Dolby Laboratories DP570 Line Mode, RF Mode

88 Dolby® DP570 Multichannel Audio Tool User’s Manual
A Guide to Dolby Metadata
TheDolbyDigitalstreamcarriesmetadataforthetwopossibleoperatingmodesinthe
decoder.TheoperatingmodesareknownasLinemodeandRFmodeduetothetypeof
outputtheyaretypicallyassociatedwith.Linemodeistypicallyusedondecoderswithsix‐
ortwo‐channelline‐leveloutputsandRFmodeisusedondecodersthathavean
RF‐remodulatedoutput.Full‐featureddecodersallowtheconsumertoselectwhetherto
useDRCandifso,whichoperatingmodetouse.TheconsumerseesoptionssuchasOff,
LightCompression,andHeavyCompressioninsteadofNone,Linemode,andRFmode.
AdvanceddecodersmayalsoallowcustomscalingoftheDRCmetadata.
Allthatneedstobedoneduringmetadataauthoring,orencoding,isselectionofthe
dynamicrangecontrolprofilesforLinemodeandRFmode.Theprofilesaredescribedin
thefollowingsections.
Line Mode
Linemodeoffersthesefeatures:
•Low‐levelsignalboostcompressionscalingisallowed.
•High‐levelsignalcutcompressionscalingisallowedwhennotdownmixing.
•Thenormalizeddialoguelevelisreproducedfromthedecoderataconstantloudness
levelof–31dBFSITU‐RRec.BS.1770,assumingtheDialogueLevelparameterisset
correctly.
Line‐levelorpower‐amplifiedoutputsfromtwo‐channelset‐topdecoders,two‐channel
digitaltelevisions,5.1‐channeldigitaltelevisions,DolbyDigitalA/Vsurrounddecoders,
andoutboardDolbyDigitaladaptersuseLinemode.
Consumercontrolofthedynamicrangeislimitedwhendownmixing.Productswithstereo
ormonooutputsdonotusuallyallowconsumerscalingofLinemode.Thisisbecausethese
devicesareusuallydownmixing(forexample,whenreceivinga5.1‐channelsignal).
However,intheseproducts,theconsumermayhaveachoicebetweenLinemodeandRF
mode.
RF Mode
InRFmode,high‐andlow‐levelcompressionscalingisnotallowed.WhenRFmodeis
active,thatcompressionprofileisalwaysfullyapplied.
RFmodeisdesignedforproducts(suchasset‐topboxes)thatgenerateadownmixedsignal
forconnectiontotheRF/antennainputofatelevisionset;however,itisalsousefulin
situationswhereheavyDRCisrequired—forexample,whensmallPCspeakersareused
forDVDplayback.InRFmode,theoverallprogramlevelisraised11dB,thisresultsin
dialoguebeingreproducedatalevelof–20dBFS,whilethepeaksarelimitedtoprevent
signaloverloadintheD/Aconverter.Bylimitingheadroom,severeovermodulationof
televisionreceiversisprevented.The11dBgainprovidesanaverageloudnesslevelthat
compareswellwithexistinganalogtelevisionbroadcasts.
Note: WhiletheuseofDRCmodesduringdecodingisaconsumer‐selectablefeature,the
DialogueLevelparametersettingisnot.Therefore,settingtheDialogueLevel
parameterproperlyisessentialbeforepreviewingaDRCprofile.