- Dolby Multichannel Audio Tool User's Manual

88 Dolby
®
DP570 Multichannel Audio Tool User’s Manual
A Guide to Dolby Metadata
TheDolbyDigitalstreamcarriesmetadataforthetwopossibleoperatingmodesinthe
decoder.TheoperatingmodesareknownasLinemodeandRFmodeduetothetypeof
outputtheyaretypicallyassociatedwith.Linemodeistypicallyusedondecoderswithsix‐
ortwochannelline
leveloutputsandRFmodeisusedondecodersthathavean
RFremodulatedoutput.Fullfeatureddecodersallowtheconsumertoselectwhetherto
useDRCandifso,whichoperatingmodetouse.TheconsumerseesoptionssuchasOff,
LightCompression,andHeavyCompressioninsteadofNone,
Linemode,andRFmode.
AdvanceddecodersmayalsoallowcustomscalingoftheDRCmetadata.
Allthatneedstobedoneduringmetadataauthoring,orencoding,isselectionofthe
dynamicrangecontrolprofilesforLinemodeandRFmode.Theprofilesaredescribedin
thefollowingsections.
Line Mode
Linemodeoffersthesefeatures:
•Lowlevelsignalboostcompressionscalingisallowed.
•Highlevelsignalcutcompressionscalingisallowedwhennotdownmixing.
•Thenormalizeddialoguelevelisreproducedfromthedecoderataconstantloudness
levelof–31dBFSITURRec.BS.1770,assumingtheDialogueLevelparameterisset
correctly.
Linelevelorpowerampl ifiedoutputsfromtwochannelsettopdecoders,twochannel
digitaltelevisions,5.1channeldigitaltelevisions,DolbyDigitalA/Vsurrounddecoders,
andoutboardDolbyDigitaladaptersuseLinemode.
Consumercontrolofthedynamicrangeislimitedwhendownmixing.Productswithstereo
ormonooutputsdo
notusuallyallowconsumerscalingofLinemode.Thisisbecausethese
devicesareusuallydownmixing(forexample,whenreceivinga5.1channelsignal).
However,intheseproducts,theconsumermayhaveachoicebetweenLinemodeandRF
mode.
RF Mode
InRFmode,high‐andlowlevelcompressionscalingisnotallowed.WhenRFmodeis
active,thatcompressionprofileisalwaysfullyapplied.
RFmodeisdesignedforproducts(suchassettopboxes)thatgenerateadownmixedsignal
forconnectiontotheRF/antennainputofatelevisionset;however,
itisalsousefulin
situationswhereheavyDRCisrequired—forexample,whensmallPCspeakersareused
forDVDplayback.InRFmode,theoverallprogramlevelisraised11dB,thisresultsin
dialoguebeingreproducedatalevelof–20dBFS,whilethepeaksarelimitedto
prevent
signaloverloadintheD/Aconverter.Bylimitingheadroom,severeovermodulationof
televisionreceiversisprevented.The11dBgainprovidesanaverageloudnesslevelthat
compareswellwithexistinganalogtelevisionbroadcasts.
Note: WhiletheuseofDRCmodesduringdecodingisaconsumerselectablefeature,the
DialogueLevelparametersettingisnot.Therefore,settingtheDialogue Level
parameterproperlyisessentialbeforepreviewingaDRCprofile.