Examensarbeten för masterexamen

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    Improved noise map accuracy by using GPS acquired vehicle speeds: study of predicted equivalent noise levels using the Nord96 and Nord2000 models
    (2022) Kondic, Marija; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Forssén, Jens; Forssén, Jens
    The noise maps in Sweden have always been constructed with the Nord 96 calculation model using the signposted speeds. This project investigates the limitations of this model, as well as what differences arise when the signposted speeds are exchanged for the real recorded vehicle speeds. In this case, the GPS acquired speeds were used. Different steps in the Nord 96 calculation model that could influence the changes in the noise maps were addressed, as well as the differences between the Nord 96 and Nord 2000 models. The influence of the percentage of heavy vehicles, different vehicles categories and importance of the acceleration of vehicles is investigated. The main goal of this paper was to investigate the possibility of creating a set of measures to be used as a correction for the current calculation model. This investigation is conducted on the subject area consisting of Kävlinge, Furulund, Löddeköpinge, and Björnstorp area. The Kävlinge area is closely investigated and the individual streets are analysed for the purpose of detecting the causes of sound pressure level differences on a small scale. Significant results were obtained, showing that difference in noise level can be up to ± 5 dB in some street segments, which is detectable by human ears. The correction of the current model is concluded not to be possible by just taking the average SPL difference for different street types and speed limits, thus the further investigation is needed.
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    Auralization of road traffic scenes: Investigating perceived effects of heavy vehicle proportion
    (2022) Zhou, Yun; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Forssén, Jens; Forssén, Jens
    For vehicles with internal combustion engines, the main types of noise when driving are tyre-road noise and propulsion noise. According to the Nord 2000 model, light and heavy vehicles have different noise levels and spectrum at different speeds. In urban traffic scenes, the number of light and heavy vehicles varies, and people may perceive the scenes differently even if they have the same equivalent A-weighted level (LAEq) but various proportions of light and heavy vehicles. To investigate the effect of the proportion of heavy vehicles on human psychological perception, the noise signals of five individual vehicles (two heavy and three light) at different speeds were auralized based on the combined model proposed in the LISTEN project and applied to compose eight traffic scene signals containing different proportions of heavy vehicles. These signals are used in the listening test where participants were asked to make category judgments and paired comparisons. The results of the category judgment part of the listening test showed that the signals containing heavy vehicles were indeed more disturbing than the signal only consisting of light vehicle noise, and scoring higher in loudness, sharpness and roughness. However, the stress and annoyance felt by the participants when listening to the signals did not increase with the proportion of heavy vehicles in the signal. From the paired comparison part of the test, it can be found that for heavy vehicles, participants felt more disturbed by the lower speed signals when the perceived loudness of the signals was constant. As for the plausibility of the traffic scene signals created, all eight signals scored similarly, between 5 and 6 on a scale of plausibility, which means that the traffic scene signals created are somewhat plausible, but still need to be improved.
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    Covariance and coherence matching for binaural room impulse responses; implementation and evaluation of rendering methods using different-order ambisonics
    (2022) Hedlund , Elin; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Ahrens, Jens; Ahrens, Jens
    Rendering binaural room impulse responses with the use of spherical microphone arrays and sets of head-related transfer functions minimize required measurements but will however exhibit a difference in perception due to, among other things, spherical harmonic truncation. By utilizing the spatial perceptually relevant interaural cues, the similarity to a directly measured BRIR could be enhanced. In this thesis, two different methods for rendering binaural room impulse responses with different-order Ambisonics are employed to evaluate and compare the similarity between the generated BRIRs and directly measured counterparts using an artificial head and torso recording. Both methods utilize inter-aural cues within the inter-aural coherence and covariance matrix, respectively, in order to process the diffuse part of the BRIR. The results show an improvement for the covariance matrix framework compared to the coherence matching method, even for rendering employing first-order Ambisonics. A pilot study in the form of an informal listening test was conducted to investigate the perceived similarity between the generated and measured BRIRs. The results of the listening test indicate that an increased spatial resolution due to higher-order Ambisonics will enhance the perceived similarity, while also displaying varying results depending on rendering method. However, a more extensive listening test would be beneficial. The findings indicate that the covariance framework with even higher-order Ambisonics would further optimize the quality and perceived similarity.
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    The investigation of eXMA method with non-spherical scatters
    (2022) Hu, Ziyi; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Ahrens, Jens; Ahrens, Jens
    The XMA was a recently presented higher-order ambisonic microphone array which is based on the spherical microphone array (SMA) and equatorial microphone array (EMA) but without a traditional spherical scattering body. Since it is compatible with the EMA, the XMAs can also be designed with the microphones placed on a circumferential contour around the scattering body, which is called the equatorial XMA (eXMA). Compared with the classical SMAs, the eXMA method reduced the required number of microphones significantly since it did not need the microphones to be distributed over the whole surface of the scatterer. The eXMA shows a good application prospect in spatial sound field recording especially when combined with the VR camera to produce a complete panoramic audio-visual experience from a first-person view. However, the eXMA has so far only been evaluated as a headmounted array, i.e. with a human head as the baffle. The performance of eXMA with other shapes of scatterers are unknown. In this work, we used the mesh2hrtf implementation of the boundary element method (BEM) to simulate eXMA calibration measurements for a variety of candidate scatterers including cylinders, cubics and some shapes that are inspired from real VR 360 cameras. We also deformed those shapes and moved up the microphone array to see the influence. Based on those simulations, we identify what spherical harmonic orders can be obtained with what accuracy for a set of convex scattering body geometries that are of relevance in the given context. We demonstrate that the shape of the body is not very critical. The eXMA shows very robust performances with the different shapes of scatterers, some of them even have corners. Reducing the height of the scatterers or moving up the microphone array to the edge will increase the error but the accuracy is still acceptable. The main limitation is the size of the scatters that small bodies do not allow for extracting higher orders at low frequencies. Limitations of the simulation are discussed and at the end we also generate some spatial audio recordings based on the cuboid and the squashed cylinder scatterers.
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    The Paraspax method applied on loudspeaker arrays: loudspeaker array-based synthesis of varying spaces including an investigation on how the sound field changes at different position within the array
    (2022) Persson, Hanna; Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik (ACE); Ahrens, Jens; Ahrens, Jens
    Binaural room impulse responses (BRIRs) describes the transmission from a sound source to a listeners left and right ear, unlike monaural room impulse responses which only contains one channel and therefore sounds the same to both ears. The first method to get BRIRs of a space is by recordings of a sound source using a dummy head with microphones in each ear for different head orientations and positions in the space. This could be both time consuming and costly and therefore research is trying to find new ways that are more practical and includes signal processing. The Paraspax method is a method for parametric spatial audio rendering with 6 DoF based on one monaural room impulse response. The method encodes monaural and spatial parameters offline into a parametric spatial sound field for arbitrary head orientations and room positions. The most important parameters are the amplitudes of the direct sound and up to 10 early reflections with corresponding times and directions of arrival (TOAs, DOAs). The TOAs are simulated from a reflection detection algorithm and the image source model provides the DOAs. These, together with the rest of the parameters, forms the basis of BRIRs synthesized for audio reproduction using headphones. The work of this thesis contains an extension of the BRIR synthesis into a loudspeaker array-based synthesis where the parametrized direct sound and early reflections are distributed over some loudspeakers arranged over a sphere. The resulting sound field is estimated for a listener positioned at different positions inside the loudspeaker array. The authors of the Paraspax have presented the method for a shoebox-shaped room but it is still unknown how it works for other environments and therefore a handful of room impulse responses will be tested. The thesis will answer what the minimum number of loudspeakers in the loudspeaker array is and how the sound field at different listening positions differs from the sound field created at the center of the array. It will also be shown how some parameters of the loudspeaker array influences the sound. Convolving an anechoic drums audio file with the synthesized sound field created by the loudspeaker array acts for virtually place the listener at different positions in the loudspeaker array and the resulting sound represents how the drums are perceived in the different environments of test. The results obtained by the loudspeaker array containing a reduced number of loudspeakers are analyzed and compared with a 84-loudspeaker array. It will be shown that the loudspeaker array is highly dependent on the simulated DOAs, and especially the azimuth angles as it will appear that the loudspeakers should be placed around the listener. If the DOAs of the early reflections are varied enough in azimuth, it shows that three loudspeakers are enough. The sound behaves differently depending on the direction in which the listener moves, but by increasing the number of loudspeakers or the radius of the array, the listener can generally move more freely with the exception of when the TOA differences between the different loudspeakers being too large.