Residual feedback suppression with extended model-based postfilters

When designing closed-loop electro-acoustic systems, which can commonly be found in hearing aids or public address systems, the most challenging task is canceling and/or suppressing the feedback caused by the acoustic coupling of the transducers of such systems. In many applications, feedback cancelation based on adaptive filters is used for this purpose. However, due to computational complexity such a feedback canceler is often limited in the length of the filter’s impulse response. Consequently, a residual feedback, which is still audible and may lead to system instability, remains in most cases. In this work, we present enhancements for model-based postfilters based on a priori knowledge of the feedback path which can be used cooperatively with the adaptive filter-based feedback cancelation system to suppress residual feedback and improve the overall feedback reduction capability. For this, we adapted an existing reverberation model such that our model additionally considers the presence and the performance of the adaptive filter. We tested the effectiveness of our approach by means of both objective and subjective evaluations

Enhancement of degraded speech by removing dissonant components

Tato práce se zabývá metodou pro částečné odstranění rušivých vlivů z řečového signálu, čímž dochází k celkovému zlepšení kvality znehodnoceného řečového signálu a zlepšení SRN. Konkrétně se jedná o odstranění nejčastějších typů rušení, která skutečně ovlivňují srozumitelnost a kvalitu aplikací pro úlohu zpracování řečového signálu. Jsou to přeslechy z ostatních okolních rozhovorů, hluk automobilu, hluk ventilátoru počítače, hluk větru přicházejícího na mikrofon a obecný šum. Níže popsaná metoda, je založena na filtrování frekvenčních pásem, která se zobrazují jako tóny disharmonických intervalů. Velikost intervalu jednotlivých disharmonických jevů je vztahována k základnímu tónu řeči, který si lze představit v oblasti temperovaného ladění jako tón C, čímž se disharmonické složky spektra řečového signálu zobrazují jako tóny F#, B a C#. Cílem práce je navržení funkční metody a vlastního technického řešení pro realizaci v prostředí Matlab. Odstranění co největšího podílu rušivých složek ve znehodnoceném signálu metodou hřebenové filtrace disharmonických složek v šířce osmi slyšitelných oktáv.This work deals with the method of partial removal of interference from the speech signal, thereby improving the overall quality of depreciated speech signal and improve signal-to-noise ratio. Specifically, the elimination of frequent disturbance, such as crosstalk from other interviews, noise, car noise, computer fans wind coming to the microphone and general noise. The method described below is based on frequency filtering, which can be thought of as the discordant tones of intervals. The size range of discordant phenomena, be applied to the basic tone of speech, which can be thought of as a tone tempered tuning C, and thus a spectrum of dissonant speech appear as notes F #, B, and C #. The aim of my work is finding its own working methods and technical solutions for realization of removing the greatest proportion of interfering components in the signal deteriorated by filtration discordant elements.

Instrumentelle Evaluierung von Innenraum-Kommunikationssystemen

Die Kommunikation zwischen den Insassen eines schnell fahrenden Fahrzeuges kann stark beeinträchtigt sein. Insbesondere die Gespräche zwischen den vorderen Passagieren und denen der Rücksitzbank sind, aufgrund der Geräuschkulisse und der Anordnung, erschwert. Für gewöhnlich verändern die Insassen ihre Position und ihre Sprache, um diese Beeinträchtigung zu kompensieren. Eine weitere Methode die Kommunikationssituation zu verbessern, ist ein sogenanntes ICC-System. Solche Systeme nehmen das Sprachsignal einer Person mithilfe von Mikrofonen auf, verarbeiten dieses und geben das verstärkte Nutzsignal in der Fahrgastzelle, nahe dem Zuhörer wieder aus. Dadurch erhöht sich die Nutzsignalleistung im Fahrzeug und die Verständlichkeit. Nach der erfolgreichen Umsetzung und Entwicklung solcher Systeme stellt sich die Frage nach der Qualität des ICC-Systems. Zur Beantwortung dieser Frage wird in dieser Arbeit zunächst der Begriff Qualität im Sinne eines ICC-Systems eingeordnet. Anschließend wird eine Evaluierungsstrategie, welche aus einer Vielzahl an einzelnen, instrumentellen Verfahren besteht, vorgestellt. Für eine eingängige Klassifizierung der Verfahren und eine transparente Erhebung einer Gesamtqualität, werden diese in drei verschiedene Evaluierungsgruppen unterteilt. Es handelt sich hierbei um Verfahren, welche die Eigenschaften des Fahrzeuges erheben, das Verhalten des ICC-Systems selbst evaluieren, sowie Verfahren, welche die Kommunikationsqualität bewerten. Innerhalb jeder dieser Gruppen werden erste instrumentelle Verfahren beschrieben und validiert. Für die Entwicklung der instrumentellen Verfahren zur Schätzung der Qualität wird eine Qualitätsreferenz, welche das subjektive Empfinden von Passagieren abbildet, benötigt. Zu diesem Zwecke werden neben den instrumentellen Verfahren auch einige auditive Evaluierungsverfahren vorgestellt und deren Ergebnisse analysiert worden. Hierfür werden psychoakustische Perzeptionsexperimente durchgeführt und analysiert

Commercial soundscape: propuesta de un método de aproximación a la caracterización de un paisaje sonoro comercial en la ciudad

In recent years, the sound is lawfully present in urban and architectural projects through new regulations approved acoustic. But also in the field of research which studies the characterization of a fuller sound. In various published researches it has shown that the simple measurement of sound intensity (dB) is not sufficient to characterize the soundscape (soundscape) of a place. Therefore it is necessary to understand a soundscape in a better way and develop methods that allow a more complete characterization thereof. Several investigators have developed multicriteria methods for this characterization. One of the main elements that characterize a soundscape are the activities that exist in the urban environment of the soundscape. Most urban activities generate sound; some of these activities need that sound to create an environment to their own development and other need instead of silence for their development. The objective of this Thesis is to investigate whether it is possible to establish a correlation which allows for an urban activity, in this case the commerce, with the soundscape and the urban environment in which the soundscape develops. Finding a pattern of behavior from three aspects: urban activity (COMMERCE), the urban environment where the activity exists (PHYSICAL ENVIRONMENT: physical, facades height, width of road, rail, etc.) and the sound produced in that place (SOUNDSCAPE). Each of the three areas has been measured or characterized by indicators. An important part of this Thesis has been devoted to seek and propose these indicators. The same indicators have later used to compare different urban places to assess the correlation between the three aspects. The proposed methodology can be divided into two parts: a first part dedicated to the creation of a theoretical framework based on background and bibliographic references of previous researches. And a second part based on campaign records, field work, a total of four records Campaigns (PHASES) have been carried out. Each phase has consisted of several urban places. In each place, the indicators have been collected (sound, commercial and physical) depending on the phase. For each stage of each campaign has made a file, where each indicator has been collected. It has been collected 38 places were chosen over four campaigns of records in three different cities: The first records campaign held in Melbourne Australia). The second campaign held in Logroño (Spain). Third campaign held in Barcelona (Spain). Fourth campaign held in Barcelona (Spain). Throughout the campaigns have been identified, proposed and evaluated different indicators. The indicators and how to pick them "in situ" also have been developed over the campaigns. The nature of these indicators has been as follows: Commercial Indicators (COMMERCE): variables that have collected data related to commerce (such as commercial intensity per meter of facade or typologies of commerce) and social activities that are generated in the place. Physical indicators (PHYSICAL ENVIRONMENT): variables that have gathered physical data in the place analyzed. And acoustic indicators (SOUNDSCAPE): Variables that collected the recorded sound in each place. These variables were based on the analysis of two acoustic measurements: the frequency spectrum and spectrogram. This Thesis has shown the need for a multicriteria method to develop any urban acoustic project, due to the complexity of the elements that configure a soundscape. It has also shown it is difficult to establish a clear correlation between the three aspects proposed. It has proved essential to establish the conditions of field study, since the external acoustic, unlike the interior, presents problems in limiting the area of places analyzed. These terms refer to the physical and temporal boundaries of the study area. As it has shown in this Thesis, the temporal aspect has a significant influence on their characterization.En los últimos años la acústica se hace presente legalmente en proyectos urbanos y arquitectónicos a través de las nuevas normativas acústicas aprobadas. Pero también en el campo de la investigación dónde se estudia la caracterización de una acústica mas completa. En diversas investigaciones publicadas se ha demostrado que la simple medición de la intensidad sonora (dB) no es suficiente para caracterizar el soundscape (paisaje sonoro) de un lugar. Uno de los principales elementos que caracterizan un soundscape son las actividades que tienen lugar en el escenario urbano de dicho soundscape. Algunas de ellas necesitan de ese sonido para crear un ambiente que favorezca su propio desarrollo y otras en cambio precisan de silencio para su desarrollo. El objetivo de esta Tesis es investigar si es posible establecer una correlación que permita relacionar una actividad urbana, en este caso el Comercio, con el soundscape y el escenario urbano en el que se desarrolla. Buscar patrones de comportamiento entre tres aspectos: la actividad urbana (COMERCIO), el escenario urbano dónde se desarrolla dicha actividad (ENTORNO FÍSICO) y la acústica que se produce en ese escenario (SOUNDSCAPE). Cada uno de los tres aspectos se ha caracterizado por medio de indicadores. Una parte importante de esta Tesis se ha dedicado a buscar y proponer estos indicadores, que luego han servido para comparar diferentes escenarios urbanos para valorar la relación entre estos tres aspectos. La metodología propuesta se divide en dos partes: una primera, dedicada a la creación de un marco teórico basado en referencias de investigaciones anteriores. Y una segunda parte dedicada a realizar cuatro Campañas de registros (FASES). Cada FASE ha constado de varios escenarios urbanos. En cada escenario, se han recogido los indicadores (sonoros, comerciales y físicos) que hasta esa campaña se habían propuesto. Para cada escenario de cada campaña se ha realizado una ficha, dónde se ha recogido cada indicador. Se han escogido 38 escenarios repartidos en cuatro campañas de registros en tres ciudades diferentes: La Primera campaña de registros llevada a cabo en Melbourne (Australia). La Segunda campaña llevada a cabo en Logroño (España). Tercera campaña llevada a cabo en Barcelona (Cataluña). Cuarta campaña llevada a cabo en Barcelona (Cataluña) A lo largo de las campañas se han identificado, propuesto y valorado diferentes indicadores. Los indicadores y el modo de recogerlos ¿in situ¿ también se han ido desarrollando a lo largo de las campañas. La naturaleza de estos indicadores ha sido la siguiente: Indicadores Comerciales (Actividad comercial): variables relacionadas con el comercio (cómo la intensidad comercial por metro de fachada o las tipologías de comercio) y las actividades sociales que se generan en el escenario. Indicadores Físicos (Entorno Físico), variables como la anchura de la vía, altura de las fachadas, porcentaje de asfalto respecto de las aceras. Datos que caractericen la apariencia material del escenario estudiado. E Indicadores Sonoros (Soundscape): variables del sonido registrado en cada escenario. Estas últimas se han basado en el análisis de dos mediciones acústicas: el espectro de frecuencias y el espectrograma. Esta Tesis ha mostrado la necesidad un método multicriteria para acometer cualquier proyecto acústico urbano, debido a la complejidad de los elementos que configuran un soundscape. También ha mostrado que es difícil establecer una correlación clara entre los tres aspectos propuestos. Se ha revelado como fundamental establecer las condiciones de estudio de campo, ya que la acústica exterior, al contrario de la interior, presenta problemas a la hora de limitar las zonas de estudio de campo. Estas condiciones hacen referencia a los límites físicos de la zona estudiada y los limites temporales. Ya que como se ha mostrado en esta Tesis el aspecto temporal influye de manera determinante en su caracterización.Postprint (published version

Adaptive Feedback Cancellation in Hearing Aids

Acoustic feedback is a well-known phenomenon in hearing aids and public address systems. Under certain conditions it causes the so-called howling effect, which is highly annoying for the hearing aid user and limits the maximum amplification of the hearing aid. The most common choice to prevent howling is the adaptive feedback cancellation algorithm, which is able to completely eliminate the feedback signal. However, standard adaptive feedback cancellation algorithms suffer from a biased adaptation if the input signal is spectrally colored, as it is for speech and music signals. Due to this bias distortion artifacts (entrainment) are generated and consequently, the sound quality is significantly reduced. Most of the known methods to reduce the bias have focused on speech signals. However, those methods do not cope with music, since the tonality and correlation are much stronger for such signals. This leads to a higher bias and consequently, to stronger entrainment for music than for speech. Other methods, which deal with music signals, work only satisfactorily when using a very slow adaptation speed. This reduces the ability to react fast to feedback path changes. Hence, howling occurs for a longer time when the feedback path is changing. In this thesis, a new sub-band adaptive feedback cancellation system for hearing aid applications is proposed. It combines decorrelation methods with a new realization of a non-parametric variable step size. The adaptation is realized in sub-bands which decreases the computational complexity and increases the adaptation performance of the system simultaneously. The applied decorrelation methods, prediction error filter and frequency shift, are well known approaches to reduce the bias. However, the combination of both is first proposed in this thesis. To apply the proposed step size in the context of adaptive feedback cancellation, a method to estimate the signal power of the desired input signal, i.e., without feedback, also referred to as source signal power is necessary. This estimate is theoretically derived and it is demonstrated that it is a reliabe estimate if the decorrelation methods are additionally applied. In order to further improve the performance of the system three additional control methods are derived: The first one is an impulse detection to detect wideband impulses, which could lead to misadaptation. Secondly, a modified estimate of the source signal power to stabilize the system in case of jarring voices is proposed. Lastly, a correlation detection, which is applied to improve the trade-off between adaptation stability and tracking behavior, is developed. The complete system is optimized and evaluated for several speech and music signals as well as for different feedback scenarios in simulations with feedback paths measured under realistic situations. Additionally, the system is tested by real-time simulations with hearing aid dummies and a torso and head simulator. For both simulation setups hearing loss compensation methods as applied in realistic hearing aids are used. The performance is measured in terms of being able to prevent entrainment (adaptation stability) and reacting to feedback path changes (tracking behavior). The complete adaptive feedback cancellation system shows an excellent performance. Furthermore, the system relies only on few parameters, shows a low computational complexity, and therefore has a strong practical relevance

Beiträge zu breitbandigen Freisprechsystemen und ihrer Evaluation

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 hereby acts as device under test (DUT) and is thoroughly investigated, which will show the DUT’s satisfying performance, as well as the advantages of the proposed development process. As current methods for the evaluation of HFS’s in dynamic conditions oftentimes still lack flexibility, reproducibility, and accuracy, this work introduces “Car in a Box” (CiaB) as a novel, improved system for this demanding task. It is able to enhance the development process by performing high-resolution system identification of dynamic electro-acoustical systems. The extracted dyn. impulse response trajectories are then applicable to arbitrary input signals in a synthesis operation. A realistic dynamic automotive auralization of a car cabin interior is available for HFS evaluation. It is shown that this system improves evaluation flexibility at guaranteed reproducibility. In addition, the accuracy of evaluation methods can be increased by having access to exact, realistic imp. resp. trajectories acting as a so-called “ground truth” reference. If CiaB is included into an automotive evaluation setup, there is no need for an acoustical car interior prototype to be present at this stage of development. Hency, CiaB may ease the HFS development process. Dynamic acoustic replicas may be provided including an arbitrary number of acoustic car cabin interiors for multiple developers simultaneously. With CiaB, speech enh. system developers therefore have an evaluation environment at hand, which can adequately replace the real environment.Diese Arbeit beschäftigt sich mit der Weiterentwicklung breitbandiger Freisprechsysteme für mono-/stereophone Anwendungsfälle und liefert innovative Beiträge zu deren Qualitätsmessung. Die vorgestellten Verfahren basieren auf im Frequenzbereich adaptierenden Algorithmen zur Systemidentifikation gemäß Kalman-Theorie in einer Zustandsraumdarstellung. Es werden funktionale Erweiterungsmodule dahingehend entwickelt, dass mindestens eine Qualitätsanforderung verbessert wird, ohne andere eklatant zu verletzen. Diese nach Anforderung flexibel kombinierbaren algorithmischen Erweiterungen werden gemäß Empfehlungen der ITU-T (Rec. P.1110/P.1130) in vorwiegend automotiven Testszenarien getestet und somit deren zielgerichtete Wirksamkeit bestätigt. Es wird eine Methodensammlung und ein technisches System zur verbesserten Prototypentwicklung/Evaluation von automotiven Freisprech- und Innenraumkommunikationssystemen vorgestellt und beispielhaft mit dem monophonen Freisprechsystem in diversen Ausbaustufen zur Anwendung gebracht. Daraus entstehende Vorteile im Entwicklungs- und Testprozess von Sprachverbesserungssystem werden dargelegt und messtechnisch verifiziert. Bestehende Messverfahren zum Verhalten von Freisprechsystemen in zeitvarianten Umgebungen zeigten bisher oft nur ein unzureichendes Maß an Flexibilität, Reproduzierbarkeit und Genauigkeit. Daher wird hier das „Car in a Box“-Verfahren (CiaB) entwickelt und vorgestellt, mit dem zeitvariante elektro-akustische Systeme technisch identifiziert werden können. So gewonnene dynamische Impulsantworten können im Labor in einer Syntheseoperation auf beliebige Eingangsignale angewandt werden, um realistische Testsignale unter dyn. Bedingungen zu erzeugen. Bei diesem Vorgehen wird ein hohes Maß an Flexibilität bei garantierter Reproduzierbarkeit erlangt. Es wird gezeigt, dass die Genauigkeit von darauf basierenden Evaluationsverfahren zudem gesteigert werden kann, da mit dem Vorliegen von exakten, realen Impulsantworten zu jedem Zeitpunkt der Messung eine sogenannte „ground truth“ als Referenz zur Verfügung steht. Bei der Einbindung von CiaB in einen Messaufbau für automotive Freisprechsysteme ist es bedeutsam, dass zu diesem Zeitpunkt das eigentliche Fahrzeug nicht mehr benötigt wird. Es wird gezeigt, dass eine dyn. Fahrzeugakustikumgebung, wie sie im Entwicklungsprozess von automotiven Sprachverbesserungsalgorithmen benötigt wird, in beliebiger Anzahl vollständig und mind. gleichwertig durch CiaB ersetzt werden kann