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Telos Zephyr Xstream Two-Way Radio User Manual

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USER’S MANUAL

Section 6: AUDIO CODING REFERENCE 127

AAC AAC-LD Layer-3 Layer-2 G.722

Delay :

Stereo (128kbps):

Sample Rate: --

32 kHz 242 msec 96 msec 452 msec 332 msec --

48 kHz 190 msec 68 msec 326 msec 220 msec --

Mono (64kbps):

Sample Rate:

16 kHz -- -- -- 590 14 msec

24kHz -- -- -- 402 msec --

32 kHz 284 msec 88 msec 390 msec 308 msec --

48 kHz 240 msec 56 msec 316 msec 208 msec --

Stereo (64kbps):

AAC @ 32kHz SR 404 msec -- -- -- --

Coding "Power"

16:1 - 18:1 12:1 12:1 6-8:1, 12:1 in

Joint stereo

4:1

Number of Bands

2048 2048 576 32 2

Notes:

* Layer-2 mono or discrete stereo @ 48 kHz sample rate yields 7.8 kHz audio response at 56 kbps and 9.8 kHz at 64 kbps

Delay will vary depending on ISDN network delay and other factors. Typical figures for encode-to-decode delay are given (network delay is not

included).

Frequency response is for swept sine test; response with program material will vary owing to the dynamic nature of the coding process.

Asyoucanseefromabove,theZephyrXstreamofferssuchawiderangeofoptionsforseveral

reasons:

• Tooptimizethetradeoffbetweendelayandquality(seebelow);

• Tooffercompatibilitywiththelargevarietyofequipmentdeployedin

existinginstallations.

• Toofferarangeofdelayvs.quali

tytoaccommodatedifferent

programmingscenarios.

Delay vs. Quality

Lookingatthechart,onethingthatshouldbeapparentisthattheregenerallyisatrade‐off

betweendelayandaudioperformance.Layer3’sexcellentaudioperformancerequiresa

significantdelay.Thisisbecausesomeofitspowercomesfromtheabilitytoana

lyzetheaudio

overarelativelylongperiod.LayerIIrequiresthenextlongestdelay,followedbyAAC,AAC‐LD

andG.722.AAC‐LDandG.722haveminimaldelay.

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