Noise pollution

About: Noise pollution is a research topic. Over the lifetime, 4455 publications have been published within this topic receiving 67192 citations.

Noise-compensated hidden Markov models

Abstract: The technique of hidden Markov models has been established as one of the most successful methods applied to the problem of speech recognition. However, its performance is considerably degraded when the speech signal is contaminated by noise. This work presents a technique which improves the performance of hidden Markov models when these models are used in different noise conditions during the speech recognition process. The input speech signal enters unchanged to the recognition process, while the models used by the recognition system are compensated according to the affecting noise characteristics, power and spectral shape. Hence, the compensation stage is independent of the recognition stage, allowing the models to be continually adjusted. The models used in this work are from a continuous density hidden Markov algorithm, having cepstral coefficients derived from linear predictive analysis as state parameters. It is used only static features in the models in order to show that, when properly compensated for the noise, these static features contribute significantly to improve noisy speech recognition. It is observed from the results that the parameters kept their capability to discriminate among different classes of signals, indicating that, in the context of speech recognition, the use of autoregressive-derived parameters with noisy signals does not represent an impediment. A matrix-way of converting from autoregressive coefficients to normalized autocorrelation coefficients is presented. The affecting noise is assumed additive and statistically independent of the speech signal. Although the noise dealt with should also be stationary, good performance was achieved for nonstationary noise, such as operations room noise and factory environment noise. The concept of intra-word signal-to-noise ratio is presented and successfully applied. The resulting compensated models are revealed to be less dependent on the training data set when compared to the trained hidden Markov models. Due to the computational simplicity, the time required to adjust a model is significantly shorter than the time to train it.

Traffic noise pollution

Abstract: In developing country like India with the vehicle population increasing at an almarmg rate, the residents of cities are experiencing severe environmental problems that results from road traffic in particular from Automobiles. Noise from road traffic is major source of environmental pollution and it has detrimental effects on human beings. In this paper road traffic noise survey was conducted on Gwalior city roads at four sites via. Industrial, Commercial, Semi residential and completely residential. Various parameters are evaluated e.g. Noise Pollution Level, Traffic Noise Index and Equivalent sound level. Based on this study broad conclusions are presented and suggestion made to reduce noise due to traffic.

Life Cycle Cost Evaluation of Noise and Vibration Control Methods at Urban Railway Turnouts

Abstract: A focus of the railway industry over the past decades has been to research, find and develop methods to mitigate noise and vibration resulting from wheel/rail contact along track infrastructure. This resulted in a wide range of abatement measures that are available for today’s engineers. The suitability of each method must be analysed through budget and timeframe limitations, which includes building, maintenance and inspection costs and time allocation, while also aiming at delivering other benefits, such as environmental impact and durability of infrastructure. There are several situations that need noise and vibration mitigation methods, but each design allocates different priorities on a case-by-case basis. Traditionally, the disturbance caused by railways to the community are generated by wheel/rail contact sound radiation that is expressed in different ways, depending on the movement of the rolling stock and track alignment, such as rolling noise, impact noise and curve noise. More specifically, in special trackworks such as turnouts (or called “switches and crossings”), there are two types of noise that can often be observed: impact noise and screeching noise. With respect to the screeching (or flanging), its mitigation methods are usually associated with curve lubrications. In contrast, the impact noise emerges from the sound made by the rolling stock moving through joints and discontinuities (i.e., gaps), resulting in various noise abatement features to minimise such noise impact. Life cycle analysis is therefore vital for cost efficiency benchmarking of the mitigation methods. The evaluation is based on available data from open literature and the total costs were estimated from valid industry reports to maintain coherency. A 50-year period for a life cycle analysis is chosen for this study. As for the general parameters, an area with a high density of people is considered to estimate the values for a community with very strict limits for noise and vibration.

Effects of Aircraft Noise Exposure on Heart Rate during Sleep in the Population Living Near Airports

Abstract: Background Noise in the vicinity of airports is a public health problem. Many laboratory studies have shown that heart rate is altered during sleep after exposure to road or railway noise. Fewer studies have looked at the effects of exposure to aircraft noise on heart rate during sleep in populations living near airports. Objective The aim of this study was to investigate the relationship between the sound pressure level (SPL) of aircraft noise and heart rate during sleep in populations living near airports in France. Methods In total, 92 people living near the Paris-Charles de Gaulle and Toulouse-Blagnac airports participated in this study. Heart rate was recorded every 15 s during one night, using an Actiheart monitor, with simultaneous measurements of SPL of aircraft noise inside the participants’ bedrooms. Energy and event-related indicators were then estimated. Mixed linear regression models were applied, taking into account potential confounding factors, to investigate the relationship between energy indicators and heart rate during sleep measured every 15 s. Event-related analyses were also carried out in order to study the effects of an acoustic event associated with aircraft noise on heart rate during sleep. Results The more the SPL from all sources (LAeq,15s) and the SPL exceeded for 90% of the measurement period (LA90,15s) increased, the more heart rate also increased. No significant associations were observed between the maximum 1-s equivalent SPL associated with aircraft overflight (LAmax,1s) and differences between the heart rate recorded during or 15 or 30 s after an aircraft noise event and that recorded before the event. On the other hand, a positive and significant association was found between LAmax,1s and the heart rate amplitude calculated during an aircraft noise event. Results were unchanged when analyses were limited to participants who had lived more than five years in their present dwelling. Conclusion Our study shows that exposure to the maximum SPL linked to aircraft overflight affect the heart rate during sleep of residents near airports. However, further studies on a larger number of participants over several nights are needed to confirm these results.