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1、dB的定義:就物理量(電壓,聲壓)來說,dB=20*log(p/pref),其中p代表任何物理量,pref代表叁考物理量,如電壓的ref為1V,聲壓為20uPa.就能量的定義來看,dB=10*log(E/Eref),其中E代表任何能量,Eref代表叁考能量.之所以會有10與20之間的差異,在於能量正比於物理量的平方(E=1/2mv^2).各種dB的參數:dBSPL:以20uPa為參考,1Pa=94dB,為表示聲壓值最常用的參數,speaker,receiver零件的soundpressurelevel以此表示.dBA表示A加權.dBPa:以1Pa為參考
2、,1Pa=0dB,一般所看見表示聲壓值的另一種方法,microphone的感度最常用此表示,如-44dBPa/V其他我懶的打了,在此轉貼ITU-T的資料.Forabsolutepowerlevel(seeAppendixI,§I.1.1)dBW:absolutepowerlevelwithrespectto1watt,expressedindecibels;dBm:absolutepowerlevelwithrespectto1milliwatt,expressedindecibels;dBm0absolutepowerlevelwithrespect
3、to1milliwatt,expressedindecibels,referredtoapointofzerorelativelevel;dBm0p:absolutepsophometricpowerlevel(weightedfortelephony)withrespectto1milliwatt,expressedindecibels,referredtoapointofzerorelativelevel;dBm0s:absolutepowerlevelwithrespectto1milliwatt,expressedindecibels,refe
4、rredtoapointofzerorelativelevelinsoundprogrammetransmission;dBm0ps:absolutepsophometricpowerlevel(weightedforsound-programmetransmission)withrespectto1milliwatt,expressedindecibels,referredtoapointofzerorelativelevelinsoundprogrammetransmission.Forabsolutelevelofanelectromagneti
5、cfield(seeAppendixI,§I.2.1):dBμordBu:absoluteleveloftheelectromagneticfieldwithrespectto1mV/m,expressedindecibels.Forabsolutevoltagelevelincludingtheaudio-frequencynoiselevel(seeAppendixI,§§I.2.2andI.2.3):dBu:absolutevoltagelevelwithrespectto0.775V,expressedindecibels;dBu0:absol
6、utevoltagelevelwithrespectto0.775V,referredtoapointofzerorelativelevel;dBu0s:absolutevoltagelevelwithrespectto0.775V,referredtoapointofzerorelativelevelinsoundprogrammetransmission;dBqps:absoluteweightedvoltagelevelmeasuredaccordingtoRecommendation468,CCIRVolumeX-1,insound-progr
7、ammetransmission;dBq0ps:absoluteweightedvoltagelevelmeasuredaccordingtoRecommendation468,CCIRVolumeX1,referredtoapointofzerorelativelevelinsound-programmetransmission;dBq0s:absoluteunweightedvoltagelevelmeasuredaccordingtoRecommendation468,CCIRVolumeX-1,insound-programmetransmis
8、sionwithrespectto0.775Vreferredtoapointofzerore
