Telos Zephyr Xstream - Manual (Page 129)

USER’S MANUAL
Section 6: AUDIO CODING REFERENCE 117
The result of all this is that the researchers succeeded. AAC provides performance superior to
any known codec at bitrates greater than 64kbps, and excellent performance relative to the
alternatives at bitrates reaching as low as 16 kbps.
And the researchers succeeded in achieving the ITU goal. AAC is the first codec system to fulfill
the ITU requirements for indistinguishable quality at 128 kbps/stereo
2 . It has approximately
100% more coding power than Layer‐2 and 30% more power than the former MPEG
performance leader, Layer‐3. For more information on AAC, and the tests of it, see our web site
for a paper on the subject: www.telos‐systems.com.
Zephyr Xstream is the first broadcast codec to incorporate the power of AAC coding, resulting in
superior high‐fidelity audio at lower bitrates and with less delay than Layer‐3 or Layer‐2.
It is the most powerful coding method available in Zephyr Xstream, and we particularly like it
because it is perfectly matched to the bitrates available on ISDN BRI lines.
It offers:
• 20 kHz mono or stereo audio bandwidth.
• Significantly less delay than Layers 2 or 3.
• Full‐fidelity mono on a single 56/64kbps channel.
• CD quality stereo 3 on a single ISDN Telco circuit.
• Affordable, transparent, audio transmission for AM/FM radio or
television audio.
c
COMPTIBILITY TIP!
The Zephyr Xstream cannot receive two J-stereo 64 feeds from the far end (after
all, where would the audio be output?).
When connected to two different sites simultaneously you can receive an audio
feed back from each using G.722 or L3 Dual/Mono.
2 Subjective Evaluation of State-of-the-Art Two-Channel Audio Codecs, G. A. Soulodre,
T. Grusec, et al. Journal of the Audio Engineering Society; Vol. 46, #3; March 1998, Pg
164 - 177.
3 20kHz bandwidth, >96dB dynamic range... just like a CD. The encoding process can
cause some loss that a trained listener, using carefully-selected program material and
good monitors, could detect. However, most people won’t hear the loss, and there’s no
accepted way to measure it.