproduseer met behulp van hoofverwandeoordragfunksies (HRTFs) en om daardeur 'n luisteraar gelokaliseerde klank te laat ervaar, selfs wanneer die klank deur middel van oorfone gespeel word. In hierdie tesis word ruimtelike klank ge mplementeer in 'n telefonieprogram, sowel as in 'n virtuelew^ereld. Eksperimente is uitgevoer wat getoon het dat ruimtelike klank die verstaanbaarheid van spraak in 'n meerderebronomgewing verhoog en help met aktiewe spreker identi kasie. Hulpbrongebruiks metings toon aan dat hierdie voordele egter nie sonder 'n koste kom nie. Ter afsluiting, dit is bewys dat ruimtelike klank 'n verbetering tewees gebring het oor die enkelouditorieseklankmodel wat tradisioneel in telefonie gebruik het.

Use of mobile equipment has increased exponentially over the last decade. As use becomes more widespread so too does the demand for new functionalities. The limited memory and computational power of many mobile devices has proven to be a challenge resulting in many innovative solutions and a number of new standards. Despite this, there is often a requirement for additional enhancement to improve quality. The focus of this thesis work has been to perform enhancement within two different areas; audio or speech encoding and video encoding/decoding. The audio enhancement section of this thesis addresses the well known problem in the GSM system with an interfering signal generated by the switching nature of TDMA cellular telephony. Two different solutions are given to suppress such interference internally in the mobile handset. The first method involves the use of subtractive noise cancellation employing correlators, the second uses a structure of IIR noth filters. Both solutions use control algorithms based on the state of the communication between the mobile handset and the base station. The video section of this thesis presents two post-filters and one pre-filter. The two post-filters are designed to improve visual quality of highly compressed video streams from standard, block-based video codecs by combating both blocking and ringing artifacts. The second post-filter also performs sharpening. The pre-filter is designed to increase the coding efficiency of a standard block based video codec. By introducing a pre-processing algorithm before the encoder, the amount of camera disturbance and the complexity of the sequence can be decreased, thereby increasing coding efficiency.

The complex relationship between array gain patterns and microphone distributions limits the application of traditional optimization algorithms on irregular arrays, which show enhanced beamforming performance for human speech capture in immersive environments. This work analyzes the relationship between irregular microphone geometries and spatial filtering performance with statistical methods. Novel geometry descriptors are developed to capture the properties of irregular microphone distributions showing their impact on array performance. General guidelines and optimization methods for regular and irregular array design are proposed in immersive (near-field) environments to obtain superior beamforming ability for speech applications. Optimization times are greatly reduced through the objective function rules using performance-based geometric descriptions of microphone distributions that circumvent direct array gain computations over the space of interest. In addition, probabilistic descriptions of acoustic scenes are introduced to incorporate various levels of prior knowledge for the source distribution. To verify the effectiveness of the proposed optimization methods, simulated gain patterns and real SNR results of the optimized arrays are compared to corresponding traditional regular arrays and arrays obtained from direct exhaustive searching methods. Results show large SNR enhancements for the optimized arrays over arbitrary randomly generated arrays and regular arrays, especially at low microphone densities. The rapid convergence and acceptable processing times observed during the experiments establish the feasibility of proposed optimization methods for array geometry design in immersive environments where rapid deployment is required with limited knowledge of the acoustic scene, such as in mobile platforms and audio surveillance applications.

Ce document est organisé en quatre chapitres dont trois rédigés en anglais et une annexe en français. Le premier chapitre décrit mes contributions dans le domaine de la séparation de sources audio, qui constituent certainement le volet le plus appliqué de mon activité scientifique, volet auquel ont contribué significativement plusieurs doctorants et collaborateurs. Les deux chapitres suivants sont consacrés aux aspects plus mathématiques de mon travail, le premier sur les approximations non-linéaires avec des dictionnaires redondants, en collaboration étroite avec Morten Nielsen, le second sur l'analyse des performances des algorithmes de décomposition parcimonieuse, avec le concours notamment de Pierre Vandergheynst. Dans ces trois chapitres, j'ai adopté un style sans doute peu conventionnel dans la littérature scientifique : j'y ai opté pour le "je" plus que le "nous" et j'ai choisi d'agrémenter le texte de divers éléments de contexte. L'annexe, dans un style plus traditionnel, reproduit le chapitre de synthèse « Séparation de sources basée sur la parcimonie » que j'ai écrit pour l'ouvrage « Séparation de Sources » coordonné par Pierre Comon et Christian Jutten dans la collection IC2 publié par Hermès.

<p>In printed text, sound is a somewhat forgotten aspect. The recitation of text is vital in areas like poetry and oratory, but still has no distinct technique of being communicated. Emphasis of a word might be expressed through italics, but no canonic character set or system for vocal delivery of texts exists. With this essay we are creating a foundation for a development of such a character set or system. By studying existing visualisations of sound and comparing these with semiotic and perception-based theories we obtain useful insights for a prospective system for visualisations of vocal sounds.</p><p>We conclude that the aspects of sound one wants to visualise must be carefully defined since the viewer cannot process infinite amounts of information. A sound visualisation system does not have to consist of multiple characters or signs to be effective, but had better be built around a strong code to manage the signs into a working system. Creating a context for the signs is also recommended in order to be able to compare signs with eachother.</p>