Telos Zephyr Xstream - Manual (Page 182)

USER’S MANUAL
Section 10: APPLICATIONS GUIDE 170
10.2 Choosing the Best Transmit Mode for your application
FIDELITY versus CODING METHOD versus DELAY – A quick comparison
We have listed the different modes here in approximate order of delay. See Section 6 (Audio
Coding Reference) for more information on the Quality and Delay of the various coding
methods.
G.722
Offers 7kHz audio frequency response at moderate fidelity. It operates at 56‐64kbps per
channel. Sample rate is 16kHz. The frequency response is 7.5 kHz. G>722 was originally
designed for “enhanced” telephone applications. It is widely supported by other codecs. It’s
very low delay (less than 20 msec) makes this coding method very popular for cueing or foldback
(IFB) channels.
AAC-LD
AAC‐LD offers fidelity equivalent to Layer‐3 with very low delay (about 70 msec). It is an
excellent choice for situations where live interaction is required.
AAC‐LD offers 14 kHz audio frequency response.
AAC
AAC offers Layer‐2 quality at 50% of the bit rate. The fidelity of stereo at 128kbps meets the ITU
(International Telecommunications Union) criteria for "Indistinguishable Quality" for stereo
transmission. The delay is quite low, at less than 1/5th second.
AAC should be used whenever it is supported at both ends.
Offers 15 or 20 kHz audio frequency response, at 32 or 48 kHz sample rate, respectively
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COMPATIBILITY TIP!
Zephyr Xstream supports both 32kHz and 48kHz sample rate for Layer-2 in the following
modes. The majority of Layer-2 codecs deployed in the field (including the Zephyr Classic)
support the 48 kHz sample rate only.
The Layer 2 Mono/Half mode allows operation at 24 kHz sample rate, however the delay is
significantly increased.
Layer-2
L2 Mono 64 & L2 Stereo– Offers 7.8kHz (at 56kbps) or 9.8 kHz (at 64kbps) at moderate fidelity.
Sample rate is 32 or 48kHz. It is generally preferred over G.722 for music, but not always for
voice. Sibilance causes obvious artifacts. When the 48 kHz sample rate is used, the delay is
moderately low (1/4 second for stereo, 1/10 second for mono) however the increased