ISO11172ANNEXD教学提纲

1、Good is good, but better carries it.精益求精，善益求善。ISO11172ANNEXD-3-ANNEXD(informative)PSYCHOACOUSTICMODELS3-D.1.PsychoacousticModelIThecalculationofthepsychoacousticmodelhastobeadaptedtothecorrespondinglayer.ThisexampleisvalidforLayersIandII.ThemodelcanbeadaptedtoLayerIII.Thereisnoprincipaldifferenceint

2、heapplicationofpsychoacousticmodel1toLayerIorII.LayerI:Anewbitallocationiscalculatedforeachblockof12subbandor384inputPCMsamples.LayerII:Anewbitallocationiscalculatedforthreeblockstotaling36subbandsamplescorrespondingto3*384(1152)inputPCMsamples.Thebitallocationofthe32subbandsiscalculatedonthebasisof

3、thesignal-to-maskratiosofallthesubbands.Thereforeitisnecessarytodetermine,foreachsubbandthemaximumsignallevelandtheminimummaskingthreshold.TheminimummaskingthresholdisderivedfromanFFToftheinputPCMsignal,followedbyapsychoacousticmodelcalculation.TheFFTinparallelwiththesubbandfiltercompensatesforthela

4、ckofspectralselectivityobtainedatlowfrequenciesbythesubbandfilterbank.Thistechniqueprovidesbothasufficienttimeresolutionforthecodedaudiosignal(Polyphasefilterwithoptimizedwindowforminimalpre-echoes)andasufficientspectralresolutionforthecalculationofthemaskingthresholds.Thefrequenciesandlevelsofalias

5、ingdistortionscanbecalculated.Thisisnecessaryforcalculatingaminimumbitrateforthosesubbandswhichneedsomebitstocancelthealiasingcomponentsinthedecoder.Theadditionalcomplexitytocalculatethebetterfrequencyresolutionisnecessaryonlyintheencoder,andintroducesnoadditionaldelayorcomplexityinthedecoder.Thecal

6、culationofthesignal-to-mask-ratioisbasedonthefollowingsteps:Step1-CalculationoftheFFTfortimetofrequencyconversion.Step2-Determinationofthesoundpressurelevelineachsubband.Step3-Determinationofthethresholdinquiet(absolutethreshold).Step4-Findingofthetonal(moresinusoid-like)andnon-tonal(morenoise-like)

7、componentsoftheaudiosignal.Step5-Decimationofthemaskers,toobtainonlytherelevantmaskers.Step6-Calculationoftheindividualmaskingthresholds.Step7-Determinationoftheglobalmaskingthreshold.Step8-Determinationoftheminimummaskingthresholdineachsubband.Step9-Calculationofthesignal-to-maskratioineachsubband.

8、Thesestepswillbefurtherdiscussed.Asamplingfrequencyof48kHzisassumed.Fortheothertwosamplingfrequenciesallfrequenciesmentionedshouldbescaledaccordingly.Step1:FFTAnalysisThemaskingthresholdisderivedfromanestimateofthepowerdensityspectrumthatiscalculatedbya512-pointFFTforLayerI,orbya1024-pointFFTforLaye

9、rsIIandIII.TheFFTiscalculateddirectlyfromtheinputPCMsignal,windowedbyaHannwindow.Foracoincidenceintimebetweenthebit-allocationandthecorrespondingsubbandsamples,thePCM-samplesenteringtheFFThavetobedelayed:1.Thedelayoftheanalysissubbandfilteris256samples,correspondingto5.3msatthe48kHzsamplingrate.This

10、correspondstoawindowshiftof256samples.2.TheHannwindowmustcoincidewiththesubbandsamplesoftheframe.ForLayerIthisamountstoanadditionalwindowshiftof64samples,forLayerIIanadditionalwindowshiftofminus64samples.TechnicaldataoftheFFT:LayerILayerII-transformlength512samples1024samplesWindowsizeiffs=48kHz10.6

11、7ms21.3msWindowsizeiffs=44.1kHz11.6ms23.2msWindowsizeiffs=32kHz16ms32ms-Frequencyresolutionfs/512fs/1024-Hannwindow,h(i):h(i)=*0.5*1-cos2*p*(i)/(N-1)0=i=96kbit/sand0dBforbitrates96kbit/sperchannel.Step4:Findingoftonalandnon-tonalcomponentsThetonalityofamaskingcomponenthasaninfluenceonthemaskingthres

12、hold.Forthisreason,itisworthwhiletodiscriminatebetweentonalandnon-tonalcomponents.Forcalculatingtheglobalmaskingthresholditisnecessarytoderivethetonalandthenon-tonalcomponentsfromtheFFTspectrum.Thisstepstartswiththedeterminationoflocalmaxima,thenextractstonalcomponents(sinusoids)andcalculatestheinte

13、nsityofthenon-tonalcomponentswithinabandwidthofacriticalband.TheboundariesofthecriticalbandsaregiveninthetablesCRITICALBANDBOUNDARIES(Tables3-D.2a,3-D.2b,3-D.2cforLayerI;Tables3-D.2d,3-D.2e,3-D.2fforLayerII).Thebandwidthofthecriticalbandsvarieswiththecenterfrequencywithabandwidthofaboutonly0.1kHzatl

14、owfrequenciesandwithabandwidthofabout4kHzathighfrequencies.Itisknownfrompsychoacousticexperimentsthattheearhasabetterfrequencyresolutioninthelowerthaninthehigherfrequencyregion.Todetermineifalocalmaximummaybeatonalcomponentafrequencyrangedfaroundthelocalmaximumisexamined.Thefrequencyrangedfisgivenby

15、:Samplingrate:32kHzLayerI:df=125Hz0kHzf=4.0kHzdf=187.5Hz4.0kHzf=8.0kHzdf=375Hz8.0kHzf=15.0kHzLayerII:df=62.5Hz0kHzf=3.0kHzdf=93.75Hz3.0kHzf=6.0kHzdf=187.5Hz6.0kHzf=12.0kHzdf=375Hz12.0kHzf=24.0kHzSamplingrate:44.1kHzLayerI:df=172.266Hz0kHzf=5.512kHzdf=281.25Hz5.512kHzf=11.024kHzdf=562.50Hz11.024kHzf=

16、19.982kHzLayerII:df=86.133Hz0kHzf=2.756kHzdf=129.199Hz2.756kHzf=5.512kHzdf=258.398Hz5.512kHzf=11.024kHzdf=516.797Hz11.024kHzf=19.982kHzSamplingrate:48kHzLayerI:df=187.5Hz0kHzf=6.0kHzdf=281.25Hz6.0kHzf=12.0kHzdf=562.50Hz12.0kHzf=24.0kHzLayerII:df=93.750Hz0kHzf=3.0kHzdf=140.63Hz3.0kHzf=6.0kHzdf=281.25

17、Hz6.0kHzf=12.0kHzdf=562.50Hz12.0kHzfX(k-1)andX(k)=X(k+1)(ii)ListingoftonalcomponentsandcalculationofthesoundpressurelevelAlocalmaximumisputinthelistoftonalcomponentsifX(k)-X(k+j)=7dB,wherejischosenaccordingtoLayerI:j=-2,+2for2k63j=-3,-2,+2,+3for63=k127j=-6,.,-2,+2,.,+6for127=k=250LayerII:j=-2,+2for2

18、k63j=-3,-2,+2,+3for63=k127j=-6,.,-2,+2,.,+6for127=k255j=-12,.,-2,+2,.,+12for255=k=LTq(k)orXnm(k)=LTq(k)Inthisexpression,LTq(k)istheabsolutethreshold(orthresholdinquiet)atthefrequencyofindexk.ThesevaluesaregivenintheTables3-D.1a,3-D.1b,3-D.1cforLayerI;Tables3-D.1d,3-D.1e,3-D.1fforLayerII.(ii)Decimati

19、onoftwoormoretonalcomponentswithinadistanceoflessthen0.5Bark:Keepthecomponentwiththehighestpower,andremovethesmallercomponent(s)fromthelistoftonalcomponents.Forthisoperation,aslidingwindowinthecriticalbanddomainisusedwithawidthof0.5Bark.Inthefollowing,theindexjisusedtoindicatetherelevanttonalornon-t

20、onalmaskingcomponentsfromthecombineddecimatedlist.Step6:CalculationofindividualmaskingthresholdsOftheoriginalN/2frequencydomainsamples,indexedbyk,onlyasubsetofthesamples,indexedbyi,areconsideredfortheglobalmaskingthresholdcalculation.ThesamplesusedareshowninTables3-D.1a,3-D.1b,3-D.1cforLayerI;Tables

21、3-D.1d,3-D.1e,3-D.1fforLayerII.LayerI:Forthefrequencylinescorrespondingtothefrequencyregionwhichiscoveredbythefirstsixsubbandsnosubsamplingisused.Forthefrequencyregioncorrespondingtothenextsixsubbandseverysecondspectrallineisconsidered.Finally,inthecaseof44.1and48kHzsamplingrates,inthefrequencyregio

22、ncorrespondingtotheremainingsubbands,everyfourthspectrallineisconsideredupto20kHz.Inthecaseof32kHzsamplingrate,inthefrequencyregioncorrespondingtotheremainingsubbands,everyfourthspectrallineisconsideredupto15kHz(SeealsoTables3-D.1a,3-D.1b,3-D.1cFrequencies,CriticalBandRatesandAbsoluteThresholdforLay

23、erI.)LayerII:Forthefrequencylinescorrespondingtothefrequencyregionwhichiscoveredbythefirstthreesubbandsnosubsamplingisused.Forthefrequencyregionwhichiscoveredbynextthreesubbandseverysecondspectrallineisconsidered.Forthefrequencyregioncorrespondingtothenextsixsubbandseveryfourthspectrallineisconsider

24、ed.Finally,inthecaseof44.1and48kHzsamplingrates,intheremainingsubbandseveryeighthspectrallineisconsideredupto20kHz.Inthecaseof32kHzsamplingrate,inthefrequencyregioncorrespondingtotheremainingsubbands,everyeighthspectrallineisconsideredupto15kHz.(SeealsoTables3-D.1d,3-D.1e,3-D.1fFrequencies,CriticalB

25、andRatesandAbsoluteThresholdforLayerII.)Thenumberofsamples,i,inthesubsampledfrequencydomainisdifferentdependingonthesamplingratesandlayers.32kHzsamplingrate:i=108forLayerIandi=132forLayerII44.1kHzsamplingrate:i=106forLayerIandi=130forLayerII48kHzsamplingrate:i=102forLayerIandi=126forLayerIIToeveryto

26、nalandnon-tonalcomponenttheindexiinthesubsampledfrequencydomainisassigned,whichisclosestinfrequencytotheoriginalspectrallineX(k).ThisindexiisgiveninTables3-D.1a,3-D.1b,3-D.1cforLayerI;Tables3-D.1d,3-D.1e,3-D.1fforLayerII,Frequencies,CriticalBandRatesandAbsoluteThreshold.Theindividualmaskingthreshold

27、sofbothtonalandnon-tonalcomponentsaregivenbythefollowingexpression:LTtmz(j),z(i)=Xtmz(j)+avtmz(j)+vfz(j),z(i)dBLTnmz(j),z(i)=Xnmz(j)+avnmz(j)+vfz(j),z(i)dBInthisformulaLTtmandLTnmaretheindividualmaskingthresholdsatcriticalbandratezinBarkofthemaskingcomponentatthecriticalbandratezminBark.Thevaluesind

28、Bcanbeeitherpositiveornegative.ThetermXtmz(j)isthesoundpressurelevelofthemaskingcomponentwiththeindexnumberjatthecorrespondingcriticalbandratez(j).ThetermaviscalledthemaskingindexandvfthemaskingfunctionofthemaskingcomponentXtmz(j).Themaskingindexavisdifferentfortonalandnon-tonalmasker(avtmandavnm).F

29、ortonalmaskersitisgivenbyavtm=-1.525-0.275*z(j)-4.5dB,andfornon-tonalmaskersavnm=-1.525-0.175*z(j)-0.5dB.Themaskingfunctionvfofamaskerischaracterizedbydifferentlowerandupperslopes,whichdependonthedistanceinBarkdz=z(i)-z(j)tothemasker.Inthisexpressioniistheindexofthespectrallineatwhichthemaskingfunct

30、ioniscalculatedandjthatofthemasker.Thecriticalbandratesz(j)andz(i)canbefoundinTables3-D.1a,3-D.1b,3-D.1cforLayerI;Tables3-D.1d,3-D.1e,3-D.1fforLayerII,Frequencies,CriticalBandRatesandAbsoluteThreshold.Themaskingfunction,whichisthesamefortonalandnon-tonalmaskers,isgivenby:vf=17*(dz+1)-(0.4*Xz(j)+6)dB

31、for-3=dz-1Barkvf=(0.4*Xz(j)+6)*dzdBfor-1=dz0Barkvf=-17*dzdBfor0=dz1Barkvf=-(dz-1)*(17-0.15*Xz(j)-17dBfor1=dz8BarkIntheseexpressionsXz(j)isthesoundpressurelevelofthejthmaskingcomponentindB.Ifdz=8Bark,themaskingisnolongerconsidered(LTtmandLTnmaresetto-8dBoutsidethisrange).Step7:Calculationoftheglobalm

32、askingthresholdLTgTheglobalmaskingthresholdLTg(i)attheithfrequencysampleisderivedfromtheupperandlowerslopesoftheindividualmaskingthresholdofeachofthejtonalandnon-tonalmaskers,andinadditionfromthethresholdinquietLTq(i).ThisisalsogiveninTables3-D.1a,3-D.1b,3-D.1cforLayerI;Tables3-D.1d,3-D.1e,3-D.1ffor

33、LayerIIFrequencies,CriticalBandRatesandAbsoluteThreshold.Theglobalmaskingthresholdisfoundbysummingthepowerscorrespondingtotheindividualmaskingthresholdsandthethresholdinquiet.LTg(i)=10log(10LTq(i)/10+)Thetotalnumberoftonalmaskersisgivenbym,andthetotalnumberofnon-tonalmaskersisgivenbyn.Foragiveni,the

34、rangeofjcanbereducedtojustencompassthosemaskingcomponentsthatarewithin-8to+3Barkfromi.OutsideofthisrangeLTtmandLTnmare-8dB.Step8:DeterminationoftheminimummaskingthresholdTheminimummaskinglevelLTmin(n)insubbandnisdeterminedbythefollowingexpression:LTmin(n)=MINLTg(i)dBf(i)insubbandnwheref(i)isthefrequ

35、encyoftheithfrequencysample.Thef(i)aretabulatedintheTables3-D.1a,3-D.1b,3-D.1cforLayerI;Tables3-D.1d,3-D.1e,3-D.1fforLayerIIofFrequencies,CriticalBandRatesandAbsoluteThreshold.AminimummaskinglevelLTmin(n)iscomputedforeverysubband.Step9:Calculationofthesignal-to-mask-ratioThesignal-to-maskratioSMRsb(

36、n)=Lsb(n)-LTmin(n)dBiscomputedforeverysubbandn.Table3-D.1a.:Frequencies,CriticalBandRatesandAbsoluteThresholdTableisvalidforLayerIatasamplingrateof32.0kHz.IndexNumberFrequencyCrit.BandRateAbsoluteThresh.iHzzdB162.50.61733.442125.001.23219.203187.501.84213.874250.002.44511.015312.503.0379.206375.003.

37、6187.947437.504.1857.008500.004.7366.289562.505.2725.7010625.005.7895.2111687.506.2894.8012750.006.7704.4513812.507.2334.1414875.007.6773.8615937.508.1033.61161000.008.5113.37171062.508.9013.15181125.009.2752.93191187.509.6322.73201250.009.9742.53211312.5010.3012.32221375.0010.6142.12231437.5010.913

38、1.92241500.0011.1991.71251562.5011.4741.49261625.0011.7361.27271687.5011.9881.04281750.0012.230.80291812.5012.461.55301875.0012.684.29311937.5012.898.02322000.0013.104-.25332062.5013.302-.54342125.0013.493-.83352187.5013.678-1.12362250.0013.855-1.43372312.5014.027-1.73382375.0014.193-2.04392437.5014

39、.354-2.34402500.0014.509-2.64412562.5014.660-2.93422625.0014.807-3.22432687.5014.949-3.49442750.0015.087-3.74452812.5015.221-3.98462875.0015.351-4.20472937.5015.478-4.40483000.0015.602-4.57493125.0015.841-4.82503250.0016.069-4.96513375.0016.287-4.97523500.0016.496-4.86533625.0016.697-4.63543750.0016

40、.891-4.29553875.0017.078-3.87564000.0017.259-3.39574125.0017.434-2.86584250.0017.605-2.31594375.0017.770-1.77604500.0017.932-1.24614625.0018.089-.74624750.0018.242-.29634875.0018.392.12645000.0018.539.48655125.0018.682.79665250.0018.8231.06675375.0018.9601.29685500.0019.0951.49695625.0019.2261.66705

41、750.0019.3561.81715875.0019.4821.95726000.0019.6062.08736250.0019.8472.33746500.0020.0792.59756750.0020.3002.86767000.0020.5133.17777250.0020.7173.51787500.0020.9123.89797750.0021.0984.31808000.0021.2754.79818250.0021.4455.31828500.0021.6065.88838750.0021.7606.50849000.0021.9067.19859250.0022.0467.9

42、3869500.0022.1788.75879750.0022.3049.638810000.0022.42410.588910250.0022.53811.609010500.0022.64612.719110750.0022.74913.909211000.0022.84715.189311250.0022.94116.549411500.0023.03018.019511750.0023.11419.579612000.0023.19521.239712250.0023.27223.019812500.0023.34524.909912750.0023.41526.9010013000.

43、0023.48229.0310113250.0023.54631.2810213500.0023.60733.6710313750.0023.66636.1910414000.0023.72238.8610514250.0023.77541.6710614500.0023.82744.6310714750.0023.87647.7610815000.0023.92351.04Table3-D.1b.:Frequencies,CriticalBandRatesandAbsoluteThresholdTableisvalidforLayerIatasamplingrateof44.1kHz.Ind

44、exNumberFrequencyCrit.BandRateAbsoluteThresh.iHzzdB186.13.85025.872172.271.69414.853258.402.52510.724344.533.3378.505430.664.1247.106516.804.8826.117602.935.6085.378689.066.3014.799775.206.9594.3210861.337.5813.9211947.468.1693.57121033.598.7233.25131119.739.2442.95141205.869.7342.67151291.9910.1952

45、.39161378.1310.6292.11171464.2611.0371.83181550.3911.4211.53191636.5211.7831.23201722.6612.125.90211808.7912.448.56221894.9212.753.21231981.0513.042-.17242067.1913.317-.56252153.3213.578-.96262239.4513.826-1.38272325.5914.062-1.79282411.7214.288-2.21292497.8514.504-2.63302583.9814.711-3.03312670.121

46、4.909-3.41322756.2515.100-3.77332842.3815.284-4.09342928.5215.460-4.37353014.6515.631-4.60363100.7815.796-4.78373186.9115.955-4.91383273.0516.110-4.97393359.1816.260-4.98403445.3116.406-4.92413531.4516.547-4.81423617.5816.685-4.65433703.7116.820-4.43443789.8416.951-4.17453875.9817.079-3.87463962.111

47、7.205-3.54474048.2417.327-3.19484134.3817.447-2.82494306.6417.680-2.06504478.9117.905-1.32514651.1718.121-.64524823.4418.331-.04534995.7018.534.47545167.9718.731.89555340.2318.9221.23565512.5019.1081.51575684.7719.2891.74585857.0319.4641.93596029.3019.6352.11606201.5619.8012.28616373.8319.9632.46626

48、546.0920.1202.63636718.3620.2732.82646890.6320.4213.03657062.8920.5653.25667235.1620.7053.49677407.4220.8403.74687579.6920.9724.02697751.9521.0994.32707924.2221.2224.64718096.4821.3424.98728268.7521.4575.35738613.2821.6776.15748957.8121.8827.07759302.3422.0748.10769646.8822.2539.25779991.4122.42010.

49、547810335.9422.57611.977910680.4722.72113.568011025.0022.85715.318111369.5322.98417.238211714.0623.10219.348312058.5923.21321.648412403.1323.31724.158512747.6623.41526.888613092.1923.50629.848713436.7223.59233.058813781.2523.67336.528914125.7823.74940.259014470.3123.82144.279114814.8423.88848.599215

50、159.3823.95253.229315503.9124.01358.189415848.4424.07063.499516192.9724.12568.009616537.5024.17668.009716882.0324.22568.009817226.5624.27168.009917571.0924.31668.0010017915.6324.35868.0010118260.1624.39868.0010218604.6924.43668.0010318949.2224.47368.0010419293.7524.50868.0010519638.2824.54268.001061

51、9982.8124.57468.00Table3-D.1c.Frequencies,CriticalBandRatesandAbsoluteThresholdTableisvalidforLayerIatasamplingrateof48kHz.IndexNumberFrequencyCrit.BandRateAbsoluteThresh.iHzzdB193.75.92524.172187.501.84213.873281.252.74210.014375.003.6187.945468.754.4636.626562.505.2725.707656.256.0415.008750.006.7

52、704.459843.757.4574.0010937.508.1033.61111031.258.7083.26121125.009.2752.93131218.759.8052.63141312.5010.3012.32151406.2510.7652.02161500.0011.1991.71171593.7511.6061.38181687.5011.9881.04191781.2512.347.67201875.0012.684.29211968.7513.002-.11222062.5013.302-.54232156.2513.586-.97242250.0013.855-1.4

53、3252343.7514.111-1.88262437.5014.354-2.34272531.2514.585-2.79282625.0014.807-3.22292718.7515.018-3.62302812.5015.221-3.98312906.2515.415-4.30323000.0015.602-4.57333093.7515.783-4.77343187.5015.956-4.91353281.2516.124-4.98363375.0016.287-4.97373468.7516.445-4.90383562.5016.598-4.76393656.2516.746-4.5

54、5403750.0016.891-4.29413843.7517.032-3.99423937.5017.169-3.64434031.2517.303-3.26444125.0017.434-2.86454218.7517.563-2.45464312.5017.688-2.04474406.2517.811-1.63484500.0017.932-1.24494687.5018.166-.51504875.0018.392.12515062.5018.611.64525250.0018.8231.06535437.5019.0281.39545625.0019.2261.66555812.

55、5019.4191.88566000.0019.6062.08576187.5019.7882.27586375.0019.9642.46596562.5020.1352.65606750.0020.3002.86616937.5020.4613.09627125.0020.6163.33637312.5020.7663.60647500.0020.9123.89657687.5021.0524.20667875.0021.1884.54678062.5021.3184.91688250.0021.4455.31698437.5021.5675.73708625.0021.6846.18718

56、812.5021.7976.67729000.0021.9067.19739375.0022.1138.33749750.0022.3049.637510125.0022.48211.087610500.0022.64612.717710875.0022.79914.537811250.0022.94116.547911625.0023.07218.778012000.0023.19521.238112375.0023.30923.948212750.0023.41526.908313125.0023.51530.148413500.0023.60733.678513875.0023.6943

57、7.518614250.0023.77541.678714625.0023.85246.178815000.0023.92351.048915375.0023.99156.299015750.0024.05461.949116125.0024.11468.009216500.0024.17168.009316875.0024.22468.009417250.0024.27568.009517625.0024.32268.009618000.0024.36868.009718375.0024.41168.009818750.0024.45268.009919125.0024.49168.0010

58、019500.0024.52868.0010119875.0024.56468.0010220250.0024.59768.00Table3-D.1d.:Frequencies,CriticalBandRatesandAbsoluteThresholdTableisvalidforLayerIIatasamplingrateof32.0kHz.IndexNumberFrequencyCrit.BandRateAbsoluteThresh.iHzzdB131.25.30958.23262.50.61733.44393.75.92524.174125.001.23219.205156.251.53

59、816.056187.501.84213.877218.752.14512.268250.002.44511.019281.252.74210.0110312.503.0379.2011343.753.3298.5212375.003.6187.9413406.253.9037.4414437.504.1857.0015468.754.4636.6216500.004.7366.2817531.255.0065.9718562.505.2725.7019593.755.5335.4420625.005.7895.2121656.256.0415.0022687.506.2894.8023718

60、.756.5324.6224750.006.7704.4525781.257.0044.2926812.507.2334.1427843.757.4574.0028875.007.6773.8629906.257.8923.7330937.508.1033.6131968.758.3093.49321000.008.5113.37331031.258.7083.26341062.508.9013.15351093.759.0903.04361125.009.2752.93371156.259.4562.83381187.509.6322.73391218.759.8052.63401250.0