When considering the acoustics of a room as a linear time-invariant system, the room impulse response (RIR) describes the response of the room to an audio signal from a given source position to a given receiver position. If the RIR is perfectly known, the response of the room to any acoustic signal can be predicted. In practice, however, there are several difficulties. For a reverberant room, a finite impulse response (FIR) representation of the RIR can be on the order of 100 000 samples. Considering the position dependence of the RIR, the complete description of a room requires the RIRs for a multitude of closely spaced source and receiver positions. This is problematic from both a storage and a processing point of view, as the convolution with long FIR filters, e.g., for the purpose of auralization, is computationally demanding, particularly ...

This thesis is related to the field of Sound Source Separation (SSS). It addresses the development and evaluation of these techniques for their application in the resynthesis of high-realism sound scenes by means of Wave Field Synthesis (WFS). Because the vast majority of audio recordings are preserved in two-channel stereo format, special up-converters are required to use advanced spatial audio reproduction formats, such as WFS. This is due to the fact that WFS needs the original source signals to be available, in order to accurately synthesize the acoustic field inside an extended listening area. Thus, an object-based mixing is required. Source separation problems in digital signal processing are those in which several signals have been mixed together and the objective is to find out what the original signals were. Therefore, SSS algorithms can be applied to existing two-channel mixtures to ...

The central topic of this thesis is Reverberation. Reverberation is used as a global term to describe a series of physical and perceptual phenomena that occur in enclosed environments and relate to the acoustical interaction between a sound source and the enclosure. This work focuses on the effects of reverberation that are likely to occur within common listening environments, such as car cabins and ordinary residential listening rooms. In the first study, a number of acoustical fields was captured in a physically modified car cabin and evaluated by expert listeners in a laboratory, using a spatial reproduction system. In the second study, nine acoustical conditions from four ordinary listening rooms were perceptually evaluated by experienced listeners. The results indicated the importance of decay times in these types of enclosures, even in these theoretically short and nondominant quantities. It was shown ...

The ability of humans to perceive sound spatially is based on binaural hearing, i.e. on signals arriving at the two ears which supply the listener with important spatial and spectral cues. The aim of binaural technology is to capture and reproduce the sound field in such a way that these cues are preserved. A well-known drawback of using artificial heads for this aim is that they exhibit different anthropometrical measures compared to individual listeners. When playing back the recorded signals over headphones, the non-individual design of artificial heads may lead to localization ambiguities such as front-back reversals and perception inside the head. Moreover, it is hardly possible to achieve dynamic signal playback, accounting for the listener's head movements. As an alternative, it has been proposed to use a Virtual Artificial Head (VAH), which is a microphone array where spectral weights ...

Within the context of long-term access to digital objects in general this dissertation takes the longevity of digital surrogates of historical photographs into consideration. For memory institutes digitisation of analogue source material, such as historical photographs, is an exciting way to open up and exploit their holdings. The focus on the digital durability of this specific type of digital object enables the investigation of available building blocks for digital preservation, such as strategies, guidelines, standards, procedures and tools. A benchmarked digital capture process, the unambiguous formulation of preservation metadata and the application of persistent identifiers for digital objects, all based on open standards are important building blocks for the realisation of durable digital surrogates of historical photographs. Three methods for creating durable digital objects are assessed in detail. These are the application of a standardised digital image file format, the ...

In today's audio production and reproduction as well as in music performance practices it has become common practice to alter reverberation artificially through electronics or electro-acoustics. For music productions, radio plays, and movie soundtracks, the sound is often captured in small studio spaces with little to no reverberation to save real estate and to ensure a controlled environment such that the artistically intended spatial impression can be added during post-production. Spatial sound reproduction systems require flexible adjustment of artificial reverberation to the diffuse sound portion to help the reconstruction of the spatial impression. Many modern performance spaces are multi-purpose, and the reverberation needs to be adjustable to the desired performance style. Employing electro-acoustic feedback, also known as Reverberation Enhancement Systems (RESs), it is possible to extend the physical to the desired reverberation. These examples demonstrate a wide range of applications ...

Personal Sound Zones (PSZ) systems deliver different sounds to a number of listeners sharing an acoustic space through the use of loudspeakers together with signal processing techniques. These systems have attracted a lot of attention in recent years because of the wide range of applications that would benefit from the generation of individual listening zones, e.g., domestic or automotive audio applications. A key aspect of PSZ systems, at least for low and mid frequencies, is the optimization of the filters used to process the sound signals. Different algorithms have been proposed in the literature for computing those filters, each exhibiting some advantages and disadvantages. In this work, the state-of-the-art algorithms for PSZ systems are reviewed, and their performance in a reverberant environment is evaluated. Aspects such as the acoustic isolation between zones, the reproduction error, the energy of the filters, ...

Recently emerging techniques like wave field synthesis (WFS) or Higher-Order Ambisonics (HOA) allow for high-quality spatial audio reproduction, which makes them candidates for the audio reproduction in future telepresence systems or interactive gaming environments with acoustic human-machine interfaces. In such scenarios, acoustic echo cancellation (AEC) will generally be necessary to remove the loudspeaker echoes in the recorded microphone signals before further processing. Moreover, the reproduction quality of WFS or HOA can be improved by adaptive pre-equalization of the loudspeaker signals, as facilitated by listening room equalization (LRE). However, AEC and LRE require adaptive filters, where the large number of reproduction channels of WFS and HOA imply major computational and algorithmic challenges for the implementation of adaptive filters. A technique called wave-domain adaptive filtering (WDAF) promises to master these challenges. However, known literature is still far away from providing sufficient insight ...

This work deals with the advancement of wideband hands-free systems (HFS’s) for mono- and stereophonic cases of application. Furthermore, innovative contributions to the corr. field of quality evaluation are made. The proposed HFS approaches are based on frequency-domain adaptive filtering for system identification, making use of Kalman theory and state-space modeling. Functional enhancement modules are developed in this work, which improve one or more of key quality aspects, aiming at not to harm others. In so doing, these modules can be combined in a flexible way, dependent on the needs at hand. The enhanced monophonic HFS is evaluated according to automotive ITU-T recommendations, to prove its customized efficacy. Furthermore, a novel methodology and techn. framework are introduced in this work to improve the prototyping and evaluation process of automotive HF and in-car-communication (ICC) systems. The monophonic HFS in several configurations ...

The term extended reality refers to all possible interactions between real and virtual (computed generated) elements and environments. The extended reality field is rapidly growing, primarily through augmented and virtual reality applications. The former allows users to bring digital elements into the real world, while the latter lets us experience and interact with an entirely virtual environment. While currently extended reality implementations primarily focus on the visual domain, we cannot underestimate the impact of auditory perception in order to provide a fully immersive experience. As a matter of fact, effective handling of the acoustic content is able to enrich the engagement of users. We refer to Extended Audio Reality (EAR) as the subset of extended reality operations related to the audio domain. In this thesis, we propose a parametric approach to EAR conceived in order to provide an effective and ...

Modern devices such as mobile phones, tablets or smart speakers are commonly equipped with several loudspeakers and microphones. If, for instance, one employs such a device for hands-free communication applications, the signals that are reproduced by the loudspeakers are propagated through the room and are inevitably acquired by the microphones. If no processing is applied, the participants in the far-end room receive delayed reverberated replicas of their own voice, which strongly degrades both speech intelligibility and user comfort. In order to prevent that so-called acoustic echoes are transmitted back to the far-end room, acoustic echo cancelers are commonly employed. The latter make use of adaptive filtering techniques to identify the propagation paths between loudspeakers and microphones. The estimated propagation paths are then employed to compute acoustic echo estimates, which are finally subtracted from the signals acquired by the microphones. In ...

Historical photos are significant attestations of the inheritance of the past. Since Photography is an art that is more than 150 years old, more and more diffuse are the photographic archives all over the world. Nevertheless, time and bad preservation corrupts physical supports, and many important historical documents risk to be ruined and their content lost. Therefore solutions must be implemented to preserve their state and to recover damaged information. This PhD thesis proposes a general methodology, and several applicative solutions, to handle these problems, by means of digitization and digital restoration. The purpose is to create a useful tool to support non-expert users in the restoration process of damaged historical images. The content of this thesis is outlined as follows: Chapter 1 gives an overview on the problems related to management and preservation of cultural repositories, and discusses about ...

Binaural technology aims to reproduce three-dimensional auditory scenes with a high level of realism by providing the auditory display with spatial hearing information. This technology has various applications in virtual acoustics, architectural acoustics, telecommunication and auditory science. One key element in binaural technology is the actual binaural signals, produced by filtering a sound-field with free-field head related transfer functions (HRTFs). With the increased popularity of spherical microphone arrays for sound-field recording, methods have been developed for rendering binaural signals from these recordings. The use of spherical arrays naturally leads to processing methods that are formulated in the spherical harmonics (SH) domain. For accurate SH representation, high-order functions, of both the sound-field and the HRTF, are required. However, a limited number of microphones, on one hand, and challenges in acquiring high resolution individual HRTFs, on the other hand, impose limitations on ...

Due to their decreased ability to understand speech hearing impaired may have difficulties to interact in social groups, especially when several people are talking simultaneously. Fortunately, in the last decades hearing aids have evolved from simple sound amplifiers to modern digital devices with complex functionalities including noise reduction algorithms, which are crucial to improve speech understanding in background noise for hearing-impaired persons. Since many hearing aid users are fitted with two hearing aids, so-called binaural hearing aids have been developed, which exchange data and signals through a wireless link such that the processing in both hearing aids can be synchronized. In addition to reducing noise and limiting speech distortion, another important objective of noise reduction algorithms in binaural hearing aids is the preservation of the listener’s impression of the acoustical scene, in order to exploit the binaural hearing advantage and ...

This thesis addresses the development and enhancement of Multiactuator Panels (MAPs) with emphasis on the application to Wave Field Synthesis (WFS) reproduction. MAPs can be used alternatively to dynamic loudspeaker arrays for WFS with added benefits. However, since MAPs are panels of finite extent, excited mechanically on several points, there are structural and geometric issues that must be addressed to guarantee that all exciters are acting evenly to form an effective loudspeaker array for WFS. This aim is addressed by means of a methodology for the analysis of sound field radiation in the space-time domain that has been proposed and validated in this thesis. This research has produced a number of key conclusions. The proposed method analyzes aliasing artifacts in a graphical representation showing the distribution of radiated energy over space. In a comparative study between MAPs of different dimensions ...