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Telos Zephyr Xstream Two-Way Radio User Manual

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USER’S MANUAL

Section 6: AUDIO CODING REFERENCE 120

• Nodynamicblockswitchingisusedbecausetherequiredlook‐aheaddelay

istoobig.Thetemporalproblemthatcausespre‐echoesishandledbythe

TemporalNoiseShapingmodule.

• The“windowshape”ofthespectralfilterisenhancedtobeadaptive.

Normally,theshapeisasimplesinecur

ve,butAAC‐LDcanuseashapethat

hasaloweroverlapbetweenthebands.Thissignificantlyimproves

performancewithtransients,withoutaddinganydelay.



AmazingPerformance

Lowdelaywouldnotbeusefulifthequalitywasnotacceptable,ofcourse.SohowdoesAAC‐LD

stack‐up?Theresultsareshownbelow

:AAC‐LDisclearlybetterthanLayer‐3forhalfofthetest

items,andasgoodfortheremaininghalf.NotbadconsideringthatAAC‐LDhasafractionofthe

delay.

Performance comparison of Layer 3 and AAC-LD. A = AAC-LD, B = Layer 3.

ResultshereareverygoodforAAC‐LD.Testitemses01‐03arespeech.Sincemostmono

remotebroadcastsarespeech,youcanexpectaudioqualityevenbetterthanwiththefamiliar–

andalreadyperfectlyuseful–Layer‐3.Popmusicisthetestitemsc03andperformanceisgood

hereaswell

.Theoneslighttroublespotistheglockenspielatsm02…

Weexpectyouwillfindthismodeveryuseful.

ISO/MPEG LAYER-3

Afterextensivetestingbybroadcastingorganizationsaroundtheworldunderthedirectionof

theCCIR,ithadbeendesignatedasthemostpowerfulofthethreeaudiocodingsystems

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