RoadRunner
U S E R S G U I D E
48
The only constraint on the far-end codecs is that thy must be configured
set to decoder independent YES.
Advanced Encoder and Decoder Settings
ACE:
E & D
ON or OFF
Sine Detector:
E
ON or OFF
ISO Header:
E
Individually selectable—Copyright,
Emphasis, Original, Protect and Private
Mute:
D
ON or OFF
Channel:
D
Left or Right
Status Bits:
D
Monitor state of user header bits
Error protection (ACE)
Transmission errors causing audio dropouts can ruin any session.
MUSICAM USA has incorporated several layers of error protection into
all of its MPEG codecs.
The first level of error protection, which has already been discussed, is
having the encoder slave to the incoming bit stream. This is the
‘decoder independent NO’ setting as discussed in the previous chapter.
The best example of what this does is if you are configured at 112 or 128
kb/s, MPEG Layer 2 using the 2-line mode. If one line is lost, you do
not lose audio. The decoder independent NO mode allows the encoder
to reconfigure to 64 kb/s as soon as the decoder senses that only 64
kb/s of information is present. There will be a reduction in fidelity, but
audio will not be lost. This mode works for all MPEG Layer 2
algorithms when connecting to any product manufactured by
MUSICAM USA or CCS Audio Products.
A second layer of error protection, Advanced Concealment of Errors
(ACE) uses the MPEG Layer 2 Scale Factor protection to mask any
transmission errors. ACE should be used when less than ideal ISDN
lines are used, or when occasional audio artifacts caused by line errors
cannot be tolerated. Scale factor protection is
not
supported by all
codecs. Only MUSICAM USA’s
CDQ
Prima
Series
Prima LT
Series and
RoadRunner
codecs support ACE. ACE is also
not
bi-directional. If
you enable scale factor protection on your encoder, the far end decoder
must also enable scale factor protection or audio is muted.
In order for ACE to work and for the codecs to pass audio, the near-end
encoder and the far-end decoder must both activate ACE. Encoder and