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Analog Audio Distribution Amplifier User Guide
TM
BrightEye 33
Chroma
Thecolororchromacontentofasignal,consistingofthehueandsaturationoftheimage.Seealso
ColorDierence.
Component
Inacomponentvideosystem,thetotalityoftheimageiscarriedbythreeseparatebutrelated
components.Thismethodprovidesthebestimagedelitywiththefewestartifacts,butitrequires
threeindependenttransmissionpaths(cables).Thecommonlyusedcomponentformatsare
LuminanceandColorDierence(Y/Pr/Pb),andRGB.Itwasfartoounwieldyintheearlydaysofcolor
television to even consider component transmission.
Composite
Compositetelevisiondatesbacktotheearlydaysofcolortransmission.Thisschemeencodesthe
colordierenceinformationontoacolorsubcarrier.Theinstantaneousphaseofthesubcarrieristhe
color’s hue, and the amplitude is the color’s saturation or intensity. This subcarrier is then added onto
theexistingluminancevideosignal.Thistrickworksbecausethesubcarrierissetatahighenough
frequencytoleavespectrumfortheluminanceinformation.Butitisnotaseamlessmattertopull
the signal apart again at the destination in order to display it or process it. The resultant artifacts of
dotcrawl(alsoreferredtoaschromacrawl)areonlythemostobviousresult.Compositetelevisionis
themostcommonlyusedformatthroughouttheworld,eitherasPALorNTSC.Itisalsoreferredtoas
Encoded video.
Color Difference
ColorDierencesystemstakeadvantageofthedetailsofhumanvision.Wehavemoreacuityinour
blackandwhitevisionthanwedoincolor.Thismeansthatweneedonlytheluminanceinformationto
becarriedatfullbandwidth,wecanscrimponthecolorchannels.Inordertodothis,RGBinformation
isconvertedtocarryalloftheluminance(Yistheblackandwhiteofthescene)inasinglechannel.
Theothertwochannelsareusedtocarrythe“colordierence”.NotedasB-YandR-Y,thesetwosignals
describehowaparticularpixel“diers”frombeingpurelyblackandwhite.Thesechannelstypically
have only half the bandwidth of the luminance.
Decibel (dB)
The decibel is a unit of measure used to express the ratio in the amplitude or power of two signals. A
dierenceof20dBcorrespondstoa10:1ratiobetweentwosignals,6dBisapproximatelya2:1ration.
Decibels add while the ratios multiply, so 26 dB is a 20:1 ratio, and 14 dB is a 5:1 ratio. There are several
special cases of the dB scale, where the reference is implied. Thus, dBm refers to power relative to 1
milliwatt,anddBureferstovoltagerelativeto.775VRMS.TheoriginalunitofmeasurewastheBel(10
timesbigger),namedafterAlexanderGrahamBell.
dBFS
InDigitalAudiosystems,thelargestnumericalvaluethatcanberepresentedisreferredtoasFull
Scale.NovaluesoraudiolevelsgreaterthanFScanbereproducedbecausetheywouldbeclipped.
Thenominaloperatingpoint(roughlycorrespondingto0VU)mustbesetbelowFSinordertohave
headroomforaudiopeaks.ThisoperatingpointisdescribedrelativetoFS,soadigitalreferencelevel
of-20dBFShas20dBofheadroombeforehittingtheFSclippingpoint.