System User Guide / Owners Manual

tolockandhasa0.1Hzbandwidth.TypicalAES/EBUreceiverchipslockwithinafew

samplesandhaveabandwidthofaround10kHz.

Ifthelocalclockisveryclean,anarrowbandPLListhebestchoicebecauseallbut

thelowest-frequencyjitterintheexternalsyncisrejected.Aconverterdesigned

alongthoselineswillsoundstellarunderallconditions.Iftheexternalsyncisvery

clean,awidebandPLListhebestchoicebecausethelocaloscillator’sownerrors

willbecorrected.ThisisthecasewhereagoodexternalsyncliketheCC1improves

abudgetconverter,orevenapriceyone,beyondexpectations.

Ifthedesignerguesseswronghowever,atoo-fastPLLmightendupforcingan

otherwisefinelocaloscillatortoreproducefaithfullyeverybumpandhiccupinthe

externalsyncsignal.Equipmentconstructedalongtheselinessoundgoodinmas-

termodebutwillonlyimproveinslavemodeiftheexternalsyncisstablerthanthe

internaloscillator.Anunstableexternalsyncactuallymakesitsoundworse.

Alternativelyatoo-slowPLLmightnotcorrectalocaloscillatorofsuboptimalqual-

ity.Inthatcase,jitterperformanceisbadregardlessofthequalityoftheexternal

clock.Andhereliestherub:aslowPLLwillalwaysmakeaconvertersoundthe

same,butnotnecessarilygood.Ifaconverterisinsensitivetoexternaljitter,that

aloneisnoindicationthatitsinternaljitterislow.AslowPLLshutsthedoorto

externaljitter,butalsotoanyimprovementtobehadfromexternalclockingwitha

verystablesource.

Inshort,onecannotexpectanexternalclocktoworkmiracleseverytime.IfthePLL

ofthereceivingdeviceisslow,thesoundqualitywillbeindependentofthequality

oftheexternalclock,forbetterorforworse.IfthePLLisfast,realimprovements

canbehad.

Byexample,thegraphbelowshowstheresultofmeasurementsonawellknown

DAWconverter.Thejitterperformance,measuredattheconverterchips’clockpin,

improvessubstantiallyatjitterfrequenciesbelow200HzwhenslavedtoaCC1.

100p

30p

10f

100f

10p

Jitte

(s)

Jitter density (s/sqrtHz)

20 20k50 100 200 500 1k 2k 5k 10k

DAW slaved to CC1

DAW (master)

CC1

JitterperformanceofawellknownDAWconverter