Dolby Laboratories DP570 D.5 Downmixing

90 Dolby® DP570 Multichannel Audio Tool User’s Manual
A Guide to Dolby Metadata
•Speech
MaxBoost:15dB(below–50dB)
BoostRange:–50to–31dB(5:1ratio)
NullBandWidth:5dB(–31to–26dB)
EarlyCutRange:–26to–16dB(2:1ratio)
CutRange:–16to+4dB(20:1ratio)
•None
NoDRCprofileselected.Thedialoguelevelparameterisstillapplied.
ThesechoicesareavailabletothecontentproducerforbothLinemodeandRFmode.The
contentproducerchooseswhichoftheseprofilestoassigntoeachmode;whenthe
consumerordecoderselectsaDRCmode,theprofilechosenbytheproducerisapplied.
InadditiontotheDRCprofile,metadatacanlimitsignalpeakstopreventclippingduring
downmixing.Thismetadata,knownasoverloadprotection,isinsertedbytheencoderonly
ifnecessary.Forexample,considera5.1‐channelprogramwithsignalsatdigitalfull‐scale
onallchannelsbeingplayedthroughastereo,downmixedline‐leveloutput.Withoutsome
formofattenuationorlimiting,theoutputsignalwouldobviouslyclip.Correctsettingof
theDialogueLevelandDRCprofilesnormallypreventsclippingandunnecessary
applicationofautomaticoverloadprotection.
D.5 Downmixing
DownmixingisafunctionofDolbyDigitalthatallowsamultichannelprogramtobe
reproducedoverfewerspeakerchannelsthanthenumberforwhichtheprogramis
optimallyintended.Simplyput,downmixingallowsconsumerstoenjoyaDVDordigital
televisionbroadcastwithoutrequiringafull‐blownhometheatersetup.
Aswithstereomixingwherethemixismonitoredinmonoonoccasiontomaintain
compatibility,multichannelaudiomixingrequirestheengineertoreferencethemixto
fewerspeakerchannelstoensurecompatibilityindownmixingsituations.Inthisway,
DolbyDigital,usingthemetadataparametersthatcontroldownmixing,isan“equal
opportunitytechnology,”inthateveryconsumerwhoreceivestheDolbyDigitaldata
streamcanenjoythebestaudioreproductionpossible,regardlessoftheplaybacksystem.
Itisimportanttoconsidertheoutputsignalsfromeachpieceofequipmentthatcanreceive
aDolbyDigitalprograminthehome.Table D ‐2showstheoutputtypesfromdifferent
equipment.
Note: DRCprofilesettingsaredependentonanaccuratedialoguelevelsetting.Improper
settingofthedialoguelevelparametermayresultinexcessiveandaudible
applicationofoverload‐protectionlimiting.
Table D-2 Outputs from Different Equipment Types
Equipment
Output
Digital 5.1-Channel
Analog 2-Channel Analog RF Remodulated
5.1‐channelamplifier
Thestandardhometheater
A/Vamp
××
5.1‐channeldecoder × ×