Environmental Noise Assessment.课件

1、Environmental Noise AssessmentDuanKe YouXuda WangJingyiGuided by Allen一、 Major Task：Fistly，got the sound signal.Then transform the time- domain signal to the frequency domain through FFT,and do the cross-correlation to get the power spectral density.Then do the 1/3 octave to get a section.Finally do

2、 the A weighting to get the weighed sound level.二、BackgroundNoise pollution is the disturbing or excessive noise that may harm the activity or balance of human or animal life. The source of most outdoor noise worldwide is mainly caused by machines and transportation systems, motor vehicles, aircraft

3、, and trains.People can hear the sound which has a frequency range of 20Hz-20000Hz. And the most comfortable frequency for humans ear is about 1000Hz. Also appropriate sound intensity for human is 20dB-110dB. Sound which is beyond the frequency and intensity range can be seen as noise. Its an import

4、ant work to reduce the noise to get the ideal sound.三、The Power Spectral Density1、 DefinitionIn physics, signal is usually a wave form, such as electromagnetic wave, random vibration or sound wave. When the wave spectral density multiplied by an appropriate coefficient,it will be per unit frequency

5、power wave carrying, which is known as the signal power spectral density (power spectral density, PSD) or spectral power distribution (spectral power distribution, SPD). The power spectral density of the units are typically used in watts per Hertz (W/Hz), or the use of wavelength rather than frequen

6、cy, namely each nano watts (W/nm) to represent. The power spectral density of the signal exists if and only if the signal is generalized to the existence of stationary process. If the signal is not a stationary process, then the autocorrelation function is a function of two variables, so you don'

7、;t have the power spectral density, but we can use a similar technique to estimate the time-varying spectral density.2、 CalculationThe total power P of a signal x(t) is the following time average:The spectral density of f(t) and the autocorrelation of f(t) form a Fourier transform pair One of the re

8、sults of Fourier analysis is Parseval's theorem which states that the area under the energy spectral density curve is equal to the area under the square of the magnitude of the signal, the total energy:We used the function, pwelch, to draw the PSD of noise signal and the unit of power is Pa, so

9、to convert it into dB, we used: dB = 10*log10(Pa)四、The 1/3 Octave1、Defini5tion and CalculationThe human ear frequency range is 20Hz to 20KHz audio, makes a concrete analysis of each frequency component is not generally required in the sound signal spectrum analysis. For the sake of convenience, the

10、20Hz to audio frequency range of 20KHz is divided into several sections, each band into a frequency range. Dividing frequency range with constant bandwidth, keep on a band, lower ratio is a constant. Experiments show that, when the sound of the same sound pressure level and frequency doubled, sounds

11、 tones also doubled.Analyzing a source on a frequency by frequency basis is possible but time consumingcitation needed. The whole frequency range is divided into set of frequencies called bands. Each band covers a specific range of frequencies. For this reason, a scale of octave bands and one-third

12、octave bands has been developed. A frequency is said to be an octave in width when the upper band frequency is twice the lower band frequency. A one-third octave band is defined as a frequency band whose upper band-edge frequency (f2) is the lower band frequency (f1) times the cube root of two.五、The

13、 A Weighting.1、DefinitionA-weighting is the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. A-weighting is applied to instrument-measured sound levels in effort to accoun

14、t for the relative loudness perceived by the human ear, as the ear is less sensitive to low audio frequencies. It is employed by arithmetically adding a table of values, listed by octave or third-octave bands, to the measured sound pressure levels in dB. The resulting octave band measurements are us

15、ually added (logarithmic method) to provide a single A-weighted value describing the sound; the units are written as dB(A)The A-Weighted Sound Level is a single number measure of the relative loudness of noise that is used extensively in outdoor environmental noise standards. The ratings correlate w

16、ell with human judgments of relative loudness, but do not take into account the spectral balance or sound quality. Many different sounding spectra can result in the same numeric value, but have quite different subjective qualities. The A-Weighted Sound Level can be measured with simple sound level m

17、eters; the rating is expressed as a number followed by dB(A) or dBA. For example, 35dB(A).2、CalculationAlthough they are defined in the standards by tables with tolerance limits (to allow a variety of implementations)citation needed the weightings can be described in terms of a weighting function R_

18、X(f) that acts on the amplitude spectrum (not the intensity spectrum), or an offset X(f) that must be added to the unweighted sound level in dB units.六、The Total Sound Pressure LevelThe sound pressure level of each frequency range corresponding to the pressure energy sum total sound energy can be ob

19、tained, then the total sound pressure calculated by the following formula：七、Results1、The Noise Signal Got From Allenmid-frequencyfrequency rangeMid-frequencyfrequency range2522.42880071090031.52835.5100090011204035.5451250112014005045561600140018006356712000180022408071902500224028001009011231502800

20、355012511214040003550450016014018050004500560020018022463005600710025022428080007100900031028035510000900011200400355450125001120014000500450560160001400018000630560710  The A-Weighted Results: SPL is 90.5568dB2、The Noise Signal Got From Allen1)、The Noise Signal in BaoYugang LibraryThe A-W

21、eighted Results: SPL is 55.3230dB2)、The Noise Signal in Woods Behind the Library with ChattingThe A-Weighted Results: SPL is 85.7920dB 3)、The Noise Signal in Woods Behind the Library without ChattingThe A-Weighted Results: SPL is 58.5092dB八、SummariesThis project is not so difficult as we thought,But

22、 it is also not easy.We searched a lot of materials and articles to solve the problem. This project not only just test the knowledge that we learned, we also have trained how to grasp a thing, how to do one thing perfectly, and to do the same thing more quickly. DuanKe is the leader,and also the org

23、anizer,he does a better job than we two.And also thanks to the guidance from Teacher Huang and Allen.Without your help,we cannot finish this project so fast and so good.九、Code Used in This Projecttextread('9.csv');da_5=ans(:,5);da_1=ans(:,1);%时域信号ww = da_5;dt = 1/20000;t = (0:length(ww)-1)*d

24、t;figureplot(t,ww)xlabel('Time(t/s)')ylabel('Amptitude(A)')title('Noise Signal in woods(without chatting)')%自相关变换 频率谱密度window = rectwin(length(ww);YY,fout=pwelch(ww,window,0,length(ww),1/dt);figureplot(fout,10*log10(YY)xlabel('Frequency(f/Hz)')ylabel('Power(P/dB)')title('PSD')%1/3频程%频率范围f=22.4,28,35.5,45,56,71,90,112,140,180,224,280,355,450,560,710,900,1120,1400,1800,2240,2800,3550,4500,5600,7100,9000;%中心频率fm=25,31.5,40,50,63,80,100,125,160,200