This thesis studies the soundscapes of five different urban courtyards in Västerås, Sweden and presents suggestions on how to improve them. Due to the increasing urbanization there is now an increased need for housing in cities, this leads to buildings that are close to both other buildings, roads and noise emitting activities. On the grounds of that there is now a higher amount of effort required to make urban courtyards a somewhat quiet and tranquil space. The need for such a courtyard is due to the negative health effects connected to a bad soundscape. Noise pollution can lead to both hearing loss and cardio-vascular diseases. The study was done by first conducting a research of the scientific literature about the subject and then making measurements and observations at the courtyards. The soundscapes of the studied courtyards ranged from annoying to pleasing and comfortable. The sound levels measured from 46 to 57 dBA, this difference of 11 dBA is perceived as about twice as loud by the human ear. To solve the issue with noise pollution we suggest a variety of solutions to the different courtyards. These mainly include noise barriers, green walls and roof, vegetation and sound masking techniques. The main conclusions are that even the best performing courtyard could be acoustically enhanced and that solutions that employ vegetation both reduce the sound level and introduce natural sounds that are pleasing to most humans.

An active noise control (ANC) system has been applied to the problem of attenuating low-frequency tonal noise inside small enclosures. The intended target application of the system was the reduction of the engine firing frequency inside heavy equipment cabins. The ANC system was based on a version of the filtered-x LMS adaptive algorithm, modified for the minimization of acoustic energy density (ED), rather than the more traditional minimization of squared acoustic pressure (SP). Three loudspeakers produced control signals within a mock cabin composed of a steel frame with plywood sides and a Plexiglas® front. An energy density sensor, capable of measuring acoustic pressure as well as acoustic particle velocity, provided the error signal to the control system. The ANC system operated on a single reference signal, which, for experiments involving recorded tractor engine noise, was derived from the engine's tachometer signal. For the low frequencies at which engine firing occurs, experiments showed that ANC systems minimizing ED and SP both provided significant attenuation of the tonal noise near the operator's head and globally throughout the small cabin. The tendency was for ED control to provide a more spatially uniform amount of reduction than SP control, especially at the higher frequencies investigated (up to 200 Hz). In dynamic measurement conditions, with a reference signal swept in frequency, the ED control often provided superior results, struggling less at frequencies for which the error sensor was near nodal regions for acoustic pressure. A single control channel often yielded performance comparable to that of two control channels, and sometimes produced superior results in dynamic tests. Tonal attenuation achieved by the ANC system was generally in excess of 20 dB and reduction in equivalent sound level for dynamic tonal noise often exceeded 4 dB at the error sensor. It was shown that temperature changes likely to be encountered in practice have little effect on the initial delay through the secondary control path, and are therefore unlikely to significantly impact ANC system stability in the event that a fixed set of system identification filter coefficients are employed.

Many companies implemented remote work procedures during the pandemic and for many organizations video meetings have since remained a staple. Remote working has enabled employees to be more flexible with their schedules and technical solutions such as live captioning has been identified as potentially enabling deaf/hard-of-hearing employees during meetings. However with new procedures comes concern about how we potentially can be affected by the changes. Some earlier research has shown that speech intelligibility can be improved by the inclusion of text support, but they also raised the possibility that it could have unwanted adverse effects on cognitive abilities (Zhong, Noud et al., 2022). This study was conducted with this focus, studying the effects of text support on specifically listening effort and comprehension during normal as well as adverse conditions (featuring added noise). To investigate the effects of text support a 2 (Noise, No Noise) x 2 (Text Support, No Text Support) design was used. The participants were shown 16 short videos simulating video meetings and after each video were asked to rate their perceived listening effort as well as a comprehension question about the contents of the discussion. Each of the four conditions were equally represented but the order of the specific video files and conditions that applied were randomised for each participant to mitigate undue effects. The results of the study indicate that the presence of captions decrease effort and raise comprehension in both normal and adverse conditions. Noise was found to strongly effect the listening effort required by participants but no significant effect was found upon comprehension. Some concerns regarding the ecological validity were identified during the course of the study such as only studying energetic noise and unrealistic presentation of captions. However the results are nonetheless believed to be generalizable in most regards and showcase that captions can have a positive influence during video meetings.

This report analyzes the difference between discriminative and generative image classifiers when tested on noise. The generative classifier was a maximum-likelihood based classifier using a normalizing flow as the generative model. In this work, a coupling flow such as RealNVP was used. For the discriminative classifier a convolutional network was implemented. A detailed description of how these classifiers were implemented is given in the report. The report shows how this generative classifier outperforms the discriminative classifier when tested on adversarial noise. However, tests are also conducted on salt and pepper noise and Gaussian noise, here the results show that the generative classifier gets outperformed by the discriminative classifier. Tests were also conducted on Gaussian noise once both classifiers had been trained on Gaussian noise, the results from these tests show that the discriminative classifier performs significantly better once trained on Gaussian noise. However, the generative classifier does only show marginal increases in performance and performs worse on clean data once trained on Gaussian noise. / Den här rapporten analyserar skillnaden mellan diskriminativa och generativa modellklasser för bildigenkänning när de testas på brus. Den generativa modellklassen var en maximum-likelihood baserad generativ klassifikationsmodell. Inom detta arbete användes kopplingsflödet RealNVP. För den diskriminativa bildigenkänningsmodellen så implementerades ett faltningsnätverk. En detaljerad beskrivning för hur dessa bildigenkänningsmodeller genomfördes är given i rapporten. Rapporten visar hur den generativa modellklassen överträffar den diskriminativa modellklassen när de testas på adversarialt brus. Testerna utförs emellertid med salt och peppar brus och Gaussiskt brus, för dessa visar resultaten att den generativa modellklassen överträffas av den diskriminativa modellklassen. Den generativa modellklassen visar emellertid endast marginella ökningar i prestanda, och har en sämre prestanda på ren data efter att den tränats på Gaussiskt brus. / Kandidatexjobb i elektroteknik 2022, KTH, Stockholm

No description available.

Digital Signal Processing has been dominated by the Fourier transform since the Fast Fourier Transform (FFT) was developed in 1965 by Cooley and Tukey. In the 1980's a new transform was developed called the wavelet transform, even though the first wavelet goes back to 1910. With the Fourier transform, all information about localized changes in signal features are spread out across the entire signal space, making local features global in scope. Wavelets are able to retain localized information about the signal by applying a function of a limited duration, also called a wavelet, to the signal. As with the Fourier transform, the discrete wavelet transform has an inverse transform, which allows us to make changes in a signal in the wavelet domain and then transform it back in the time domain. In this thesis, we have investigated the filtering properties of this technique and analyzed its performance under various settings. Another popular application of wavelet transform is data compression, such as described in the JPEG 2000 standard and compressed digital storage of fingerprints developed by the FBI. Previous work on filtering has focused on the discrete wavelet transform. Here, we extended that method to the stationary wavelet transform and found that it gives a performance boost of as much as 9 dB over that of the discrete wavelet transform. We also found that the SNR of noise filtering decreases as a frequency of the base signal increases up to the Nyquist limit for both the discrete and stationary wavelet transforms. Besides filtering the signal, the discrete wavelet transform can also be used to estimate the standard deviation of the white noise present in the signal. We extended the developed estimator for the discrete wavelet transform to the stationary wavelet transform. As with filtering, it is found that the quality of the estimate decreases as the frequency of the base signal increases. Many interesting signals are self-similar, which means that one of their properties is invariant on many different scales. One popular example is strict self-similarity, where an exact copy of a signal is replicated on many scales, but the most common property is statistical self-similarity, where a random segment of a signal is replicated on many different scales. In this work, we investigated wavelet-based methods to detect statistical self-similarities in a signal and their performance on various types of self-similar signals. Specifically, we found that the quality of the estimate depends on the type of the units of the signal being investigated for low Hurst exponent and on the type of edge padding being used for high Hurst exponent. / Master of Science

Master of Science / Department of Industrial & Manufacturing Systems Engineering / Malgorzata J. Rys / Centerline rumble strips (CLRS) are raised or indented patterns installed in the center of undivided rural two-lane highways. Their main function is to alert drivers who are encroaching or leaving the intended travel lane, by producing vibration and noise when crossed by vehicles’ tires. CLRS have been demonstrated to be an effective way in reducing head on and opposite direction sideswipe on two-lane highways (cross-over accidents). However, there are some disadvantages in their utilization, such as the exterior noise created by the strips, which may disturb residents in the highway vicinity. The objective of this study was to verify if the amount of noise created by CLRS is enough to impact negatively on residences and businesses, and to discover if the mean level of noise created by CLRS is statistically different than the noise generated by vehicles driving over smooth pavement. Two types of vehicles were driven over two different patterns of milled-in CLRS (rectangular and football-shaped) and over smooth asphalt pavement, at two different speeds. Researchers collected the noise levels at three distances 50, 100, and 150 feet, measured orthogonally from the center line, in 8 different open space locations. Results indicate that vehicle type, vehicle speed, pavement type, location and distances affect the levels of noise. In addition, both football and rectangular CLRS produced significantly higher levels of noise as compared to the smooth asphalt pavement. A 15 passenger van produced higher levels of noise in comparison with a sedan. Moreover, lower the vehicle speed, noise levels were lower. At every 50 feet of distance, the noise levels dropped significantly. CLRS do increase levels of noise relative to smooth pavement at distances up to 150 feet.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Missile instrumentation systems designers are constantly striving to achieve better performance out of their systems. Optimizing the antenna coverage and decreasing the noise figure are constantly strived for in order to improve system performance. At the same time, weapon systems are becoming smaller with the resulting reduced area for instrumentation. One way to achieve a lower system noise figure is to have the limiter, filter, and amplifier (LFA) located as close to the antenna as possible. This can be achieved by integrating the LFA into the substrate of a conformal wraparound antenna. Not only does this decrease the system noise, but it also saves space in an already crowded missile instrumentation section. This paper details the latest efforts in accomplishing this integration.

International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper describes a kind of Microwave Digital Frequency Synthesizer used for S-band telemetry receivers. As well known many modern electronic systems employ a Frequency Synthesizer whose spectral purity is critical. The characteristics of a PLL (Phase-Locked Loop) Frequency Synthesizer, such as frequency resolution, phase noise, spurious suppression and switch time, should be compromised in our design. A heterodyne Frequency Synthesis is often considered as a good approach to solve the problem. But it is complicated in structure and circuit. A variable-reference-driven PLL Frequency Synthesizer was introduced which can give an improved trade-off among frequency resolution, phase noise, spurious suppression. In this paper the phase noise and spurious suppression characteristic of variable-reference-driven PLL Frequency Synthesizer is analyzed theoretically and compared with that of the heterodyne Frequency Synthesizer. For engineering application, a practical Microwave Digital Frequency Synthesizer used for telemetry receiver has been designed, which is characterized by simply structure, low phase noise and low spurious output. The output spectrum of experimental measurements is given.

Aircraft noise, for the first time in Thailand, has gained public attention as a significant environmental issue since Bangkok s Suvarnabhumi Airport opened in 2006. Residential areas around the airport are expanding rapidly while local residents are protesting about the noise from the new airport which suggests a tension between economic benefits and environmental problems at the airport. This thesis sets out to obtain valuation of aviation externalities at Suvarnabhumi airport using the stated choice method. It is the first study to obtain and compare valuations from perspectives of the polluters (Thai air passengers) and the polluted (residents) at the same airport. Furthermore, this is the first study to obtain a valuation of local impacts from aircraft operations and from air passengers. It starts by investigating perceptions and awareness of the benefits and costs of aviation activities among Suvarnabhumi s residents and passengers using focus groups and questionnaires. It then employs the stated choice method to elicit willingness-to-pay (WTP) and willingness-to-accept (WTA) values of aviation externalities. The results found that the perceived environmental problems at Suvarnabhumi airport are in line with the literature mainly involving aircraft noise and its effects. This study also found that the development of the airport and surrounding area, while creating business and employment opportunities, has also created traffic and flooding problems. In terms of air pollution from aircraft, residents concerns are confined to local impacts from aircraft. Thai air passengers were found to be more concerned with engine pollution than noise. These findings were reflected in the values obtained. Two stated choice designs were used to elicit values. The first rerouted the aircraft flight path away from residents homes thus reducing aircraft noise and pollution in the area. This design also included travel time to place of work or to the shops. The rerouting attribute was not statistically significant. However, the travel time attribute reveals that residents were willing to accept 14.23 baht a month to have their travel time to work or shopping increased by 1%. The second design was used to obtain and compare values between Suvarnabhumi s residents and air passengers. In this design, attributes for aircraft noise, local air pollution and carbon emissions were included. Residents willingness to pay to reduce aircraft noise by 1% is 104.76 baht/year whereas passengers are willing to pay less, at 70.63 baht per year. Air passengers place a higher value on local air pollution than the residents. Passengers are willing to pay 97.72 baht to reduce local pollution by 1% per year, whereas residents willingness to pay is 45.36 baht. Lastly, passengers WTP to offset carbon is 473.26 baht per flight, whereas residents carbon offset coefficient is not statistically significant. The obtained values are well within the range of existing studies on aircraft noise and carbon emission valuations. Findings from this study suggest that current mitigation measures at Suvarnabhumi airport are still inadequate. There are areas where the situation is likely to get worse given the rapid growth in aviation activities and urban development at the airport. The values from this study may be used to help form the basis of fairer and more transparent compensation system alongside an operational mitigation policy to address aviation impacts. On the passenger side, the stated willingness-to-pay to reduce the impact gives an opportunity for the Thai aviation industry to promote an environmentally friendly behaviour among the travelling public.