USER’S MANUAL
Section 6: AUDIO CODING REFERENCE 124
h
HOT TIP!
Another characteristic of G.722’s statistical framing is that the decoder may remain locked
despite serious corruption of the data, although audio fidelity will degrade. In cases where
you are unable to get a good connection you may find this characteristic desirable, however
you will find that the fidelity will be substantially less under these circumstances.
CASCADING
This
section
is
preliminary,
as
coder
cascading
is
an
active
field
of
investigation
among
algorithm
designers,
standards
organizations,
and
users.
Telos
urges
you
to
be
wary
and
to
let
your
own
ears
be
the
final
judge
until
better
information
becomes
available.
Some
of
what
we
do
know:
•
Some
CCIR
tests
have
demonstrated
that
one
pass
of
Layer
‐
3
at
56/64kbps
can
be
cascaded
with
2
‐
5
passes
of
Layer
‐
2
operating
at
high
(/channel
mono;
Joint
Stereo)
bitrates
with
good
results.
•
Informal
tests
at
the
Telos
lab
with
two
passes
of
Zephyr
Layer
‐
3
have
proven
successful,
with
listeners
noticing
no
audible
degradation,
even
on
“difficult”
CDs.
•
Tests
with
APT
‐
X
followed
by
one
or
two
passes
of
Layer
‐
3
followed
by
APT
‐
X
proved
to
be
quite
acceptable.
•
One
user
has
reported
that
two
passes
of
Zephyr
Layer
‐
3,
followed
by
one
pass
of
SEDAT,
is
OK.
(Stereo
program
mode.)
•
The
goal
is
to
get
as
much
“coding
headroom”
as
possible
at
each
stage.
This
is
achieved
when
you:
a)
Use
the
most
possible
bits
at
each
stage,
with
the
least
possible
compression
(for
example,
by
lowering
the
sample
rate,
and
using
64kbps
rather
than
56kbps
connection).
This
why
we
offer
the
mono
128
modes.
and/or
b)
Use
the
more
powerful
coding
method
of
those
available
at
each
stage
Xstream
offers
you
the
AAC
for
this
reason.
c)
Reduce
the
number
of
coded
stages
in
the
chain.
At
the
moment,
we
offer
the
following
advice:
•
Use
coders
only
where
necessary.
Consider
the
alternatives
at
each
stage.
With
the
cost
of
hard
disk
capacity
falling,
is
it
really
necessary
to
crunch
at
that
point?
Summary of Contents for Zephyr Xstream
Page 2: ......
Page 26: ...USER S MANUAL Section 1 QUICK RESULTS 14...
Page 30: ...USER S MANUAL Section 2 INTRODUCTION Getting to Know the Zephyr Xstream 18...
Page 70: ...USER S MANUAL Section 3 GUIDED TOUR of the HARDWARE 58...
Page 144: ...USER S MANUAL Section 6 AUDIO CODING REFERENCE 132...
Page 164: ...USER S MANUAL Section 8 LIVEWIRETM IP Audio 152...
Page 310: ...USER S MANUAL Appendix 1 Codec Interoperability Information 298...
Page 320: ...USER S MANUAL Appendix 3 ISDN Cause Phrases Values 308...
Page 324: ...USER S MANUAL Appendix 4 Known Working SPID Formats by Telco 312...
Page 356: ...USER S MANUAL Appendix 9 Modular Cable Guide 344...
