- Dolby Multichannel Audio Tool User's Manual

86 Dolby
®
DP570 Multichannel Audio Tool User’s Manual
A Guide to Dolby Metadata
Special Parameters
ThereareprofessionalparametersintheDolbyEbitstreamthatarenotunderdirectuser
control,suchasTimecodeandPitchShift.
Timecode
DolbyEbitstreamscarrytimecodeinformationinhours:minutes:seconds:framesformat.
Pitch Shift
ThePitchShiftparametercanbegeneratedautomaticallybyaDolbyEdecodertocontrol
theDolbyModel585TimeScalingProcessor.IftheinputtotheDolbyEdecoderisnotat
normalplayspeed(aswithvarispeedorprogramplay),thenthePitchShiftCode
parameterindicatestheamount
ofaudiopitchshiftingrequiredtorestoretheoriginal
programpitch.
D.2 Dialogue Level
DialogueLevelisperhapsthesinglemostimportantmetadataparameter.TheDialogue
LevelSetvaluerepresentsthelong‐termlevelofdialoguewithinapresentation,measured
accordingtoITU‐RRec.BS.1770.ThislevelcanbequantifiedwiththeDolbyLM100
BroadcastLoudnessMeter.
Whenreceivedattheconsumer’sDolbyDigital
decoder,thisparametersettingdetermines
alevelshi ftinthedecoderthatsets,ornormalizes,theaverageaudiooutputofthedecoder
toapresetlevel.Thisaidsinmatchingaudiovolumebetweenprogramsources.
Inbroadcasttransmission,thepropersettingofDialogueLevelensuresthattheconsumer
receivesastandard
listeninglevel,soswitchingchannelsorwatchingatelevisionprogram
throughthecommercialbreaksdoesn’trequireadjustingthevolume.Usingthesame
standardforallcontent,whetherconveyedbybroadcasttelevision,DVD,orothermedia,
enablestheconsumertoswitchbetweensourcesandprogramswhilemaintaininga
comfortableandconsistent
listeninglevel.
Thepropersetting oftheDialogueLevelparameteralsoenablestheDynamicRange
Controlprofileschosenbythecontentproducertoworkasintendedinless‐than‐optimal
listeningenvironments,andisessentialinanycontentproduction,whetheritisfor
transmissioninabroadcaststreamorfordirect
distributiontoconsumers,aswithDVDs.
The Scale
ThescaleusedintheDialogueLevelsettingrangesin1dBstepsfrom–1to–31dB.
Contrarytowhatyoumightassumeatfirst,asettingof–31representsnolevelshiftinthe
consumer’sdecoder,and–1representsthemaximumlevelshift.Here’swhy:
Note: Programswithoutdialogue,suchasanall‐musicprogram,stillrequireacareful
settingoftheDialogueLevelparameter.Whensetting theparameterforsuch
content,itisusefultocomparetheprogramtothelevelofotherprograms.Thegoal
istoallowtheconsumertoswitchtoyour
programwithouthavingtoadjustthe
volumecontrol.