Dolby Laboratories DP570 D.3 Dynamic Range Control

88 Dolby® DP570 Multichannel Audio Tool User’s Manual

A Guide to Dolby Metadata Dynamic Range Control

D.3 Dynamic Range Control

Differenthomelisteningenvironmentspresentawiderangeofrequirementsfordynamic

range.Ratherthansimplycompressingtheaudioprogramatthetransmissionsourceto

workwellinthepoorestlisteningenvironments,DolbyDigitalencoderscalculateandsend

DynamicRangeControl(DRC)metadatawiththesignal.Thismetadatacanthenbe

appliedtothesignalbythedecodertoreducethesignal’sdynamicrange.

ThroughthepropersettingofDRCprofilesduringthemasteringprocess,thecontent

producercanprovidethebestpossiblepresentationofprogramcontentinvirtuallyany

listeningenvironment,regardlessofthequalityoftheequipment,numberofchannels,or

ambientnoiselevelintheconsumer’shome.

ManyDolbyDigitaldecodersoffertheconsumertheoptionofdefeatingtheDynamic

RangeControlmetadata,butsomedonot.Decoderswithsixdiscretechanneloutputs(full

5.1‐channelcapability)typicallyofferthisoption.Decoderswithstereo,mono,or

RF‐remodulatedoutputs,suchasthosefoundonDVDplayersandset‐topboxes,oftendo

not.Inthesecases,thedecoderautomaticallyappliesthemostappropriateDRCmetadata

forthedecoder’soperatingmode.

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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Leq(A),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

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.