Telos Zephyr Xstream, User Manual

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USER’S MANUAL
Section 10: APPLICATIONS GUIDE 173
Voice-over applications communicating with non-Telos codecs
Most Common:
G.722 is the most commonly available coding mode in the world. Use G.722 for your Transmit &
Receive modes. Note: Since the quality of G.722 is only moderate, you should only use this
mode with clients who do not have a better option available. One B channel (1 call) required for
mono.
Most Popular:
MPEG Layer ‐ 2 Mono 128 seems to be the defacto standard used in the voice Industry. Set your
Transmit to L2 Mono 128 and your Receive to L2 . Two B channels (2 calls) required.
Use 48 kHz sample rate
Radio remotes (Mono) using a single B channel (1 call)
Good:
Field unit: L3 Dual/Mono Transmit and G.722 Receive
Studio unit: G.722 Transmit and L3 Dual/Mono Receive (Zephyr Xstream) or L3 Mono (Zephyr)
Use 32 kHz sample rate for best fidelity, or 48kHz sample rate for reduced delay
5
.
Better:
Field unit: AAC ‐ LD Mono 64 Transmit and G.722 Receive
Studio unit: G.722 Transmit and AAC ‐ LD Receive
This option has low round ‐ trip delay with fidelity comparable to Layer ‐ 3
5
.
Use 32 kHz sample rate for best fidelity or 48 kHz for reduced delay.
Best:
Field Unit: AAC Mono 64 Transmit and G.722 Receive.
Studio Unit: G.722 Transmit and AAC 64 Receive
This option has better fidelity than the AAC ‐ LD , but longer delay.
Use 32 kHz sample rate for best fidelity or 48 kHz for reduced delay
5
.
5
We know that this statement seems contradictory. The sample rate determines the "frame rate"
through the Xstream's DSP. Therefore, higher sample rates result in reduced delay.
However, the higher sample rate also increases the amount of raw data. This requires a higher
compression ratio to get the data to the target transmission rate. Therefore using the increased
sample rate may cause more audible artifacts, as compared to a lower rate.