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Telos Zephyr Xstream Two-Way Radio User Manual

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USER’S MANUAL

Section 10: APPLICATIONS GUIDE 171

compressionratiorequiredtoaccomplishthistaskpushestheLayer‐2codingtothelimit,with

obviousartifactspresent.

L2Mono‐128–Offers20kHzor15kHzfrequencyresponseatveryhighfidelity.Itoperatesat

112‐128kbps.Samplerateis48kHzor32kHz.ByusingbothISDNBchann

elsformono,youget

animprovedfidelitymono,howeverthiscausesthedelaytoincreasetoslightlyover1/4

second.Thelowcompressionratioalsomakesthismodeidealforscenarioswheretheaudiois

likelytogothroughadditionalcodedaudiolinkslaterinthetransmissionchain.Thismodeis

thedefactostandardforv

oice‐worktransmissions.

Thismodeshouldbeusedforcriticalmonomaterialwhenthefarendsitedoesnotsupport

MPEGAAC.

Layer-3 Modes

Layer‐3Dual/Mono(thisis2channelsofmono.Youcansendthemtoseparatesites,ifyou

wish)Thismodeoffers15kHz(usin

g32kHzsamplerate)or16kHz(using48kHzsamplerate)at

highfidelity.Fidelityisbetterusingthe32kHzsamplerateasthisreducesthecompression

ratio.Itoperatesat56–64kbpsperaudiochannel.Layer‐3codingallowshighfidelity

transmissionwhileusingonlyoneoftheISDNBchannels.DelayislongerthantheothersingleB

chann

elmethodsatover1/4second.IfyoucanonlyaffordtouseoneBchannel(orhavea

singleSwitched‐56line)thenthismodeoffersyoubetterfidelitythananyother,unlessthefar

endsupportsMPEGAAC(s

eeabove).

L3Mono128‐Offers22kHzmonowhenusingthe48kHzsamplerateand15kHzatthe32kHz

samplerate.Thismodeoffersareducedcompressionratio,andconsequentlybetterresilience

toartifactcausedbyfuturecodingcycles.Itoperatesat128or112kbpsdependingontheBi

t

RateselectedintheCODECmenu.

Z

Zephyr VS Zephyr Xstream !

Zephyr does not offer Layer 3 Mono 128 operation (although the Joint-stereo mode can be

used as a substitute for it).

However, the Zephyr can decode the Xstream's Layer 3 Mono-128 streams. Set the Zephyr to

L3 Stereo Rcv.

Layer‐3J‐stereo‐Offers15kHz(using32kHzsamplerate)or16kHz(using48kHzsamplerate)at

highfidelity.Fidelityisbetterwhenusingthe32kHzsamplerateasthisreducesthe

compressionratio.Itrequiresat112–128kbps.Becausethismodeexploitsthetypicalcenter

redundancypresentinmos

tstereomaterial,fidelityisimprovedascomparedtoLayer‐3Stereo

(at112–128kbps)orL3Mono(at56–64kbps).DelayislongerthanthesingleBchannel

methods,atnearly1/2second.ThismodeoffersthebestfidelityStereoavailableusingasingle

ISDNBRIcir

cuit,unlessthefarendsupportsMPEGAAC(seebelow).



Thatistheendofourquickoverview.Notethatahighersampleratedoesnotnecessarilyoffer

betterfidelity(duetotheincreasedcompressionratio)butitdoesdecreasedelay.

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