Kolloquium
It will be presented the first steps of the research to create a methodology to measure the degree of diffuseness of the sound filed, i.e. how close a real sound field is to a ideal diffuse field. The method that will be proposed aims not just to overcome the difficulties of qualifying a room as reverberant, but also to identify the main characteristics of the sound field of a room, allowing to choose the most appropriate acoustic treatment to be adopted to achieve the desired acoustic comfort. The main objective of this first part of this work is to design a measurement structure based on spherical microphone arrays. The processing technique used is a combination of the beamforming algorithm with the Wavelet Transform. In order to ensure high number of measurement points using only few sensors, it was chosen to use a rotating microphone array that makes it possible to capture information from the sound field at 98 points measurements on the virtual surface of a sphere. Measurements and simulations are made and the results are compared with each other in order to test the efficiency of the built system.
To perform realistic sound insulations and sound renderings for building structures in virtual scenes the different building elements should be modelled individually in accordance to their material properties, rather than just being processed as single homogeneous plates.
The goal of this study is to model the airborne excitation from an oblique incident sound wave for the outer walls of a building considering only the direct sound field. Moreover, a closer examination will be conducted of the influence that the outdoor source position has on the sound insulation and sound radiation properties of the structure walls. Finally, for measurement purposes an implementation of filters for the auralization will follow.
Im Rahmen des Masterstudiengangs Elektrotechnik, Informationstechnik und Technische Informatik wurde ein sechsmonatiges Praktikum in der Abteilung Research & Innovation bei der Sennheiser electronic GmbH & Co. KG in der Wedemark verbracht. In diesem Vortrag wird das Unternehmen vorgestellt und von den Tätigkeiten, dem Arbeitsumfeld und dem sonstigen Leben in der Region Hannover berichtet. Zu den Hauptaufgaben zählten die Implementierung und Durchführung von Messungen nichtlinearer Eigenschaften elektroakustischer Wandler und der Aufbau, die Programmierung und die Inbetriebnahme verschiedener Messmethoden zur Charakterisierung der Schallübertragung luftdurchlässiger Materialien.
Außenohrübertragungsfunktionen (engl. Head-related transfer functions, HRTFs) beschreiben den Filterprozess des am Ohr eintreffenden Schalls durch Reflexionen, Brechungen, Beugungen, Interferenzen und Resonanzen. Die HRTFs besitzen einen richtungsabhängigen Anteil und unterscheiden sich außerdem von Person zu Person.
Ein neues schnelles Messsystem für HRTFs wird am Institut für Technische Akustik verwendet. Viele Ursachen können jedoch die Messungen individueller HRTFs beeinflussen, z.B. Probandenbewegung.
Ziel dieser Arbeit ist es, die Messgenauigkeit bzw. die Wiederholbarkeit zu untersuchen. Der Schwerpunkt ist die Analyse der Veränderung des Frequenzspektrums für jeweils die gleiche Richtung bei wiederholten HRTF-Messungen für jeweils eine Person. Dazu wird eine Pol-Nullstellen-Analyse verwendet, um die Maxima und Minima vom Frequenzspektrum zu approximieren. Verschiedene Verfahren können dafür eingesetzt werden, beispielsweise mit dem Ziel, die logarithmische Differenz zwischen der rekonstruierten und der gemessenen HRTF zu minimieren. Um Fehler bzw. Unterschiede zwischen HRTFs zu bewerten, wird in dieser Arbeit ein Datensatz von gemessenen HRTFs verwendet.
Rooms are often characterised by room acoustic metrics which help to categorize them by required standards. Through a previous work sound elds have been sampled in set grids and datasets have been generated. It has been shown that as an example the change in the clarity index C80 between measurement positions next to each other may already exceed the just noticeable threshold of 1dB. As a common experience it is unlikely to perceive a di erence while for example moving along a row of seats in a concert hall. The reproducibility of measurements is problematic since small di erences in measurement positions may already lead to an uncertainty. GUM, the guide to expression of uncertainties in measurement, o ers a framework which is used to estimate a model function accounting for a number of in uence quantities.
According to the formulation stage of the GUM framework one approach to estimate a model function is to nd a mean value which associates any given input distance between two microphones with an expected variation in a discussed metric. Using the dataset any sampling position can be compared with each other to evaluate metrics as a function of frequency and bandwidth. The sampling locations are uncertain themselves and have to be accounted for in a re ned model function. The distance between the microphones serve as input quantity while the average change of the examined metric is estimated as output quantity. In reference to GUM’s calculation stage the model function can be used to describe the propagation of measurement uncertainties. Since the measurement function may be not strictly linear the resulting output distribution is distorted. Using Monte-Carlo simulations these newly distorted distribution functions can be estimated. The conclusion is that boundaries for the measurement accuracy in dependence of a tolerable uncertainty can be established.
The aim of the present thesis is to examine the cognitive control mechanisms underlying auditory selective attention by considering the influence of variables that increase the complexity of an auditory scene. Therefore, technical aspects such as dynamic binaural hearing, room acoustics and head movements as well as those that influence the efficiency of cognitive processing are taken into account. Step-wise a well-established dichotic-listening paradigm is extended into a “realistic” spatial listening paradigm.
Conducted empirical surveys are based on a dichotic-listening paradigm examining the intentional switching of auditory selective attention. Spoken phrases are simultaneously presented by two speakers to participants from two of eight azimuthal positions. The stimuli are phrases that consist of a single digit (1 to 9, excluding 5), in some experiments followed by either the German direction “UP” or “DOWN”. A visual cue indicates the target’s spatial position, prior to auditory stimulus onset. Afterwards, participants are asked to identify whether the target number is arithmetically smaller or greater than five and to categorize the direction. Reaction time and accuracy are performance measures. Differences of performance measures between the repetition of the target’s spatial position and the related switch (switch costs) describe the loss of efficiency associated with redirecting attention from one target’s location to another. To examine whether the irrelevant auditory information is decoded, interference in the processing of task-relevant and task-irrelevant information is created in the paradigm.
To study the binaural effects in the intentional switching of auditory selective attention, the dichotic-listening paradigm is gradually extended towards a binaural-listening paradigm representing complex dynamic acoustic scenes in the present thesis. In order to realize the extension of the paradigm towards a realistic scene various technical methods and tools need to be applied. As the listening paradigm is step-wise broadened towards realistic scenes the technical methods and tools are assessed with respect to the collected empirical results.
Using the binaural-listening paradigm, the ability to intentionally switch auditory selective attention is tested when applying different methods of spatial reproduction. Essential differences between real sources, an individual and a non-individual binaural synthesis reproduced with headphones as well as a binaural synthesis based on Cross-Talk Cancellation are found. This indicates how the loss of individual information reduces the ability to inhibit irrelevant information. Differences in performance measures occur also with regard to the target’s spatial position. Reliable findings on the spatial localization ability are confirmed applying the listening paradigm on the intentional switching of auditory selective attention. As a step towards multi-talker scenarios in realistic environments participants are tested in differently reverberating environments. Switch costs are highly affected by reverberation and the inhibition is also impaired by to be unattended information. Age-related effects are also found when applying the binaural-listening paradigm, indicating difficulties for elderly to suppress processing the distractor’s speech.
