Telos Zephyr Xstream User Manual page 139

Delay :
Stereo (128kbps):
Sample Rate:
32 kHz 242 msec
48 kHz 190 msec
Mono (64kbps):
Sample Rate:
16 kHz --
24kHz --
32 kHz 284 msec
48 kHz 240 msec
Stereo (64kbps):
AAC @ 32kHz SR 404 msec
16:1 - 18:1
Coding "Power"
2048
Number of Bands
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:
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 analyze 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.
USER'S MANUAL
AAC AAC-LD
96 msec
68 msec
--
--
88 msec
56 msec
--
12:1
2048
•
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. quality to accommodate different
programming scenarios.
Layer-3
452 msec
326 msec
--
--
390 msec
316 msec
--
12:1
576
Section 6: AUDIO CODING REFERENCE 127
Layer-2 G.722
--
332 msec --
220 msec --
590 14 msec
402 msec --
308 msec --
208 msec --
-- --
6-8:1, 12:1 in 4:1
Joint stereo
32 2